Search

Submerged macrophytes are crucial for the restoration of shallow eutrophic lake but they are diminished in coverage or lost with eutrophication. Their recovery after nutrient loading reduction depends on water and sediment nutrient levels. We studied the combined impacts of sediment fertility (low/high nitrogen and phosphorus content) and water nutrient concentrations (low/high nitrogen and phosphorus addition) on Vallisneria denseserrulata in a mesocosm experiment. We hypothesized that both the elevated external nutrient addition and high sediment nutrient contents would inhibit plant growth. We found that an increase in nutrient concentrations resulted in a significant increase in algal biomass. Furthermore, high external nutrient addition significantly reduced both the relative growth rate (RGR) and the density of V. denseserrulata growing in the nutrient-rich sediment, while in the nutrient-poor sediment treatment, RGR was not affected but the plant density decreased. Interestingly, low nutrient addition appeared to be more conducive to growth and reproduction of V. denseserrulata in the nutrient-rich sediment than in the nutrient-poor sediment. Our findings emphasize the importance of reducing external nutrient inputs is of key higher importance when restoring shallow eutrophic lakes, while the plants may benefit of the nutrient-rich sediment occurring in such lakes after eutrophication. [ABSTRACT FROM AUTHOR]

Coastal areas are at the centre of human–nature relationship, shaped by recreation, tourism and aesthetic values. However, socioeconomic drivers of biodiversity change in coastal areas have received less attention.Soft sediment seafloors support diverse species communities and contribute to ecosystem functionality. One of the main threats is dredging, which sweeps resident organisms. Dredgings are commonly done to deepen waterways, but also for the purposes of private housing. The ecological impacts of these small‐sized dredgings are not well known over broad environmental and geographical gradients.We developed a simple approach for spatial integration of ecological and socioeconomic system, to describe how recreational land use change contributes to the loss of marine biodiversity. It shows how human behaviour, such as preference for a location of second home, can be derived from spatial data and coupled with ecological change.We characterize typical locations of second homes based on accessibility, aesthetics and environment, and with the information identified suitable areas for new second homes. We also quantified typical areas of dredging, based on the depth and substrate of the sea floor, and the extent of the reed beds, influencing the access to properties. We then simulate an annual increase of new second homes and expected land‐use change, namely dredging of shores. Finally, we quantified the realized and projected loss of marine biodiversity from dredged sites, based on species distribution models, relying on extensive ecological data collected from over 170,000 underwater sites.We found that small‐sized dredging can be detrimental to coastal biodiversity, as dredging targets shallow, photic bays and lagoons, with diverse algal and aquatic plant communities, with limited recovery potential. Dredgings also had broad impacts on benthic faunal habitats, which maintain ecosystem processes and functions. Our results reveal a significant ecological change driven by recreational land use.Reversing the trend of biodiversity loss requires a holistic understanding of socioecological systems. Our results highlight the need for integrating land–sea interactions into conservation policies and reforming current land‐use regulation for the benefit of marine biodiversity. Read the free Plain Language Summary for this article on the Journal blog. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Societal Impact Statement Summary Seagrass meadows are a globally important habitat subject to significant loss. As efforts to restore these sensitive habitats are hampered by their high cost and low levels of reliability, rigorous guidance is required to improve effectiveness and ensure they are cost‐effective. Here, we define 10 golden rules for how we can undertake seagrass restoration. We do this by considering that for seagrass restoration to be successful, it needs to take place with people and not against people. The framework we present aims to direct efforts for seagrass restoration that are holistic and achieve broad goals for people, biodiversity and the planet.The world has lost a significant proportion of its seagrass, and although glimmers of hope for its recovery exist, losses and degradations continue. First and foremost, evidence highlights the need to put the world on a global pathway to seagrass net gain. Achieving this outcome requires that conservation of what remains is a priority, but reaching net gain requires seagrass coverage to increase at rates unlikely to be achieved naturally; large‐scale active restoration is required to fill this gap. Novel finance mechanisms aligned to the climate emergency and biodiversity crises are increasingly leading to larger scale restoration projects. However, no clear framework exists for developing or prioritising approaches. With seagrass restoration expensive and unreliable, rigorous guidance is required to improve effectiveness and ensure it is cost‐effective. Building on evidence from terrestrial and marine sources, here, we apply the ‘10 golden rules’ concept, first outlined for reforestation and later applied to coral reefs, to seagrass restoration. In doing so, we follow international standards for ecological restoration and view seagrass restoration in a broad context, whereby regeneration can be achieved either by planting or by enhancing and facilitating natural recovery. These rules somewhat differ from those on reforestation and coral reef restoration, principally due to the relative immaturity of seagrass restoration science. These 10 golden rules for seagrass restoration are placed within a coupled social‐ecological systems context, and we present a framework for conservation more broadly, to achieve multiple goals pertaining to people, biodiversity and the planet. [ABSTRACT FROM AUTHOR]

Urban rivers face sustained anthropogenic pressures limiting biodiversity. Yet, urban waterways such as the Detroit River are important habitat in supporting regional diversity. The Detroit River is a Great Lakes Area of Concern where conservation and restoration efforts prioritize improved biological and habitat integrity in the connecting channel. This study explores benthic macroinvertebrate in submerged aquatic vegetation across five mainstem channel wetlands and two tributary sites of the Canadian wetlands to describe spatial patterns and diversity. We first examine inter-wetland differences between five mainstem wetlands by hierarchical cluster analysis, NMDS and PERMANOVA, identifying two mainstem groups: one comprising of two middle reach wetlands (Detroit River Marshes and Grass Island), the second showed similarities among wetlands across all reaches (Turkey Creek, River Canard and Peche Island). The latter groupings shared similar habitat characteristics, deeper and finer grain-sizes, and functional feeding group characteristics - low abundances of shredders. Second objective, we perform an intra-wetland comparison for Turkey Creek and River Canard to analyze for differences along tributaries. At neither River Canard nor Turkey Creek we observed significant tributary influence on mainstem communities but had found the Turkey Creek tributary communities significantly differed from the channel communities. Diversity metrics and Hilsenhoff Biotic Index illustrate strained benthic communities across the river. We had also found water quality to be consistently moderately degraded. Our findings differ from prior analyses within emergent vegetation that indicate variable water quality conditions between mainstem and tributary and non-impaired macroinvertebrate communities. [ABSTRACT FROM AUTHOR]

Upper layer thickness (mixing depth) is an essential parameter for estimating the dissolved inorganic carbon and carbon flux at the water surface based on their association with the vertical flux of dissolved inorganic carbon. Previous studies quantified the mixing depth without SAV meadow or penetration depth in the SAV meadow without stratification and wind stress. However, mixing depth related to interaction with submerged aquatic vegetations (SAVs), stratification, and wind stress has yet to be quantified in the previous studies. Our study is the first to quantify the theoretical mixing depth with SAVs according to wind stress, SAV height, and drag coefficient. Theoretical mixing depth was quantified from modeled vertical temperature profile, vertical profile of horizontal velocity, and gradient Richardson number (Rig,veg). We found that mixing depth at a Rig,veg of 100 demonstrated good agreement with numerical results on average, with the mixing depth estimated in this study (hU,this study) showing high applicability to observations at Komuke Lagoon. Moreover, hU,this study increased with the increasing wind stress and decreasing drag coefficient and SAV height. Further, we found that SAV meadows with stratification and wind stress could be divided into four hydrodynamic regimes: non‐vegetated layers, upper vegetated layers, thermoclines, and benthic boundary layers. Our findings help us estimate mixing depth or vertical flux without complicated numerical simulation and understand flow interaction with SAV, wind stress, and stratification. Plain Language Summary: Upper layer thickness (mixing depth) and flow fields are important to estimate the carbon flux (e.g., "blue carbon") and the transportation of dissolved materials (e.g., dissolved oxygen, dissolved inorganic carbon, dissolved inorganic nitrogen, etc) in submerged aquatic vegetation (SAV) meadows. However, it may not be easy to estimate mixing depth without complex numerical simulations. Additionally, we have not understood the interaction of SAV meadows with stratification, currents, or waves. Our study is the first to quantify the mixing depth analytically and to show the hydrodynamic regimes in SAV meadows with stratification. Our finding helps us to estimate carbon flux and the transportation rate of dissolved materials easily without complicated numerical simulation. Key Points: Mixing depth with submerged aquatic vegetation (SAV) meadows was estimated using an average gradient Richardson number 100SAV meadows with stratification and wind stress were divided into four hydrodynamic regimesWind stress, SAV, and stratification effects were used to accurately estimate the mixing depth [ABSTRACT FROM AUTHOR]

Ecosystem state transitions can be ecologically devastating or be a restoration success. State transitions are common within aquatic systems worldwide, especially considering human‐mediated changes to land use and water use. We created a transferable conceptual framework to enable multiscale assessments of state resilience and early warnings of state transitions that can inform strategic restorations and avoid ecosystem collapse. The conceptual framework integrated machine learning predictions with ecosystem state concepts (e.g., state classification, gradients of vulnerability, and recovery potential leading to state transitions) and was devised to investigate possible environmental drivers. As an application of the framework, we generated prediction probabilities of submersed aquatic vegetation (SAV) presence at nearly 10,000 sites in the Upper Mississippi River (United States). Then, we used an interpretability method to explain model predictions to gain insights into possible environmental drivers and thresholds or linear responses of SAV presence and absence. Model accuracy was 89% without spatial bias. Average water depth, suspended solids, substrate, and distance to nearest SAV were the best predictors and likely environmental drivers of SAV habitat suitability. These environmental drivers exhibited nonlinear, threshold‐type responses for SAV. All the results are also presented in an online dashboard to explore results at many spatial scales. The habitat suitability model outputs and prediction explanations from many spatial scales (4 m to 400 km of river reach) can inform research and restoration planning. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation plays a fundamental role as a habitat for the biodiversity of marine species. To carry out the research and monitoring of submerged aquatic vegetation more efficiently and accurately, it is important to use advanced technologies such as underwater robots. However, when conducting underwater missions to capture photographs and videos near submerged aquatic vegetation meadows, algae can become entangled in the propellers and cause vehicle failure. In this context, a neurobiologically inspired control architecture is proposed for the control of unmanned underwater vehicles with redundant thrusters. The proposed control architecture learns to control the underwater robot in a non-stationary environment and combines the associative learning method and vector associative map learning to generate transformations between the spatial and velocity coordinates in the robot actuator. The experimental results obtained show that the proposed control architecture exhibits notable resilience capabilities while maintaining its operation in the face of thruster failures. In the discussion of the results obtained, the importance of the proposed control architecture is highlighted in the context of the monitoring and conservation of underwater vegetation meadows. Its resilience, robustness, and adaptability capabilities make it an effective tool to face challenges and meet mission objectives in such critical environments. [ABSTRACT FROM AUTHOR]

The organic carbon (Corg) stored in seagrass meadows is globally significant and could be relevant in strategies to mitigate increasing CO2 concentration in the atmosphere. Most of that stored Corg is in the soils that underlie the seagrasses. We explored how seagrass and soil characteristics vary among seagrass meadows across the geographic range of turtlegrass (Thalassia testudinum) with a goal of illuminating the processes controlling soil organic carbon (Corg) storage spanning 23° of latitude. Seagrass abundance (percent cover, biomass, and canopy height) varied by over an order of magnitude across sites, and we found high variability in soil characteristics, with Corg ranging from 0.08 to 12.59% dry weight. Seagrass abundance was a good predictor of the Corg stocks in surficial soils, and the relative importance of seagrass-derived soil Corg increased as abundance increased. These relationships suggest that first-order estimates of surficial soil Corg stocks can be made by measuring seagrass abundance and applying a linear transfer function. The relative availability of the nutrients N and P to support plant growth was also correlated with soil Corg stocks. Stocks were lower at N-limited sites than at P-limited ones, but the importance of seagrass-derived organic matter to soil Corg stocks was not a function of nutrient limitation status. This finding seemed at odds with our observation that labile standard substrates decomposed more slowly at N-limited than at P-limited sites, since even though decomposition rates were 55% lower at N-limited sites, less Corg was accumulating in the soils. The dependence of Corg stocks and decomposition rates on nutrient availability suggests that eutrophication is likely to exert a strong influence on carbon storage in seagrass meadows.

Substantial increases in non-native aquatic vegetation have occurred in the upper San Francisco Estuary over the last 2 decades, largely from the explosive growth of a few submerged and floating aquatic plant species. Some of these species act as ecosystem engineers by creating conditions that favor their further growth and expansion as well as by modifying habitat for other organisms. Over the last decade, numerous studies have investigated patterns of expansion and turn-over of aquatic vegetation species; effects of vegetation on ecosystem health, water quality, and habitat; and effects of particular species or communities on physical processes such as carbon and sediment dynamics. Taking a synthetic approach to evaluate what has been learned over the last few years has shed light on just how significant aquatic plant species and communities are to ecosystems in the Sacramento-San Joaquin Delta. Aquatic vegetation affects every aspect of the physical and biotic environment, acting as ecosystem engineers on the landscape. Furthermore, their effects are constantly changing across space and time, leaving many unanswered questions about the full effects of aquatic vegetation on Delta ecosystems and what future effects may result, as species shift in distribution and new species are introduced. Remaining knowledge gaps underlie our understanding of aquatic macrophyte effects on Delta ecosystems, including their roles and relationships with respect to nutrients and nutrient cycling, evapotranspiration and water budgets, carbon and sediment, and emerging effects on fish species and their habitats. This paper explores our current understanding of submerged and floating aquatic vegetation (SAV and FAV) ecology with respect to major aquatic plant communities, observed patterns of change, interactions between aquatic vegetation and the physical environment, and how these factors affect ecosystem services and disservices within the upper San Francisco Estuary.

Remote sensing is a valuable tool for surveying submerged aquatic vegetation (SAV) distribution patterns at extensive spatial and temporal scales. Only regular mapping over successive time periods (e.g., months, years) allows for a quantitative assessment of SAV loss or recolonization extent. Still, there are only a limited number of studies assessing temporal changes in SAV patterns. ESA Sentinel-2 (S2) has a high revisiting frequency permitting the multi-temporal assessment of SAV dynamics both seasonally and inter-annually. In the current study, a physics-based IDA (Image Data Analysis) model was used for the reconstruction of past SAV percent cover (%cover) patterns in the Baltic Sea coastal waters based on S2 archived images. First, we aimed at capturing and quantifying intra-annual spatiotemporal SAV dynamics happening during a growing season. Modeling results showed that significant changes took place in SAV %cover: the extent of low-cover (0–30% coverage) and intermediate-cover (30–70% coverage) areas decreased, while high-cover (70–100% coverage) areas increased during the growing period. Secondly, we also aimed at detecting SAV %cover spatiotemporal variations inter-annually (over the years 2016–2022). Inter-annual variability in %cover patterns was greater in the beginning of the vegetation period (May). The peak of the growing period (July/August) showed greater stability in the areal extent of the %cover classes. [ABSTRACT FROM AUTHOR]

Climate change and other anthropogenic factors have caused a significant decline in seagrass cover globally. Identifying the specific causes of this decline is paramount if they are to be addressed. Consequently, we identified the causes of long-term change in seagrass/submerged aquatic vegetation (SAV) percentage cover and extent in a marine protected area on Jamaica's southern coast. Two random forest regression (RFr) models were built using 2013 hydroacoustic survey SAV percentage cover data (dependent variable), and auxiliary and 2013 Landsat 7 and 8 reflectance data as the predictors. These were used to generate 24 SAV percentage cover and benthic feature maps (SAV present, absent, and coral reef) for the period 1984–2021 (37 years) from Landsat satellite series reflectance data. These maps and rainfall data were used to determine if SAV extent/area (km2) and average percentage cover and annual rainfall changed significantly over time and to evaluate the influence of rainfall. Additionally, rainfall impact on the overall spatial patterns of SAV loss, gain, and percentage cover change was assessed. Finally, the most important spatial pattern predictors of SAV loss, gain, and percentage cover change during 23 successive 1-to-4-year periods were identified. Predictors included rainfall proxies (distance and direction from river mouth), benthic topography, depth, and hurricane exposure (a measure of hurricane disturbance). SAV area/extent was largely stable, with >70% mean percentage cover for multiple years. However, Hurricane Ivan (in 2004) caused a significant decline in SAV area/extent (by 1.62 km2, or 13%) during 2002–2006, and a second hurricane (Dean) in 2007 delayed recovery until 2015. Additionally, rainfall declined significantly by >1000 mm since 1901, and mean monthly rainfall positively influenced SAV percentage cover change and had a positive overall effect on the spatial pattern of SAV cover percentage change (across the entire bay) and gain (close to the mouth of a river). The most important spatial pattern predictors were the two rainfall proxies (areas closer to the river mouth were more likely to experience SAV loss and gain) and depth, with shallow areas generally having a higher probability of SAV loss and gain. Three hurricanes had significant but different impacts depending on their distance from the southern coastline. Specifically, a hurricane that made landfall in 1988 (Gilbert), resulted in higher SAV percentage cover loss in 1987–1988. Benthic locations with a northwestern/northern facing aspect (the predominant direction of Ivan's leading edge wind bands) experienced higher SAV losses during 2002–2006. Additionally, exposure to Ivan explained percentage cover loss during 2006–2008 and average exposure to (the cumulative impact of) Ivan and Dean (both with tracks close to the southern coastline) explained SAV loss during 2013–2015. Therefore, despite historic lows in annual rainfall, overall, higher rainfall was beneficial, multiple hurricanes impacted the site, and despite two hurricanes in three years, SAV recovered within a decade. Hurricanes and a further reduction in rainfall may pose a serious threat to SAV persistence in the future. [ABSTRACT FROM AUTHOR]

Florida spring-fed rivers are known for their submerged aquatic vegetation (SAV). which provides habitat for fish and aquatic crustaceans and food for the Florida manatee. Salinization of coastal spring-fed rivers due to climate change and sea level rise have been documented and can cause changes 10 SAV communities. This study investigated patterns and relationships between the SAV community and salinity of the Chassahowitzka River (Citrus County, FL, USA) to extrapolate the long-term effects of river salinization. A distinct dichotomy was seen in the SAV community structure: communities where salt tolerant Chaetomorpha spp. was present and communities where freshwater filamentous algae species were present. Freshwater filamentous algae demonstrated an inverse relationship with salinity. Chaetomorpha spp. replaced the freshwater filamentous algae in regions too salty for freshwater algae to grow. These patterns in the SAV community resulted in three different ecological zones in the Chassahowitzka River: low salinity/freshwater tidal, transition, and brackish zones. While freshwater filamentous algae and Chaetomorpha spp. were characteristic of the freshwater and brackish zones respectively, both species were identified within the transition zone. Utilizing the presence/absence of these macroalgae types could allow for an in-situ approach of characterizing regions of coastal spring-fed rivers that show increased salinization. [ABSTRACT FROM AUTHOR]

Per- and polyfluoroalkyl substances (PFAS) are a class of manufactured chemicals that have been extensively utilized worldwide. We hypothesize that the presence, uptake, and accumulation of PFAS in aquatic vegetation (AV) is dependent upon several factors, such as the physiochemical properties of PFAS and proximity to potential sources. In this study, AV was collected from eight locations in Florida to investigate the PFAS presence, accumulation, and spatiotemporal distribution. PFAS were detected in AV at all sampling locations, with a range from 0.18 to 55 ng/g sum (∑)-PFAS. Individual PFAS and their concentrations varied by sampling location, time, and AV species. A total of 12 PFAS were identified, with the greatest concentrations measured in macroalgae. The average bioconcentration factor (BCF) among all samples was 1225, indicating high PFAS accumulation in AV from surface water. The highest concentrations, across all AV types, were recorded in the Indian River Lagoon (IRL), a location with a history of elevated PFAS burdens. The present study represents the first investigation of PFAS in naturally existing estuarine AV, filling an important gap on PFAS partitioning within the environment, as well as providing insights into exposure pathways for aquatic herbivores. Examining the presence, fate, and transport of these persistent chemicals in Florida's waterways is critical for understanding their effect on environmental, wildlife, and human health. [ABSTRACT FROM AUTHOR]

Copyright of Naturaliste Canadien is the property of La Societe Provancher and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Global-scale ocean acidification has spurred interest in the capacity of seagrass ecosystems to increase seawater pH within crucial shoreline habitats through photosynthetic activity. However, the dynamic variability of the coastal carbonate system has impeded generalization into whether seagrass aerobic metabolism ameliorates low pH on physiologically and ecologically relevant timescales. Here we present results of the most extensive study to date of pH modulation by seagrasses, spanning seven meadows (Zostera marina) and 1000 km of U.S. west coast over 6 years. Amelioration by seagrass ecosystems compared to non-vegetated areas occurred 65% of the time (mean increase 0.07 ± 0.008 SE). Events of continuous elevation in pH within seagrass ecosystems, indicating amelioration of low pH, were longer and of greater magnitude than opposing cases of reduced pH or exacerbation. Sustained elevations in pH of >0.1, comparable to a 30% decrease in [H+ ], were not restricted only to daylight hours but instead persisted for up to 21 days. Maximal pH elevations occurred in spring and summer during the seagrass growth season, with a tendency for stronger effects in higher latitude meadows. These results indicate that seagrass meadows can locally alleviate low pH conditions for extended periods of time with important implications for the conservation and management of coastal ecosystems.

Remote sensing is a valuable tool for surveying submerged aquatic vegetation (SAV) distribution patterns at extensive spatial and temporal scales. Only regular mapping over successive time periods (e.g., months, years) allows for a quantitative assessment of SAV loss or recolonization extent. Still, there are only a limited number of studies assessing temporal changes in SAV patterns. ESA Sentinel-2 (S2) has a high revisiting frequency permitting the multi-temporal assessment of SAV dynamics both seasonally and inter-annually. In the current study, a physics-based IDA (Image Data Analysis) model was used for the reconstruction of past SAV percent cover (%cover) patterns in the Baltic Sea coastal waters based on S2 archived images. First, we aimed at capturing and quantifying intra-annual spatiotemporal SAV dynamics happening during a growing season. Modeling results showed that significant changes took place in SAV %cover: the extent of low-cover (0–30% coverage) and intermediate-cover (30–70% coverage) areas decreased, while high-cover (70–100% coverage) areas increased during the growing period. Secondly, we also aimed at detecting SAV %cover spatiotemporal variations inter-annually (over the years 2016–2022). Inter-annual variability in %cover patterns was greater in the beginning of the vegetation period (May). The peak of the growing period (July/August) showed greater stability in the areal extent of the %cover classes.

Climate change and other anthropogenic factors have caused a significant decline in seagrass cover globally. Identifying the specific causes of this decline is paramount if they are to be addressed. Consequently, we identified the causes of long-term change in seagrass/submerged aquatic vegetation (SAV) percentage cover and extent in a marine protected area on Jamaica’s southern coast. Two random forest regression (RFr) models were built using 2013 hydroacoustic survey SAV percentage cover data (dependent variable), and auxiliary and 2013 Landsat 7 and 8 reflectance data as the predictors. These were used to generate 24 SAV percentage cover and benthic feature maps (SAV present, absent, and coral reef) for the period 1984–2021 (37 years) from Landsat satellite series reflectance data. These maps and rainfall data were used to determine if SAV extent/area (km2) and average percentage cover and annual rainfall changed significantly over time and to evaluate the influence of rainfall. Additionally, rainfall impact on the overall spatial patterns of SAV loss, gain, and percentage cover change was assessed. Finally, the most important spatial pattern predictors of SAV loss, gain, and percentage cover change during 23 successive 1-to-4-year periods were identified. Predictors included rainfall proxies (distance and direction from river mouth), benthic topography, depth, and hurricane exposure (a measure of hurricane disturbance). SAV area/extent was largely stable, with >70% mean percentage cover for multiple years. However, Hurricane Ivan (in 2004) caused a significant decline in SAV area/extent (by 1.62 km2, or 13%) during 2002–2006, and a second hurricane (Dean) in 2007 delayed recovery until 2015. Additionally, rainfall declined significantly by >1000 mm since 1901, and mean monthly rainfall positively influenced SAV percentage cover change and had a positive overall effect on the spatial pattern of SAV cover percentage change (across the entire bay) and gain (close to the mouth of a river). The most important spatial pattern predictors were the two rainfall proxies (areas closer to the river mouth were more likely to experience SAV loss and gain) and depth, with shallow areas generally having a higher probability of SAV loss and gain. Three hurricanes had significant but different impacts depending on their distance from the southern coastline. Specifically, a hurricane that made landfall in 1988 (Gilbert), resulted in higher SAV percentage cover loss in 1987–1988. Benthic locations with a northwestern/northern facing aspect (the predominant direction of Ivan’s leading edge wind bands) experienced higher SAV losses during 2002–2006. Additionally, exposure to Ivan explained percentage cover loss during 2006–2008 and average exposure to (the cumulative impact of) Ivan and Dean (both with tracks close to the southern coastline) explained SAV loss during 2013–2015. Therefore, despite historic lows in annual rainfall, overall, higher rainfall was beneficial, multiple hurricanes impacted the site, and despite two hurricanes in three years, SAV recovered within a decade. Hurricanes and a further reduction in rainfall may pose a serious threat to SAV persistence in the future.

Submerged aquatic vegetation (SAV) is a key functional group for the restoration of wetlands and aquatic ecosystems. It plays a vital role in the stability of ecosystem structure and function in shallow lakes and reservoirs. With Baiyangdian Lake as the research area, Landsat TM/ETM+/OLI and Sentinel-2 imagery datasets were used to explore the phenological characteristics of SAV over different time scales and construct a phenological map of the SAV groups. The long-term spatial distribution characteristics and trends of SAV from 1986 to 2021 were analyzed. The results show the following: (1) the harmonic analysis of time series (HANTS) eliminated abnormal observations and noise. Normalized difference vegetation index (NDVI) time series curves generated after HANTS accurately reflected the phenological characteristics of SAV. The early spring submerged aquatic vegetation (SAV1), such as Potamogeton crispus, entered the germination period in late February at the earliest (DOY = 53). The mature period ran from April to May, after which SAV1 began to decline gradually. The length of the growing season (LOS) was about 110 days. SAV2, which was represented by Ceratophyllum demersum, Myriophyllum verticillatum, and Potamogeton pectinatus, germinated in early April (DOY = 99). The mature period ran from July to September. The length of the growing season was 210 days. (2) The decision tree constructed based on the NDVI and modified normalized difference water index (MNDWI) identified SAV with an accuracy of 89.7%. (3) The distribution range of the SAV changed dramatically during 1986–2021. According to the area change, it can be divided into a shrinkage period, expansion period, degeneration period, and initial period of recovery. The succession trend of SAV provide a theoretical scientific basis and technical support for the ecological restoration and management of shallow lake ecosystems.

Submerged aquatic vegetation (SAV) are highly efficient at carbon sequestration and, despite their relatively small distribution globally, are recognized as a potentially valuable component of climate change mitigation. However, SAV mapping in tidal marshes presents a challenge due to optically complex constituents in the water. The emergence and advancement of deep learning-based techniques in the field of habitat mapping with remote sensing imagery provides an opportunity to address this challenge. In this study, an analytical framework was developed to quantify the carbon sequestration of SAV habitats in the Atchafalaya River Delta Estuary from field and remote sensing observations using deep convolutional neural network (DCNN) techniques. A U-Net-based model, Wetland-SAV Network, was trained to identify the SAV percent cover (high, medium, and low) as well as other estuarine habitat types from Landsat 8/9-OLI data. The areal extent of SAV was up to 8% of the total area (47,000 ha). The habitat areas and habitat-specific carbon fluxes were then used to quantify the net greenhouse gas (GHG) flux of the study area for with/without SAV scenarios in a carbon balance model. The total net GHG flux was in the range of −0.13 ± 0.06 to −0.86 ± 0.37 × 105 tonne CO2e y−1 and increased up to 40% (−0.23 ± 0.10 to −0.90 ± 0.39 × 105 tonne CO2e y−1) when SAV was accounted for within the calculation. At the hectare scale, the inclusion of SAV resulted in an increase of ~60% for the net GHG sink in shallow areas adjacent to the emergent marsh where SAV was abundant. This is the first attempt at remotely mapping SAV in coastal Louisiana as well as a first quantification of net GHG flux at the scale of hectares to thousands of hectares, accounting for SAV within these sub-tropical coastal delta marshes. Remote sensing and deep learning models have high potential for mapping and monitoring SAV in turbid sub-tropical coastal deltas as a component of the increasing accuracy of net GHG flux estimates at small (hectare) and large (coastal basin) scales. [ABSTRACT FROM AUTHOR]

Objective: Submerged aquatic vegetation (SAV) is an important part of shallow lake ecosystems. It provides protective cover and foraging habitat for age‐0 and juvenile Largemouth Bass Micropterus salmoides and other small fish, creates structure and habitat for macroinvertebrates and other fauna, and can influence the physical environment by stabilizing sediments and reducing water column turbidity. Methods: For this study, we reviewed annual abundance data for Largemouth Bass collected via electrofishing from 2002 to 2019, along with environmental covariates that included SAV cover (habitat) and turbidity. Result: All age‐groups of Largemouth Bass were positively correlated with vascular SAV cover. Age‐0 Largemouth Bass were most abundant when SAV cover exceeded approximately 24% (9400 ha) of the littoral and nearshore area, while the juvenile and all‐ages groups were most abundant when SAV cover exceeded 20% and 12% of the area, respectively. Following major storm events, water depth and turbidity increased, SAV cover was reduced to <5% of the littoral and nearshore area, and the abundance of age‐0 Largemouth Bass was reduced more than 90%. Conclusion: Once removed from the landscape and exposed to turbid conditions, vascular SAV will reestablish only if water clarity increases and light is sufficient to support plant growth. Lowering water levels for an extended period has been shown to reduce nearshore turbidity and jumpstart the recovery of SAV in Lake Okeechobee and other shallow lakes globally. Without adequate SAV habitat, recruitment of age‐0 and juvenile Largemouth Bass will likely be suppressed. Maintaining a minimum coverage of vascular SAV (20–35%) in the littoral and nearshore area should increase the abundance of age‐0 and juvenile Largemouth Bass and provide beneficial habitat for adult Largemouth Bass and other lake fauna. Impact statementLargemouth Bass is the most popular and targeted game fish in the United States. Submerged aquatic vegetation provides enhanced foraging habitat and protective cover for subadult Largemouth Bass that increases their abundance and rate of survival. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation (SAV) in lake littoral zones is an inland water wetland type that provides numerous essential ecosystem services, such as supplying food and habitat for fauna, regulating nutrient fluxes, stabilizing sediments, and maintaining a clear water state. However, little is known on how inland SAV quantities are changing globally in response to human activities, where loss threatens the provisioning of these ecosystem services. In this study, we generate a comprehensive global synthesis of trends in SAV quantities using time series (>10 years) in lakes and identify their main drivers. We compiled trends across methods and metrics, integrating both observational and paleolimnological approaches as well as diverse measures of SAV quantities, including areal extent, density, or abundance classes. The compilation revealed that knowledge on SAV is mostly derived from temperate regions, with major gaps in tropical, boreal, and mountainous lake‐rich regions. Similar to other wetland types, we found that 41% of SAV times series are largely decreasing mostly due to land use change and resulting eutrophication. SAV is, however, increasing in 28% of cases, primarily since the 1980s. We show that trends and drivers of SAV quantities vary regionally, with increases in Europe explained mainly by management, decreases in Asia due to eutrophication and land use change, and variable trends in North America consistent with invasive species arrival. By providing a quantitative portrait of trends in SAV quantities worldwide, we identify knowledge gaps and future SAV research priorities. By considering the drivers of different trends, we also offer insight to future lake management related to climate, positive restoration actions, and change in community structure on SAV quantities. [ABSTRACT FROM AUTHOR]

The introduction and spread of non‐native species restructure native ecosystems and can be particularly impactful when invaders are ecosystem engineers or habitat‐forming species. In coastal, estuarine, and marine systems, submerged aquatic vegetation (SAV), like macroalgae and seagrasses, form key habitats for nekton, serving as nurseries, foraging grounds, and reproduction sites. If non‐native ecosystem engineers can provide sufficient structure and/or resources, they may exert a neutral or positive effect on organisms occupying higher trophic positions. As such, we hypothesized that nekton response to non‐native SAV species may be neutral or positive. We performed a quantitative meta‐analysis to quantify impacts of non‐native SAV on native crabs, fishes, and shrimps. We extracted data from 35 studies and evaluated 11 response metrics related to facilitation (e.g., habitat use and foraging), restricting our analysis to studies that compared at least one of these metrics in nekton from co‐occurring native and non‐native SAV habitats in marine, coastal, or estuarine systems. We found that nekton abundance, species richness, and biomass were the most assessed metrics of nekton performance. Our pooled data revealed differential results among response metrics, with nekton growth and reproduction enhanced in non‐native habitats and species richness enhanced in a native setting. The mean effect sizes for all other nekton response metrics, including abundance, had 95% CIs that overlapped zero, indicating no difference in response between native and non‐native SAV. For many endpoints, limited sample sizes prevented robust inferences, but they also highlighted areas where more research is needed in future studies. Non‐native species have the potential to restructure the systems they invade. Our results lend support to the relative trophic position hypothesis, indicating that non‐native habitat formers may facilitate native organisms in higher trophic levels. We identify research gaps that may guide future studies and allow for a more comprehensive understanding of responses to non‐native ecosystem engineers. [ABSTRACT FROM AUTHOR]

Competitive interactions between native and nonindigenous species occur under conditions of ongoing environmental alterations related to urbanization and climate change, presenting a challenge to understanding invasiveness. Indigenous submerged aquatic vegetation species have been negatively impacted by nutrient enrichment and saltwater intrusion, while simultaneously experiencing a rapid spread in nonindigenous competitors. To better predict future shifts in freshwater macrophyte community dominance, investigations need to consider how these multiscale disturbances influence competitiveness of nonindigenous macrophytes. Using an outdoor greenhouse mesocosm setup for approximately 19 weeks over the course of subtropical winter, we experimentally examined how nutrient enrichment, salinity, and the interaction of both factors influence the competitive interactions between a native macrophyte with moderate salinity tolerance, wild celery (Vallisneria americana), and a highly invasive macrophyte with lower salinity tolerance, hydrilla (Hydrilla verticillata). We tested the factors of macrophyte composition (hydrilla monoculture, wild celery monoculture, or biculture), salinity (0, 4, or 8), and fertilization (ambient or fertilized) on biomass production, biomass allocation, and morphological metrics as responses to environmental condition and interspecific competition. Fertilizer enhanced wild celery leaf area (more than twofold) and shifted allocation toward aboveground biomass, but did not enhance hydrilla competitiveness. Salinity negatively affected wild celery leaf area (by 7.5%–67.8%) and biomass (by 4%–15%) and also reduced hydrilla belowground biomass production (by 6%–25%) but did not influence competition. An interaction effect of fertilizer and salinity negatively influenced hydrilla growth, however the combined factors did not influence competitive outcomes. The lack of evidence for a competitive advantage by hydrilla in this study demonstrates that salinity exposure sufficiently limits a highly invasive plant's competitive abilities and subsequent suppression of a native species. [ABSTRACT FROM AUTHOR]

In 2015, the fourth year of the recent drought, the California Department of Water Resources installed a rock barrier across False River west of Franks Tract to limit salt intrusion into the Delta at minimal cost in freshwater. This Barrier blocked flow in False River, greatly reducing landward salt transport by decreasing tidal dispersion in Franks Tract. We investigated some ecological consequences of the Barrier, examining its effects on water circulation and exchange, on distributions of submerged aquatic vegetation (SAV) and bivalves, and on phytoplankton and zooplankton. The Barrier allowed SAV to spread to areas of Franks Tract that previously had been clear. The distributions of bivalves (Potamocorbula and Corbicula) responded to the changes in salinity at time–scales of months for newly settled individuals, to 1 or more years for adults, but the Barrier’s effect was confounded with that of the drought. Nutrients, phytoplankton biomass, and a Microcystis abundance index showed little response to the Barrier. Transport of copepods — determined using output from a particle-tracking model — indicated some intermediate-scale reduction with the Barrier in place, but monitoring data did not show a larger-scale response in abundance. These studies were conducted separately and synthesized after the fact, and relied on reference conditions that were not always suitable for identifying the Barrier’s effects. If barriers are considered in the future, we rcommend a modest program of investigation to replicate study elements, and to ensure suitable reference conditions are available to allow barrier effects to be distinguished unambiguously from other sources of variability.

Abstract Seagrass meadows are one of the most important benthic habitats in the Baltic Sea. Nevertheless, spatially continuous mapping data of Zostera marina, the predominant seagrass species in the Baltic Sea, are lacking in the shallow coastal waters. Sentinel‐2 turned out to be valuable for mapping coastal benthic habitats in clear waters, whereas knowledge in turbid waters is rare. Here, we transfer a clear water mapping approach to turbid waters to assess how Sentinel‐2 can contribute to seagrass mapping in the Western Baltic Sea. Sentinel‐2 data were atmospherically corrected using ACOLITE and subsequently corrected for water column effects. To generate a data basis for training and validating random forest classification models, we developed an upscaling approach using video transect data and aerial imagery. We were able to map five coastal benthic habitats: bare sand (25 km²), sand dominated (16 km²), seagrass dominated (7 km²), dense seagrass (25 km²) and mixed substrates with red/ brown algae (3.5 km²) in a study area along the northern German coastline. Validation with independent data pointed out that water column correction does not significantly improve classification results compared to solely atmospherically corrected data (balanced overall accuracies ~0.92). Within optically shallow waters (0–4 m), per class and overall balanced accuracies (>0.82) differed marginally depending on the water depth. Overall balanced accuracy became worse (

Abstract Competitive interactions between native and nonindigenous species occur under conditions of ongoing environmental alterations related to urbanization and climate change, presenting a challenge to understanding invasiveness. Indigenous submerged aquatic vegetation species have been negatively impacted by nutrient enrichment and saltwater intrusion, while simultaneously experiencing a rapid spread in nonindigenous competitors. To better predict future shifts in freshwater macrophyte community dominance, investigations need to consider how these multiscale disturbances influence competitiveness of nonindigenous macrophytes. Using an outdoor greenhouse mesocosm setup for approximately 19 weeks over the course of subtropical winter, we experimentally examined how nutrient enrichment, salinity, and the interaction of both factors influence the competitive interactions between a native macrophyte with moderate salinity tolerance, wild celery (Vallisneria americana), and a highly invasive macrophyte with lower salinity tolerance, hydrilla (Hydrilla verticillata). We tested the factors of macrophyte composition (hydrilla monoculture, wild celery monoculture, or biculture), salinity (0, 4, or 8), and fertilization (ambient or fertilized) on biomass production, biomass allocation, and morphological metrics as responses to environmental condition and interspecific competition. Fertilizer enhanced wild celery leaf area (more than twofold) and shifted allocation toward aboveground biomass, but did not enhance hydrilla competitiveness. Salinity negatively affected wild celery leaf area (by 7.5%–67.8%) and biomass (by 4%–15%) and also reduced hydrilla belowground biomass production (by 6%–25%) but did not influence competition. An interaction effect of fertilizer and salinity negatively influenced hydrilla growth, however the combined factors did not influence competitive outcomes. The lack of evidence for a competitive advantage by hydrilla in this study demonstrates that salinity exposure sufficiently limits a highly invasive plant's competitive abilities and subsequent suppression of a native species.

Temperate lagoonal estuaries contain a mosaic of subtidal habitats including salt marsh creeks, sand, and seagrass. Studies comparing fish use of estuarine habitats have focused disproportionately on sand and seagrass habitats, and along the U.S. east coast, previous studies that have made the direct comparison between subtidal salt marsh creeks, sand, and seagrass habitats were spatially narrow in scope. Here, we performed a comprehensive comparison of fish species composition, abundance, diversity, richness, and fish lengths across subtidal salt marsh creek (upper creek and creek mouth sites), sand, and seagrass habitats within a temperate lagoonal estuary. Daytime otter trawl sampling occurred at 45 sites within Barnegat Bay (New Jersey) in April, June, August, and October during 2012–2014. Seventy species representing estuarine transients, residents, southern strays, and shelf strays were observed, and juvenile and small adult fishes dominated the collections. There were some differences in species composition between habitats, with the assemblages in upper creek and seagrass habitats being the most dissimilar. Fish abundance, diversity, and richness were often higher in creek mouth and seagrass habitats than in sand habitat. Similar to seagrass habitats, creek mouths were shallow, more saline, and contained complex physical structure (macroalgae, marsh banks). Many fishes used all habitats (e.g., bay anchovy Anchoa mitchilli), but others were partial to certain habitats (e.g., fourspine stickleback Apeltes quadracus in seagrass). This study reaffirmed that many interacting factors shape fish assemblages and demonstrated the significance of marsh creeks to the subtidal habitat mosaic of this temperate lagoonal estuary. [ABSTRACT FROM AUTHOR]

Tropical cyclones can severely disturb temperate and tropical ecosystems through damaging winds and excessive rainfall, but effects are often diverse, complex, and context-dependent. Coastal seagrass meadows are widespread, located along most temperate and tropical coastlines and often experience cyclones. Cyclone-associated damage following these events are variable, ranging from no seagrass damage to complete habitat destruction. Based on 51 studies examining cyclone effects on seagrasses, we did not uncover clear relationships between the number or severity of cyclones and declines in seagrass cover. Seagrasses were often minimally damaged following cyclones and were resilient to cyclone disturbances. When seagrass declines were reported, prolonged changes in seawater quality and plant burial were most often the causal factors. Methodological differences among studies and lack of data prior to a cyclone strike limited direct comparisons among articles. Suggestions to standardize future investigations of hurricane effects on seagrass meadows are provided. [ABSTRACT FROM AUTHOR]

Inland lakes are crucial for processing, storing, and releasing carbon dioxide (CO 2), and they play a significant role in the global carbon cycle and climate change. Studies have shown that inland lakes are mostly supersaturated in CO 2 , making them significant sources to the atmosphere. However, estimating CO 2 fluxes from inland lakes is still challenging due to large variations in surface water CO 2 partial pressure (p CO 2). Submerged aquatic vegetation (SAV) is widely found in aquatic ecosystems, especially in shallow lakes. However, their role in lake-wide carbonate chemistry has not been thoroughly investigated. Accurately measuring air-water CO 2 exchange and understanding the environmental factors that control these fluxes in vegetated ecosystems are essential for reducing uncertainties in global CO 2 emission estimates. In this study, high-resolution (3-h interval) field measurements were made along the nearshore of eastern Lake Taihu during the SAV growing seasons to examine their effects on surface water p CO 2 and air-water exchange. Our results showed evident daily variations in water chemistry and air-water fluxes. Daytime air-water CO 2 exchange switched from sinks in summer to sources in autumn. The vegetation sites were observed to be strong CO 2 sources consistently at night. The density of aquatic vegetation was found to be positively correlated with the daily range of p CO 2 , highlighting their role in regulating surface water carbonate chemistry. Negative correlations were found between water depth and surface p CO 2. These results highlight the importance of aquatic vegetation and daily variations in reducing uncertainties in carbon budgets of shallow aquatic systems. [Display omitted] • Understanding CO 2 flux from vegetated ecosystem is critical to narrow uncertainty in carbon flux. • Nearshore water dominated by aquatic vegetation is featured with evident daily p CO 2 variation. • The density of aquatic vegetation is positively correlated with the daily range of surface p CO 2. [ABSTRACT FROM AUTHOR]

Seagrasses are globally recognized for their contribution to blue carbon sequestration. However, accurate quantification of their carbon storage capacity remains uncertain due, in part, to an incomplete inventory of global seagrass extent and assessment of its temporal variability. Furthermore, seagrasses are undergoing significant decline globally, which highlights the urgent need to develop change detection techniques applicable to both the scale of loss and the spatial complexity of coastal environments. This study applied a deep learning algorithm to a 30-year time series of Landsat 5 through 8 imagery to quantify seagrass extent, leaf area index (LAI), and belowground organic carbon (BGC) in St. Joseph Bay, Florida, between 1990 and 2020. Consistent with previous field-based observations regarding stability of seagrass extent throughout St. Joseph Bay, there was no temporal trend in seagrass extent (23 ± 3 km2, τ = 0.09, p = 0.59, n = 31), LAI (1.6 ± 0.2, τ = -0.13, p = 0.42, n = 31), or BGC (165 ± 19 g C m−2, τ = - 0.01, p = 0.1, n = 31) over the 30-year study period. There were, however, six brief declines in seagrass extent between the years 2004 and 2019 following tropical cyclones, from which seagrasses recovered rapidly. Fine-scale interannual variability in seagrass extent, LAI, and BGC was unrelated to sea surface temperature or to climate variability associated with the El Niño-Southern Oscillation or the North Atlantic Oscillation. Although our temporal assessment showed that seagrass and its belowground carbon were stable in St. Joseph Bay from 1990 to 2020, forecasts suggest that environmental and climate pressures are ongoing, which highlights the importance of the method and time series presented here as a valuable tool to quantify decadal-scale variability in seagrass dynamics. Perhaps more importantly, our results can serve as a baseline against which we can monitor future change in seagrass communities and their blue carbon. [ABSTRACT FROM AUTHOR]

Shallow eutrophic lake with submerged aquatic vegetation (SAV) has high primary productivity, but its diurnal variation of CO2 flux remains unclear. Moreover, algae bloom has become a serious environmental problem; however, its effects are still unclear. Thus, monthly measurement in Lake Ulansuhai, a shallow eutrophic lake in China, was conducted throughout the ice-free period (April–October, 2019), to study monthly and diurnal variation of CO2 flux and the effects of algae bloom, SAV, and trophic state. Results show that the area with SAV (Site 1) acts as a CO2 sink during both daytime and nighttime in most months (spanning 5 months), and CO2 absorption during nighttime accounts for 25–45% of the total daily absorption. In contrast, the area with both SAV and algae (from May to September; Site 2) during whole ice-free period acts as a CO2 source during nighttime all the time, accounting for 30–100% (average of 80%) of the total daily emissions. Site 1 (without algae) during whole ice-free period acts as a net CO2 sink with CO2 flux of −7.3 ± 4.73 mmol m−2 d−1, whereas Site 2 (with algae) plays as CO2 source with CO2 flux of 5.54 ± 3.15 mmol m−2 d−1. Furthermore, monthly variation during 7 months suggests that total daily CO2 emission flux in April (after ice-melt period) at Site 1 (without algae) and Site 2 (with algae) reached 17.78 and 34.75 mmol m−2 d−1, respectively, indicating that the period plays an important role for CO2 emission budget during the whole ice-free period. Results show that the effects of algae bloom and SAV need to be paid more attention in further works. [ABSTRACT FROM AUTHOR]

Knowledge about the diversity and spatiotemporal variability of epiphytic diatom communities in estuarine meadows has great relevance for coastal ecology and, thus, contributes to understanding the impact of natural and anthropogenic changes on seagrass meadows. The community of epiphytic diatoms in Ruppia maritima L. meadows was investigated in two environments with different levels of anthropogenic impact and nutrient loads. Both impacted and non-impacted meadows had similar conditions in terms of water depth, temperature and transparency but distinct nutrient loads and salinity ranges. A total of 159 diatom taxa were found on Ruppia maritima leaves during the monitoring period, including freshwater (30.8%), marine (25.1%), brackish (9.4%) and cosmopolitan (8.8%) taxa. The most abundant species were C. placentula, T. tabulata, M. pumila and T. fasciculata, in addition to A. tenuissimus, C. adhaerens and M. moniliformis. Although present in both sites, C. placentula and T. tabulata were the dominant species in the impacted site. We found that 32% of the taxa were exclusive to the non-impacted site, 23% to the impacted site and 45% were common to both sites. The study sites showed marked differences in community attributes; i.e., higher richness, diversity and equitability and lower dominance were found in the non-impacted site, which is distant from anthropogenic sources of domestic and industrial sewage and has low concentrations of dissolved N and P in water and low values of sediment organic matter. Nutrient concentration and salinity were the main factors behind the spatial and temporal variability in the structure of the epiphytic community when all other environmental variables were similar (water depth, temperature, transparency and host plant). The influence of temperature and salinity on community structure was site-dependent. This study revealed the high richness and diversity of epiphytic diatoms in the meadows of the Patos Lagoon estuary (PLE) and the high spatial and temporal heterogeneity of the communities, and it shows the potential of epiphytic community studies for the assessment of environmental quality in seagrass meadow habitats. [ABSTRACT FROM AUTHOR]

Large rivers can retain a substantial amount of nitrogen (N), particularly in submerged aquatic vegetation (SAV) meadows that may act as disproportionate control points for N retention. However, the temporal variation of N retention in large rivers remains unknown since past measurements were snapshots in time. Using high‐frequency plants and NO3− measurements over the summers 2012–2017, we investigated how the climate variation influenced N retention in a SAV meadow (∼10 km2) at the confluence zone of two agricultural tributaries entering the St. Lawrence River. Distinctive combinations of water temperature and level were recorded between years, ranging from extreme hot‐low (2012) and cold‐high (2017) summers (2°C and 1.4 m interannual range). Using an indicator of SAV biomass, we found that these extreme hot‐low and cold‐high years had reduced biomass compared to hot summers with intermediate levels. In addition, changes in main stem water levels were asynchronous with the tributary discharges that controlled NO3− inputs at the confluence. We estimated daily N uptake rates from a moored NO3− sensor and partitioned these into assimilatory and dissimilatory pathways. Measured rates were variable but among the highest reported in rivers (median 576 mg N m−2 d−1, range 60–3,893 mg N m−2 d−1) and SAV biomass promoted greater proportional retention and permanent N loss through denitrification. We estimated that the SAV meadow could retain up to 0.8 kt N per year and 87% of N inputs, but this valuable ecosystem service is contingent on how climate variations modulate both N loads and SAV biomass. Plain Language Summary: Large rivers remove significant amounts of nitrogen pollution generated by humans in waste waters and from fertilizers applied to agricultural lands. Underwater meadows of aquatic plants remove nitrogen particularly well. To keep the river clean, plants use the nitrogen themselves and promote conditions where bacteria can convert this pollution into a gas typically found in air. Measuring nitrogen removal in rivers is really difficult, and we do not know how climate conditions influence this removal or plant abundance. We successfully measured nitrogen pollution removal from an underwater plant meadow in a large river over six summers. We found that plant abundance and river nitrogen inputs were critical to determine how much pollution was removed, and that these were controlled by climatic conditions. Plant abundance was controlled by both water temperatures and levels. When water was warm and levels were neither too high nor too low, conditions were perfect for lots of plants to grow, which mainly stimulated bacteria that permanently eliminated nitrogen. We showed that the amount of nitrogen pollution removed over the summer by the meadow changes with climatic conditions but in general represents the amount produced by a city of half a million people. Key Points: Nitrogen retention and biomass were measured at a high resolution over six summers in a submerged aquatic vegetation meadow of a large riverAmong the highest riverine, nitrate uptake rates were recorded, and 47%–87% of loads were retained with plants favoring denitrificationInterannual climate variations influenced nitrate retention by altering water levels, temperature, plant biomass, and tributary nitrate load [ABSTRACT FROM AUTHOR]

Potamogeton illinoensis is a North American macrophyte, commonly the focus of management, but limited knowledge of its life history hampers conservation and restoration efforts. We conducted greenhouse and growth chamber experiments and field monitoring to understand intraspecific variation in P. illinoensis reproduction and germination traits, monitoring one restored and three natural populations in Central Florida, USA. We assessed reproductive phenology, seed banks in the fall and spring, and germination across different light, temperature, sediment, and ethylene treatments. Flowering and seeding occurred spring through fall, with the highest seed bank densities in fall and minimal seeds detected in late spring. Seeds germinated at the highest percentages in light from 20 to 25°C, and at higher percentages in highly organic field-collected soil. Seeds treated with ethephon, which emits ethylene (commonly produced by submerged organic sediments), germinated at nearly twice the percentage as those exposed to water alone. While these reproductive and germination patterns were true across populations, there was variation among populations in seed bank densities, the most favorable germination temperatures, and overall germination percentages, indicating population differences contribute to reproductive performance. These results suggest restoration via seeds will be limited in conditions with low light or in unconsolidated sediments where burial is likely. [ABSTRACT FROM AUTHOR]

Mediterranean salinas, originally built for salt production, function as alternative wetlands. A variety of accompanying lagoon, ditch, and marsh systems are suitable habitats for salt-tolerant submerged macrophytes and often characterized by monospecific beds of Ruppia. Traditionally, birds are considered the main dispersal vector of submerged macrophytes. However, Ruppia spiralis habitats are under marine influence and therefore interference of coastal currents in their connectivity might be expected. In this study, we aim to infer connectivity and spatial patterns from population genetic structures. Using nuclear microsatellite loci, the nuclear ribosomal cistron and chloroplast sequences, we investigated the genetic diversity, genetic structure, and demographic history of 10 R. spiralis populations along a 25-km coastal stretch of western Sicily encompassing a variety of saline habitats. We tested for local fine-scaled structures, hypotheses of regional isolation by distance, and migration directionality. Our results revealed a high degree of allele and gene diversity that was locally maintained by outcrossing. At the regional level, we detected isolation by distance and identified three genetically differentiated clusters, with a significant structure that matches an overall north-to-south unidirectional migration model. This directionality follows the main sea current, hence indicating the importance of hydrological connectivity in regional conservation management. Significant fine-scale spatial structures only emerged in some populations and were absent in the ‘salina fridda’ habitat that showed the largest clonal richness. The local site-dependent patterns emphasize a need to examine the influence of disturbances on seed recruitment and clonal growth over small distances.

Submerged aquatic vegetation (SAV) are highly efficient at carbon sequestration and, despite their relatively small distribution globally, are recognized as a potentially valuable component of climate change mitigation. However, SAV mapping in tidal marshes presents a challenge due to optically complex constituents in the water. The emergence and advancement of deep learning-based techniques in the field of habitat mapping with remote sensing imagery provides an opportunity to address this challenge. In this study, an analytical framework was developed to quantify the carbon sequestration of SAV habitats in the Atchafalaya River Delta Estuary from field and remote sensing observations using deep convolutional neural network (DCNN) techniques. A U-Net-based model, Wetland-SAV Network, was trained to identify the SAV percent cover (high, medium, and low) as well as other estuarine habitat types from Landsat 8/9-OLI data. The areal extent of SAV was up to 8% of the total area (47,000 ha). The habitat areas and habitat-specific carbon fluxes were then used to quantify the net greenhouse gas (GHG) flux of the study area for with/without SAV scenarios in a carbon balance model. The total net GHG flux was in the range of −0.13 ± 0.06 to −0.86 ± 0.37 × 105 tonne CO2e y−1 and increased up to 40% (−0.23 ± 0.10 to −0.90 ± 0.39 × 105 tonne CO2e y−1) when SAV was accounted for within the calculation. At the hectare scale, the inclusion of SAV resulted in an increase of ~60% for the net GHG sink in shallow areas adjacent to the emergent marsh where SAV was abundant. This is the first attempt at remotely mapping SAV in coastal Louisiana as well as a first quantification of net GHG flux at the scale of hectares to thousands of hectares, accounting for SAV within these sub-tropical coastal delta marshes. Remote sensing and deep learning models have high potential for mapping and monitoring SAV in turbid sub-tropical coastal deltas as a component of the increasing accuracy of net GHG flux estimates at small (hectare) and large (coastal basin) scales.

Research on aquatic plant viruses is lagging behind that of their terrestrial counterparts. To address this knowledge gap, here we identified viruses associated with freshwater macrophytes, a taxonomically diverse group of aquatic phototrophs that are visible with the naked eye. We surveyed pooled macrophyte samples collected at four spring sites in Florida, USA through next generation sequencing of RNA extracted from purified viral particles. Sequencing efforts resulted in the detection of 156 freshwater macrophyte associated (FMA) viral contigs, 37 of which approximate complete genomes or segments. FMA viral contigs represent putative members from all five major phyla of the RNA viral kingdom Orthornavirae. Similar to viral types found in land plants, viral sequences identified in macrophytes were dominated by positive-sense RNA viruses. Over half of the FMA viral contigs were most similar to viruses reported from diverse hosts in aquatic environments, including phototrophs, invertebrates, and fungi. The detection of FMA viruses from orders dominated by plant viruses, namely Patatavirales and Tymovirales, indicate that members of these orders may thrive in aquatic hosts. PCR assays confirmed the presence of putative FMA plant viruses in asymptomatic vascular plants, indicating that viruses with persistent lifestyles are widespread in macrophytes. The detection of potato virus Y and oat blue dwarf virus in submerged macrophytes suggests that terrestrial plant viruses infect underwater plants and highlights a potential terrestrial-freshwater plant virus continuum. Defining the virome of unexplored macrophytes will improve our understanding of virus evolution in terrestrial and aquatic primary producers and reveal the potential ecological impacts of viral infection in macrophytes. [ABSTRACT FROM AUTHOR]

Coastal waters are highly productive and diverse ecosystems, often dominated by marine submerged aquatic vegetation (SAV) and strongly affected by a range of human pressures. Due to their important ecosystem functions, for decades, both researchers and managers have investigated changes in SAV abundance and growth dynamics to understand linkages to human perturbations. In European coastal waters, monitoring of marine SAV communities traditionally combines diver observations and/or video recordings to determine, for example, spatial coverage and species composition. While these techniques provide very useful data, they are rather time consuming, labor‐intensive, and limited in their spatial coverage. In this study, we compare traditional and emerging remote sensing technologies used to monitor marine SAV, which include satellite and occupied aircraft operations, aerial drones, and acoustics. We introduce these techniques and identify their main strengths and limitations. Finally, we provide recommendations for researchers and managers to choose the appropriate techniques for future surveys and monitoring programs. Integr Environ Assess Manag 2022;18:892–908. © 2021 SETAC Key Points: No technology is perfect; the monitoring objectives, data needs, and budget therefore should be known before the preferred technique is chosen.Studies should combine the different technologies as well as increase the use of machine learning for post processing of the obtained data. [ABSTRACT FROM AUTHOR]

Seagrass meadows are one of the most important benthic habitats in the Baltic Sea. Nevertheless, spatially continuous mapping data of Zostera marina, the predominant seagrass species in the Baltic Sea, are lacking in the shallow coastal waters. Sentinel‐2 turned out to be valuable for mapping coastal benthic habitats in clear waters, whereas knowledge in turbid waters is rare. Here, we transfer a clear water mapping approach to turbid waters to assess how Sentinel‐2 can contribute to seagrass mapping in the Western Baltic Sea. Sentinel‐2 data were atmospherically corrected using ACOLITE and subsequently corrected for water column effects. To generate a data basis for training and validating random forest classification models, we developed an upscaling approach using video transect data and aerial imagery. We were able to map five coastal benthic habitats: bare sand (25 km²), sand dominated (16 km²), seagrass dominated (7 km²), dense seagrass (25 km²) and mixed substrates with red/ brown algae (3.5 km²) in a study area along the northern German coastline. Validation with independent data pointed out that water column correction does not significantly improve classification results compared to solely atmospherically corrected data (balanced overall accuracies ~0.92). Within optically shallow waters (0–4 m), per class and overall balanced accuracies (>0.82) differed marginally depending on the water depth. Overall balanced accuracy became worse (<0.8) approaching the border to optically deep water (~ 5 m). The spatial resolution of Sentinel‐2 (10–20 m) allowed delineating detailed spatial patterns of seagrass habitats, which may serve as a basis to retrieve spatially continuous data for ecologically relevant metrics such as patchiness. Thus, Sentinel‐2 can contribute unprecedented information for seagrass mapping between 0 and around 5 m water depths in the Western Baltic Sea. [ABSTRACT FROM AUTHOR]

Measured decreases in the spatial extent of seagrasses in Massachusetts are attributed to declining water quality, disease, or direct and indirect impact from dredging or construction. Routine aerial monitoring of seagrasses along the 2400-km coastline is costly and therefore limited both temporally and spatially. Diver surveys are used at two sites for in situ assessments of seagrass meadow structure. In order to examine spatial and temporal trends in seagrass extent and structure, a survey methodology that is less expensive and better at capturing structural characteristics than aerial photography and more efficient than divers is needed. Hydroacoustic methods are relatively inexpensive and rapidly deployed and can measure characteristics including canopy height and percent cover of eelgrass meadows. We tested the capabilities and limitations of a BioSonics DT-X echosounder using the EcoSAV algorithm to measure presence/absence, canopy height, and percent cover of eelgrass. Measurements were found to be reproducible on duplicate transects but had low precision: 36 cm for canopy height and 34% for percent cover. To assess accuracy, we compared EcoSAV estimates of canopy height and percent cover with diver measurements. The EcoSAV estimates of canopy height and percent cover were significantly higher than diver measurements by 60 cm and 46%. We conclude that the BioSonics with EcoSAV processing is an efficient tool to map eelgrass meadows and assess relative change over time, but because of differences in the way the echosounder measurements are made compared with diver measurements, echosounder data should not be used to directly compare with diver data or for surveys that require high accuracy and precision. [ABSTRACT FROM AUTHOR]

Research on aquatic plant viruses is lagging behind that of their terrestrial counterparts. To address this knowledge gap, here we identified viruses associated with freshwater macrophytes, a taxonomically diverse group of aquatic phototrophs that are visible with the naked eye. We surveyed pooled macrophyte samples collected at four spring sites in Florida, USA through next generation sequencing of RNA extracted from purified viral particles. Sequencing efforts resulted in the detection of 156 freshwater macrophyte associated (FMA) viral contigs, 37 of which approximate complete genomes or segments. FMA viral contigs represent putative members from all five major phyla of the RNA viral kingdom Orthornavirae. Similar to viral types found in land plants, viral sequences identified in macrophytes were dominated by positive-sense RNA viruses. Over half of the FMA viral contigs were most similar to viruses reported from diverse hosts in aquatic environments, including phototrophs, invertebrates, and fungi. The detection of FMA viruses from orders dominated by plant viruses, namely Patatavirales and Tymovirales, indicate that members of these orders may thrive in aquatic hosts. PCR assays confirmed the presence of putative FMA plant viruses in asymptomatic vascular plants, indicating that viruses with persistent lifestyles are widespread in macrophytes. The detection of potato virus Y and oat blue dwarf virus in submerged macrophytes suggests that terrestrial plant viruses infect underwater plants and highlights a potential terrestrial-freshwater plant virus continuum. Defining the virome of unexplored macrophytes will improve our understanding of virus evolution in terrestrial and aquatic primary producers and reveal the potential ecological impacts of viral infection in macrophytes.

Submerged plants play a significant role in the remediation and purification of polluted water bodies. Reconstruction of submerged plants has been considered as an important ecological method to restore aquatic ecosystems. However, large-scale and efficient plantation of submerged plants in water restoration is a huge challenge. This paper proposes a novel mechanized planting method for submerged plants utilizing nutrition pots as planting units. Firstly, the details of the mechanized planting method were introduced. The mechanized planting method involves pre-planting the reproductive bodies of submerged plants in degradable nutrition pots, and then implanting them into the underwater soil through a planting device. Secondly, the interaction force between the nutrition pot and the soil was measured. It was found that the implantation force of nutrition pots increases with planting velocity. The planting force shows a significant increase trend when the water content in the soil decreases. Thirdly, the deformation of the nutrition pot was studied through simulations. It was discovered that the deformation of the nutrition pot mainly occurs at the bottom and the side walls near the bottom, and the limited deformation ensures the integrity of the nutrition pot. Finally, a planting device with a linear motion mechanism was designed, and a typical submerged plant, Vallisneria natans was tested, using agricultural paper seedling containers as the nutrition pots. It was demonstrated that the mechanized device successfully planted submerged plant nutrition pots into the soil, and the submerged plants survived and showed a clear growth trend. The mechanized planting method of submerged plants proposed in this article is expected to provide a new and friendly technology for ecological restoration of water source. [Display omitted] • A mechanized planting method for submerged plants in water ecological restoration is reported. • The interaction force between the nutrition pot and the soil was measured using force sensors. • A planting device was designed for the high-efficiency planting of submerged plants. • The planting method is expected to offer a technology for large-scale water ecological restoration. [ABSTRACT FROM AUTHOR]

Managed treatment wetlands technology is now used around the world to treat wastewater and stormwater by removing nutrients and other contaminants to obtain a desired water quality. In this paper we present a brief review of a large-scale application of the nature-based technology known as stormwater treatment areas (STAs). These STAs were constructed to treat agricultural and urban runoff to reduce outflow total phosphorus (TP) concentrations to <20 μg P L−1, which is required to protect downstream water quality and preserve the remaining Everglades ecosystem. Five STAs with a total area of approximately 25,000 ha were built at strategic locations to reduce TP loads to the Everglades Protection Area. For the past three decades, these Everglades STAs have done remarkable job by 70 to 85% TP load reduction, with an average outflow TP concentrations of 15-40 μg P L−1. In this Everglades STAs special issue, we present research findings on the influence of both external and internal drivers influencing STA performance and potential adaptive management strategies to enhance treatment efficiency to further reduce outflow TP concentrations. • Introduction of the Everglades STAs – largest constructed treatment wetland network in the world. • Everglades STAs serve as 'kidneys' of the Everglades ecosystem by reducing phosphorus loads to downstream waterbodies. • Phosphorus loading is one of the key drivers regulating treatment efficiency STAs. [ABSTRACT FROM AUTHOR]

Traditional remote sensing methods are rarely applied to headwater streams because of a mismatch in spatial scale. With improved technology, remote sensing using unoccupied aerial vehicles enables imagery to be collected at high spatial and temporal resolution. However, these innovations have been used less frequently to detect changes within the water column. In addition, it is unclear whether classification methods developed along a single reach can be transferred through space (to other reaches) and through time, or how much information is needed to perform such classifications. This study combines methods of remote sensing, image processing, and machine learning to classify land cover and submerged aquatic vegetation along four urban stream reaches (170–325 m). A linear discriminant analysis (LDA) model was developed to provide land and water cover classification maps using training data. This method proved to be robust when classifying land cover along a single reach with minimal training data required. Using 200 pixels per land cover class resulted in 100% classification confidence for more than 93% of the pixels; when reducing this to only 50 pixels per land cover class, LDA yielded 100% classification confidence for nearly 80% of the total pixels. Through attempts to transfer relationships across reaches and flight dates, we found a greater percentage of misclassified pixels (upwards of 45% misclassification for flights on one date) when classifying across reaches on a single date as opposed to classification along a single reach for multiple dates. Overall, we recommend passive optical approaches, like the one used here, consider lighting conditions, reach orientation, and shading in data acquisition planning to mitigate the uncertainty they may introduce in delineating water column quality and cover. [ABSTRACT FROM AUTHOR]

Lake Burullus is the second largest lake at the northern edge of the Nile Delta, Egypt, and has been recognized as an internationally significant wetland that provides a habitat for migrating birds, fish, herpetofauna, and mammals. However, the lake is experiencing severe human impacts including drainage and conversion to agricultural lands and fish farms. The primary goal of this study was to use multispectral, moderate-spatial-resolution (30 m2) Landsat satellite imagery to assess marsh loss in Lake Burullus, Egypt, in the last 35 years (1985–2020). Iterative Self-Organizing Data Analyses (ISODATA) unsupervised techniques were applied to the Landsat 5 Thematic Mapper (TM) and Landsat 8 Operational Land Imager–Thermal Infrared Sensor (OLI–TIRS) satellite images for classification of the Lake Burullus area into four main land-use classes: water, marsh, unvegetated land surfaces (roads, paths, sand sheets and dunes), and agricultural lands and fish farms. The overall classification accuracy was estimated to be 96% and the Kappa index was 0.95. Our results indicated that there is a substantial loss (44.8% loss) in the marsh aerial coverage between 1985 and 2020. The drainage and conversion of wetlands into agricultural lands and/or fish farms is concentrated primarily in the western and southern part of the lake where the surface area of the agricultural lands and/or fish farms doubled (103.2% increase) between 2000 and 2020. We recommend that land-use-policy makers and environmental government agencies raise public awareness among the local communities of Lake Burullus of the economic and environmental consequences of the alarming loss of marshland, which will likely have adverse effects on water quality and cause a reduction in the invaluable wetland-ecosystem services. [ABSTRACT FROM AUTHOR]

A warming climate is driving the poleward expansion of tropical, subtropical, and temperate plant and animal distributions. These changes have and continue to lead to the colonization of novel organisms into areas beyond their historical ranges. While the full scope of ecological impacts remains unclear, these expansions could alter density-dependent interactions, habitat occupancy patterns, and food web dynamics– similar to exotic species impacts in invaded ecosystems. Seagrasses are habitats of particular interest, given their widespread distribution and ecosystem services. While multiple recent studies report on the effects of the return of larger tropical herbivores in seagrass beds in warming subtropical waters, less is known about the addition of mid-trophic level consumers. These consumers are often key determinants of energy and nutrient transfers from basal resources to higher order predators. Here, we discuss the potential impacts of these distribution changes on temperate and subtropical seagrass communities using information derived from invasive species studies. Notably, we outline several scenarios and generate predictions about how their establishment might occur and speculate on impacts of warmer water consumers as they move poleward. We also discuss potential confounding factors of detecting changes in these consumer distributions. Following the invasive species literature, we offer a framework for generating hypotheses and predicting effects from these range-expanding organisms. Given that climates are predicted to continue to warm into the future, thus facilitating additional species expansions, our goal is to guide future research efforts and provide information for rapid dissemination and utility for this growing subdiscipline of marine ecology.

Processes of spread and patterns of persistence of invasive species affect species and communities in the new environment. Predicting future rates of spread is of great interest for timely management decisions, but this depends on models that rely on understanding the processes of invasion and historic observations of spread and persistence. Unfortunately, the rates of spread and patterns of persistence are difficult to model or directly observe, especially when multiple rates of spread and diverse persistence patterns may be co-occurring over the geographic distribution of the invaded ecosystem. Remote sensing systematically acquires data over large areas at fine spatial and spectral resolutions over multiple time periods that can be used to quantify spread processes and persistence patterns. We used airborne imaging spectroscopy data acquired once a year for 5 years from 2004 to 2008 to map an invaded submerged aquatic vegetation (SAV) community across 2220 km2 of waterways in the Sacramento-San Joaquin River Delta, California, USA, and measured its spread rate and its persistence. Submerged aquatic vegetation covered 13-23 km2 of the waterways (6-11%) every year. Yearly new growth accounted for 40-60% of the SAV area, ~50% of which survived to following year. Spread rates were overall negative and persistence decreased with time. From this dataset, we were able to identify both radial and saltatorial spread of the invaded SAV in the entire extent of the Delta over time. With both decreasing spread rate and persistence, it is possible that over time the invasion of this SAV community could decrease its ecological impact. A landscape-scale approach allows measurements of all invasion fronts and the spatial anisotropies associated with spread processes and persistence patterns, without spatial interpolation, at locations both proximate and distant to the focus of invasion at multiple points in time.

This paper reviews and highlights recent research findings on food web processes since an earlier review by Kimmerer et al. (2008). We conduct this review within a conceptual framework of the Delta–Suisun food web, which includes both temporal and spatial components. The temporal component of our framework is based on knowledge that the landscape has changed markedly from historical conditions. The spatial component of our framework acknowledges that the food web is not spatially static; it varies regionally and across habitat types within regions. The review highlights the idea of a changing baseline with respect to food web function. New research also indicates that interactions between habitat-specific food webs vary across the current landscape. For example, based on early work in the south Delta, the food web associated with submerged aquatic vegetation was thought to provide little support to species of concern; however, data from other regions of the estuary suggest that this conceptual model may not apply across the entire region. Habitat restoration has been proposed as a method of re-establishing historic food web processes to support species of concern. Benefits are likely for species that directly access such restored habitats, but are less clear for pelagic species. Several topics require attention to further improve the knowledge of food webs needed to support effective management, including: (1) synthesis of factors responsible for low pelagic biomass; (2) monitoring and research on effects of harmful algal blooms; (3) broadening the scope of long-term monitoring; (4) determining benefits of tidal wetland restoration to species of concern, including evaluations of interactions of habitat-specific food webs; and (5) interdisciplinary analysis and synthesis. The only certainty is that food webs will continue to change in response to the changes in the physical environment and new species invasions.

Stocking locations for grass carp introductions were selected using rake toss surveys to confirm I Hydrilla i presence, qualitative visual observations and hydroacoustic surveys to determine relative I Hydrilla i density in different coves. Keywords: American coot; bald eagle; biological control; hydrilla; submerged aquatic vegetation; vacuolar myelinopathy EN American coot bald eagle biological control hydrilla submerged aquatic vegetation vacuolar myelinopathy 100 103 4 01/12/22 20220201 NES 220201 Sterile triploid grass carp I Ctenopharyngodon Idella i (Val.) The goal of this study was to evaluate the post-stocking movement of grass carp in large reservoirs and ultimately understand the efficacy of using grass carp to control and/or eliminate I Hydrilla i and AVM disease. [Extracted from the article]