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Abstract Back Bay, Virginia, has been documented as an important foraging area for waterfowl since at least the mid‐1800s. Expansive submerged plant beds historically supported diverse assemblages of non‐breeding waterfowl; however, coastal development and other anthropogenic influences have since led to fluctuations in submerged aquatic vegetation (SAV) and an associated decline in waterfowl abundance in the bay. To gain insight into the effects of environmental drivers on waterfowl foraging guilds, our study explores the effects of SAV frequency and water quality on the abundance of dabbling ducks, diving ducks and swans and geese in Back Bay. We use 8 years of SAV, water quality, and waterfowl monitoring data collected by state and federal agencies to model the effects of salinity, turbidity, pH and percent frequency of SAV on the relative abundance of waterfowl by foraging guild in Back Bay. The appropriateness of the data and reasonability of the preliminary results were then evaluated through semi‐structured interviews with 11 local informants representing state, federal and non‐governmental organizations. Quantitative results indicated that dabbling ducks are affected differently than other guilds by water quality and percent frequency of SAV. Thematic analysis of the interview data revealed a number of potential explanations for the model results, as well as highlighted areas of uncertainty in need of further research. In a test of face validity, participants demonstrated a significant degree of belief in turbidity, salinity and SAV as drivers of waterfowl abundance, but were not convinced by the potential effects of pH as demonstrated by the model. This mixed methods study provides insights that could potentially influence the management and conservation of non‐breeding waterfowl populations by challenging the assumption that particular environmental conditions serve all foraging groups equally.

Wet carbon (WC) ecosystems are a critical part of the carbon cycle, yet they are underrepresented in many policy and science communities due to the relative under-investment in stakeholder and boundary organizations. WC systems include the hydrosphere and carbon cycling systems that operate in wetlands, oceans, rivers, streams, lakes, ponds, and permafrost. In this article, we provide evidence from a desk review of WC stakeholders, that includes individuals, groups or organizations that are affected by climate change, and utilize carbon data. These stakeholders are involved in decision-making processes in WC ecosystems, and can be private companies, non-governmental organizations, government agencies ranging in scope from local to federal, parastatals, international organizations, and more. In this paper, we identify and describe the links and interests of WC stakeholders and analyze the gaps between scientific understanding and information needs. A continued focus on WC systems could lead to increased stakeholder engagement and methodological and scientific progress. Our study revealed that stakeholder interest in WC systems was not primarily determined by its role in the carbon cycle, but rather by its significance for local policy, economics, or ecology. To bridge the gap between stakeholders and available WC data, we need improved communication of data availability and uncertainty, capacity building, engagement between stakeholder groups, and data continuity. Enhanced stakeholder engagement across various systems will facilitate greater utilization of carbon monitoring data derived from remote sensing; thereby creating more informed stakeholders as well as more effective decision-making processes.

The increasing use of artificial light at night has led to ecosystem exposure to light pollution worldwide. Aquatic ecosystems are particularly exposed, since lit road networks, urban development and industrial infrastructure are frequently located along river, lake, and sea shores. Although the negative effects of night‐time lighting on the physiology, behaviour, and life‐history traits of animals have been largely documented, there is a large knowledge gap about the responses of plants, especially regarding leaf functioning and resource‐management strategies. Some authors have proposed contrasting hypotheses of mechanistic responses to dim light at night in plants, but empirical results are still lacking.Based on field measurements of nocturnal irradiance in freshwater ecosystems located in peri‐urban areas, we performed a mesocosm experiment using three species of submerged aquatic plants. After 5 months of exposure to realistic dim light at night, four functional traits related to the resource management at the leaf level were measured.Artificial light at night had significant effects on the leaf physiology or chemistry, affecting their resource acquisition rate, but with different response intensities depending on the species. No effect was found on morphological or biomechanical traits for any of the studied species.These results support the hypothesis that plants could interpret dim light at night as a shaded environment and respond accordingly.We demonstrated that the effects of light at night on plants may have been underestimated in previous work. By modifying biotic interactions (e.g., competition and herbivory), these responses can have profound effects on community structure and ecosystem functioning. [ABSTRACT FROM AUTHOR]

The Everglades Stormwater Treatment Areas (STAs) are a complex of large constructed wetlands that are an integral component of the State and Federal efforts to restore the Everglades ecosystem. The overall objective of this study was to determine the accumulation rates of macro‐elements including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and associated secondary elements including calcium (Ca), magnesium (Mg), aluminum (Al), and iron (Fe) in two Everglades STAs over their periods of operation. The study was conducted in STA‐2 with parallel flow‐ways consisting of emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) and the Western flow‐way of STA‐3/4 with EAV and SAV cells operated in series. Elemental accumulation rates were determined in the unconsolidated surficial sediments (floc) and recently accreted soil (RAS) that have accumulated on top of the antecedent soil over the 14‐ and 10‐yr periods of operation for STA‐2 and STA‐3/4, respectively. Flow‐ways with SAV were more efficient than EAV in accreting mineral matter, resulting in increased bulk density and higher accumulation rates of elements. Average C accumulation in the floc and RAS of SAV flow‐ways was 320 g·m−2·yr−1 with approximately equal proportions of inorganic and organic C, while in the EAV flow‐ways accumulation rates of C ranged from 116 to 147 g·m−2·yr−1 with mostly organic C. Phosphorus accumulation rates were approximately 2–3 times higher in SAV than in EAV flow‐ways. Differences in accumulation of elements between SAV and EAV were largest for Ca with 17–42 times more Ca in SAV than EAV systems. This suggests that in the SAV systems, possible occlusion of macro‐elements and metals during CaCO3 precipitation facilitated accretion of material with high mineral content. In EAV, biomass turnover and associated biotic processes regulated organic matter accumulation rates. The spatial accumulation patterns of P, C, and N in the EAV areas of STA‐2 and STA‐3/4 were similar to those observed in the EAV areas of the natural wetlands in Water Conservation Areas, suggesting that constructed wetland systems function similarly to natural wetlands dominated by EAV areas in retaining and storing macro‐ and secondary elements. [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]

Elevated mercury (Hg) levels in biota is one issue facing the Everglades ecosystem in south Florida, USA. Methylmercury (MeHg) is a concern in the environment because it bioaccumulates through the food web and can harm fauna and humans if ingested through contaminated food sources (e.g., fish). Total mercury (THg) and MeHg concentrations were measured in several common macrophyte species, periphyton, and detritus in the Everglades to investigate Hg concentrations spatially and among different ecosystem components. At each site, two species from the carnivorous genus Utricularia , U. purpurea and U. foliosa , which are widespread and abundant in Everglades sloughs, had much higher average tissue MeHg concentrations (2.4–81 ng/g dry weight [dw]) than all other sampled macrophytes (<1.5–7.5 ng/g dw), periphyton (0.4–6.2 ng/g dw), and detritus (<1.5–5.7 ng/g dw). The Utricularia species were likewise enriched with THg (14.6–115 ng/g dw) compared to the other macrophytes (2.6–27 ng/g dw), although slough detritus had the highest THg at most sites (24–182 ng/g dw). The Utricularia species generally had a higher average percent of THg as MeHg (8.2–75%) compared to the other macrophytes, periphyton, and detritus (0–32%). MeHg concentrations in Utricularia species were quite variable among sites with a spatial distribution that generally reflected historical Hg concentration patterns known in mosquitofish (Gambusia holbrooki). Utricularia species merit further investigation to understand how they accumulate relatively high MeHg concentrations and how they might influence Hg accumulation up the food web. • Methylmercury (MeHg) contamination is prevalent in the Everglades, USA. • Utricularia spp. had higher MeHg than other macrophytes, periphyton, and detritus. • Utricularia spp. MeHg may impact the Everglades food web. • Mode of MeHg generation or uptake in Utricularia spp. needs to be investigated. [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.

Annual and perennial populations commonly occur for the same submerged aquatic angiosperm species, yet relationships between population types and sediment characteristics are poorly understood. In the current study two Ruppia sinensis habitats with annual and perennial populations were surveyed in the Yellow River Delta (YRD). Biomass and seasonal seed bank size were used to evaluate population status and potential recruitment capacity. Sediment geochemical parameters including moisture, sulfide, Chl a, carbohydrate, OM, TOC, TN, and TP were measured to compare sediment nutrient composition and variability. The results revealed a higher biomass and larger seed bank in the annual R. sinensis population compared with the perennial population. The P levels in sediments between the two R. sinensis populations were similar; while the N level in the sediment of the annual population was significantly higher than the perennial population, which might support the recruitment of vegetative shoots when a large amount of seeds germinated during wet periods. The annual population exhibited greater resilience after habitat desiccation, with the population recovering rapidly once water appeared. The results of this study add to the knowledge of R. sinensis populations and their sediment geochemical characteristics, and can be used as a reference for Ruppia population conservation and management.

Annual and perennial populations commonly occur for the same submerged aquatic angiosperm species, yet relationships between population types and sediment characteristics are poorly understood. In the current study two Ruppia sinensis habitats with annual and perennial populations were surveyed in the Yellow River Delta (YRD). Biomass and seasonal seed bank size were used to evaluate population status and potential recruitment capacity. Sediment geochemical parameters including moisture, sulfide, Chl a , carbohydrate, OM, TOC, TN, and TP were measured to compare sediment nutrient composition and variability. The results revealed a higher biomass and larger seed bank in the annual R. sinensis population compared with the perennial population. The P levels in sediments between the two R. sinensis populations were similar; while the N level in the sediment of the annual population was significantly higher than the perennial population, which might support the recruitment of vegetative shoots when a large amount of seeds germinated during wet periods. The annual population exhibited greater resilience after habitat desiccation, with the population recovering rapidly once water appeared. The results of this study add to the knowledge of R. sinensis populations and their sediment geochemical characteristics, and can be used as a reference for Ruppia population conservation and management. [ABSTRACT FROM AUTHOR]

Although shear layers generated by submerged vegetation reach a steady state once production and dissipation are balanced within a canopy, shear layers found in gaps and after trailing edges of canopy patches are inherently different and thereby perturb the canopy's mean and turbulent fields. Experiments were conducted in a laboratory flume to study canopy systems in which two model patches of submerged, rigid cylinder arrays are interrupted by a gap of varying stream‐wise lengths. Results show that, consistent with past studies, gaps locally enhance turbulence. However, this perturbation does not remain "local" within the gap, instead introducing enhanced turbulent energies throughout the water column that are transported downstream and thereby perturb the canopy flow. The study suggests a scaling, E=H−hcqU2L2, which compares the eddy turnover time of the turbulence produced by the gap to the advection time downstream the second patch, that can be used to predict if turbulence perturbations induced by an upstream gap will influence the turbulence at a given distance downstream. Key Points: Different lengths of canopy patches, if shorter than for fully developed canopy flow, introduce varying levels of turbulence to its wakeGaps locally enhance and redistribute turbulence throughout the water columnThe length of the gap has the greatest influence on the level of turbulence and flow disturbance to the downstream canopy patchTurbulence enhancements formed locally within gaps disrupt canopy flows by transporting and propagating downstream to nonlocally enhance turbulence [ABSTRACT FROM AUTHOR]

Sentinel-2 satellite imagery has been successfully used to map submerged seagrasses in clear waters, and surface-canopy forming seaweed habitats in a range of water types. We examined the ability to use Sentinel-2 remote sensing reflectance to classify fully submerged seagrass and seaweed habitats in optically complex, temperate waters within a high priority management region in Atlantic Canada. To do so, we determined the “best” Sentinel-2 image available between 2015 and 2019 based on tidal height, absence of sun glint and clouds, and water transparency. Using the full Sentinel-2 tile, we atmospherically corrected the image using ACOLITE’s dark spectrum fitting method. Our classification goal was a two-class prediction of vegetation presence and absence. Using information obtained from drop-camera surveys, the image was first partially classified using simple band thresholds based on the normalized difference vegetation index (NDVI), red/green ratio and the blue band. A random forest model was built to classify the remaining areas to a maximum depth of 10 m, the maximum depth at which field surveys were performed. The resulting habitat map had an overall accuracy of 79% and ∼231 km2 of vegetated habitat were predicted to occur (total area 345.15 km2). As expected, the classification performed best in regions dominated by bright sandy bare substrate, and dense dark vegetated beds. The classification performed less well in regions dominated by dark bare muddy substrate, whose spectra were similar to vegetated habitat, in pixels where vegetation density was low and mixed with other substrates, and in regions impacted by freshwater input. The maximum depth that bottom habitat was detectable also varied across the image. Leveraging the full capacity of the freely available Sentinel-2 satellite series with its high spatial resolution and resampling frequency, provides a new opportunity to generate large scale vegetation habitat maps, and examine how vegetation extent changes over time in Atlantic Canada, providing essential data layers to inform monitoring and management of macrophyte dominated habitats and the resulting ecosystem functions and services.

This new 9-page factsheet describes the defining characteristics of the eleven pondweed species that are present in Florida. It serves as a pondweed identification guide for aquatic habitat managers, lake monitors, conservationists, and plant enthusiasts, and it gives some context on each species’ life history and ecological role. Written by Christine Rohal, Laura Reynolds, Carrie Reinhardt Adams, and Charles Martin, and published by the UF/IFAS Department of Soil and Water Sciences. https://edis.ifas.ufl.edu/ss686

Submerged aquatic vegetation has numerous benefits for aquatic ecosystems, from improving water quality to providing important habitat that supports a diverse food web. This new 6-page publication of the UF/IFAS Department of Soil and Water Sciences describes the breadth of options available to managers who wish to plant SAV at new locations. Because all methods have both benefits and drawbacks, and because all planting locations have different (often unknown) challenges for plant survival, managers may choose to try multiple methods to increase the likelihood for success. Written by Laura Reynolds, Carrie Reinhardt Adams, Enrique Latimer, Charles W. Martin, Christine Rohal, and Jodi Slater. https://edis.ifas.ufl.edu/ss685

Although rivers are of immense practical, aesthetic, and recreational value, these aquatic habitats are particularly sensitive to environmental changes. Increasingly, changes in streamflow and water quality are resulting in blooms of bottom-attached (benthic) algae, also known as periphyton, which have become widespread in many water bodies of US national parks. Because these blooms degrade visitor experiences and threaten human and ecosystem health, improved methods of characterizing benthic algae are needed. This study evaluated the potential utility of remote sensing techniques for mapping variations in algal density in shallow, clear-flowing rivers. As part of an initial proof-of-concept investigation, field measurements of water depth and percent cover of benthic algae were collected from two reaches of the Buffalo National River along with aerial photographs and multispectral satellite images. Applying a band ratio algorithm to these data yielded reliable depth estimates, although a shallow bias and moderate level of precision were observed. Spectral distinctions among algal percent cover values ranging from 0 to 100% were subtle and became only slightly more pronounced when the data were aggregated to four ordinal levels. A bagged trees machine learning model trained using the original spectral bands and image-derived depth estimates as predictor variables was used to produce classified maps of algal density. The spatial and temporal patterns depicted in these maps were reasonable but overall classification accuracies were modest, up to 64.6%, due to a lack of spectral detail. To further advance remote sensing of benthic algae and other periphyton, future studies could adopt hyperspectral approaches and more quantitative, continuous metrics such as biomass.

Despite being recognized as a key component of shallow-water ecosystems, submerged aquatic vegetation (SAV) remains difficult to monitor over large spatial scales. Because of SAV’s structuring capabilities, high-resolution monitoring of submerged landscapes could generate highly valuable ecological data. Until now, high-resolution remote sensing of SAV has been largely limited to applications within costly image analysis software. In this paper, we propose an example of an adaptable open-sourced object-based image analysis (OBIA) workflow to generate SAV cover maps in complex aquatic environments. Using the R software, QGIS and Orfeo Toolbox, we apply radiometric calibration, atmospheric correction, a de-striping correction, and a hierarchical iterative OBIA random forest classification to generate SAV cover maps based on raw DigitalGlobe multispectral imagery. The workflow is applied to images taken over two spatially complex fluvial lakes in Quebec, Canada, using Quickbird-02 and Worldview-03 satellites. Classification performance based on training sets reveals conservative SAV cover estimates with less than 10% error across all classes except for lower SAV growth forms in the most turbid waters. In light of these results, we conclude that it is possible to monitor SAV distribution using high-resolution remote sensing within an open-sourced environment with a flexible and functional workflow.

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The potential for rapid coastline modification in the face of sea‐level rise or other stressors is alarming, since coasts are often densely populated and support valuable infrastructure. In addition to coastal submergence, nutrient‐related water pollution is a growing concern for coastal wetlands. Previous studies found that the Suspended Sediment Concentration (SSC) of coastal wetlands acts as a first‐order control of their sustainability, but SSC dynamics are poorly understood. Our study focuses on the Virginia Coast Reserve (VCR) Long Term Ecological Research (LTER) site, a shallow multiple tidal inlet system in the USA. We apply numerical modelling (Delft3D‐SWAN) and subsequent analyses to determine SSC dynamics within the VCR. In particular, we consider two important controls on SSC in the system: vegetation (seagrass and salt marsh) and offshore waves. Our results show that vegetation colonies and increased wave energy lengthen water residence time. The reduction in the tidal prism decreases SSC export from the bay via tidal inlets, leading to increased sediment retention in the bay. We found that alongshore currents can enhance lagoon SSC by importing fine sediments from an adjacent inlet along the coastline. Our numerical experiments on vegetation seasonality can improve the understanding of wave climate impact on coastal bay sediment budget. Offshore waves increase sediment export from coastal bays, particularly during winter seasons with low vegetation density. Therefore, our study can help managers and stakeholders to understand how to implement restoration strategies for the VCR. © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Lake water levels can be managed in shallow lakes in order to improve water quality and promote aquatic vegetation that presumably benefits waterbirds. We aimed to understand whether waterbird abundance and species richness during fall migrations were positively influenced by managed lake water levels at 32 shallow lakes over 10 years. We conducted annual waterbird surveys that counted 6 million birds and repeatedly measured several in-lake habitat variables. Lakes with water level management had lower water depths, greater water quality and clarity, more submerged aquatic vegetation (SAV), and more wild rice (Zizania palustris L.) compared to unmanaged lakes. Redundancy analysis and regressions revealed that the waterbird community and several waterbird species were positively correlated to water level management and SAV; however, waterbirds were apparently responding principally to abundant SAV regardless of water depth or management. Two presented case studies of turbid-state lakes also highlighted that water level management rehabilitated lake habitat and waterbird use for a few years. We concluded that water level management can be an effective tool for increasing SAV and migrating waterbirds, but noted that large bird communities can also occur on unmanaged, deeper wetlands with existing SAV coverage of > 80%. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation (SAV) is considered an important driver of the zooplankton community, owing to the refuge offered by its structural complexity. However, non-destructive in situ approaches to assess quantitatively the features of SAV beds and their effects on zooplankton community are still lacking. This study aims to: 1) estimate SAV cover and complexity using subaquatic upward photographs (SUP) and 2) analyse the relationship between SAV variables and crustacean zooplankton composition and functional diversity (FD). SAV biomass and zooplankton were sampled at 52 stations in a large fluvial lake. Two metrics based on SUP were used to quantify SAV cover and complexity: 1) the percentage of the underwater landscape occupied by SAV (PLAND: SAV cover), and 2) its perimeter-area fractal dimension (PAFRAC: SAV complexity). Zooplankton composition and functional diversity were estimated based on crustacean species assemblages and functional traits. We used linear models to describe the relationships between SAV indices, environmental variables and zooplankton abundance, biomass and FD. SUP was an effective method to estimate in situ SAV cover and complexity. PLAND and PAFRAC were positively related to SAV biomass and zooplankton abundance, yielding a non-destructive assessment of the SAV-zooplankton relationships. Our study partially supports the habitat complexity-ecological niche availability hypothesis, as SAV cover and complexity influenced zooplankton functional groups and diversity indices. However, water transparency and depth also had important effects in interaction with PLAND and PAFRAC, and it remains difficult to fully disentangle the effects of SAV complexity from SAV cover on crustacean zooplankton community structure. [ABSTRACT FROM AUTHOR]

Subtidal habitats have not yet been accounted for in habitat maps of South African estuaries. In this study, a novel method for mapping subtidal estuarine habitats, using a remotely operated underwater vehicle (ROV) piloted from a boat, was developed and tested in the Knysna Estuary. Video footage was recorded along 48 transects across the width of the estuary, and then reviewed to identify, classify and map habitats. Using the method developed in this study, 21 hours of footage was recorded over 15 days of sampling, and about 30 hours of post-processing was carried out to map an area exceeding 850 ha. This study has produced the first baseline dataset of subtidal habitats for a South African estuary. Additionally, the study revealed the previously unknown distribution of the invasive red seaweed Asparagopsis taxiformis, and the underestimation in previous studies of the estuary of area cover of eelgrass Zostera capensis by 130 ha. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation (SAV) provides primary products for the food web, as well as shelter and nursery for many juvenile species. SAV can also attenuate waves, stabilize the seabed, and improve water quality. These environmental services are influenced by the dynamic motion of SAV. In this paper, a consistent‐mass cable model was developed to investigate flow interaction with a flexible vegetation blade. Compared with previous vegetation models, the cable model showed improvements in simulating blade motions in waves with and without currents, especially for "second‐normal‐mode‐like" blade motion. Wave asymmetry would cause blade motion to be asymmetric. However, asymmetric blade motion may also occur in symmetric waves. Results indicate that the asymmetric blade motion in symmetric waves is induced by two major mechanisms: (i) the spatial asymmetry of the encountered wave orbital velocities (wave motion relative to blade) due to blade displacements and (ii) the asymmetric action on the blade by vertical wave orbital velocities. Consequently, the blade motion is asymmetric even underneath symmetric waves unless (i) blade length (l) is much smaller than the wavelength (l/L≪1), (ii) blade length is much smaller than the water depth (l/h≪1) in finite water depth waves, or (iii) water depth is much smaller than the wavelength (h/L≪1). Peak asymmetric blade motion occurs as l/L increases to a critical value. The peak asymmetry increases with wave height and blade length but decreases with increasing blade flexural rigidity. Blade motion characteristics play an important role in wave‐vegetation interaction, wave‐driven currents, wave‐attenuation capacity, breakage of vegetation and ecosystem services. Plain Language Summary: Submerged aquatic vegetation (SAV) can reduce wave energy, stabilize the seabed, and improve water quality. These environmental services are influenced by SAV motion. In this paper, a numerical model was developed to study flow interaction with a flexible blade. Compared with previous vegetation models, the cable model showed improvements in simulating blade motions in waves with and without currents. Wave asymmetry would cause blade motion to be asymmetric. However, asymmetric blade motion may also occur in symmetric waves. Results indicate that the asymmetric motion in symmetric waves is induced by two major factors: (i) the spatial asymmetry of the encountered wave velocities (wave motion relative to blade) due to blade displacements and (ii) the asymmetric action on the blade by vertical wave velocities. Consequently, the blade motion is asymmetric unless (i) blade length is much smaller than the wavelength, (ii) blade length is much smaller than the water depth in non‐deep‐water waves, or (iii) water depth is much smaller than the wavelength. Peak asymmetric blade motion increases with wave height and blade length but decreases with increasing blade flexural rigidity. Blade motion characteristics play an important role in wave‐vegetation interaction, wave‐driven currents, wave‐attenuation capacity, breakage of vegetation and ecosystem services. Key Points: Simulations for the motion of flexible blades in waves with and without currents are improved by using a consistent‐mass cable modelBlade motion is asymmetric due to blade deflection and vertical wave velocity but symmetric if blade length is far less than the wavelengthPeak asymmetry of vegetation blade motion increases with wave height and blade length but decreases with increasing blade flexural rigidity [ABSTRACT FROM AUTHOR]

Carbon and nutrient storage are important ecosystem services of submerged aquatic vegetation (SAV) and may be enhanced by SAV restoration. This study demonstrates an approach to quantifying the nutrient and carbon storage potential of SAV restoration, focusing on the SAV Vallisneria americana in the oligohaline reaches of Florida's Caloosahatchee River Estuary (CRE). The variables of habitat area, plant size, plant density, and tissue nutrient stoichiometry are considered, and estimates are made both for storage in living tissue and for deposition in sediments. System-specific parameter values are obtained from a combination of abundance surveys, historical accounts of abundance and distribution, and field and mesocosm studies of tissue stoichiometry responses to nutrient addition. These are integrated with literature values for sediment deposition rates of C, N, and P in other SAV systems to estimate carbon and nutrient storage for current conditions and various restoration scenarios. Calculations indicate that under a restoration scenario assuming a return to the abundance documented in 1998–1999, V. americana tissues could act as a substantial sink for macro-elements in the CRE, representing 28.4 mt-C, 2.6 mt-N, and 0.16 mt-P, and depositing 897 mt-C y−1, 68.5 mt-N y−1, and 3.87 mt-P y−1 in meadow sediments. However, at current low shoot densities and small shoot sizes, these benefits are two to three orders of magnitude less. In addition to the large difference between the restoration and current-conditions scenarios, propagation of uncertainty around parameter estimates within each scenario leads to wide ranges of uncertainty around model outputs. More system-specific empirical studies would help constrain parameter estimates and improve the model. Overall, these findings emphasize the sensitivity of C, N, and P storage and deposition rates to SAV habitat conditions, and the importance of reversing declines in SAV density through restoration, and other conservation measures. • Procedures are developed to estimate nutrient and carbon storage benefits of submerged aquatic vegetation restoration. • Storage estimates for restored habitats are orders of magnitude higher than those for degraded habitats. • Plasticity in plant tissue nutrient stoichiometry could help submerged aquatic vegetation mitigate the impacts of excess nutrient loading. [ABSTRACT FROM AUTHOR]

The Everglades Stormwater Treatment Areas (STAs) are a 25,000 ha (61,000 acre) complex of constructed wetlands built to remove phosphorus (P) from agricultural and urban runoff in support of Everglades restoration. These STAs treat inflow waters that contain P in concentrations from 100 to 200 μg L−1, average calcium (Ca) concentrations of 60–90 mg L−1, and alkalinity (Alk) in the range of 150–350 mg L−1 as calcium carbonate (CaCO 3). Photosynthesis, primarily from submerged aquatic vegetation (SAV) within these STAs, increases water pH resulting in CaCO 3 formation, which is thought to contribute to P removal through coprecipitation and other processes. Since 2002, the STA complex has removed over 3000 MT of P and over 400,000 MT of Ca. Because the STAs at times treat Lake Okeechobee waters that are lower in Ca and Alk (35–50 mg L−1 and 95–125 mg L−1 as CaCO 3 , respectively), we conducted two experiments to explore the role of Ca and Alk on wetland P removal. First, in outdoor flow-through microcosms (0.18 m2) containing Najas guadalupensis and treating artificial inflow solutions, Ca/Alk at typical STA inflow concentrations (77 mg Ca L−1/316 mg L−1 as CaCO 3) resulted in significantly lower outflow P concentrations compared to lower Ca/Alk treatments (28 mg Ca L−1/67 mg L−1 as CaCO 3). Based on sediment organic carbon to total P (TP) ratios, organic matter production and sedimentation was the P removal mechanism under low Ca/Alk levels, where CaCO 3 precipitation did not occur, and also under high Ca/Alk, low P (31 μg L−1) conditions, despite CaCO 3 formation. High Ca/Alk increased organic matter sedimentation and associated P burial at low and high (168 μg L−1) water P concentrations. Additional P removal associated with CaCO 3 precipitation occurred only under high Ca/Alk, high P concentrations, and accounted for about 47% of P sedimentation in those microcosms. Second, in flow-through mesocosms (4.75 m2) containing STA muck soil and common STA SAV species, elevated Ca/Alk (94 mg Ca L−1/185 mg L−1 as CaCO 3) produced significantly lower outflow TP concentrations than treatments receiving unamended Lake Okeechobee inflow water with lower Ca/Alk concentrations (44 mg Ca L−1/112 mg L−1 as CaCO 3). In the same experiment, Ca/Alk levels had no effect on P removal in mesocosms containing Typha domingensis , a common STA emergent macrophyte species. SAV mesocosms produced lower outflow TP concentrations than Typha , regardless of Ca/Alk levels. In a follow-on laboratory incubation, low Ca/Alk concentrations in incubation waters did not increase P release from sediments formed under prior low or high inflow Ca/Alk concentrations in the SAV mesocosms, but anoxia sharply increased P release from both. These experiments suggest that coprecipitation with CaCO 3 is a meaningful P removal process in hardwater wetlands where high P concentrations and SAV coincide. Conversely, in STA outflow regions, where surface water P has already been treated to a low level, coprecipitation with CaCO 3 probably does not contribute to further P reductions. However, Ca/Alk also may contribute to inorganic-C availability which influences submerged aquatic productivity, so the role of inorganic C limitation on STA vegetation communities and P removal merits further study. • CaCO 3 precipitates in wetlands with SAV treating P for Everglades restoration. • Ca/Alk increased P removal in SAV systems via greater organic matter production. • Additional P coprecipitated with CaCO 3 only under high water P and Ca/Alk levels. • SAV outperformed Typha for P removal at both high and low Ca/Alk concentrations. • Low Ca/Alk inflow waters should not destabilize P in calcareous soils. [ABSTRACT FROM AUTHOR]

The biogeochemical response to different flow conditions within two parallel, well-performing flow-ways (FWs) in Everglades Stormwater Treatment Area (STA)-2 was studied. Three flow events in FW1, an emergent aquatic vegetation (EAV) based system and three flow events in FW3, a submerged aquatic vegetation (SAV) dominated system, were carried out between August 2015 and July 2017. These flow events included either low or moderate flow that was preceded and/or followed by no flow. These flow scenarios were designed to simulate different hydraulic and hydrologic conditions that STAs experience during full-scale operations. Hydraulic loading rates (HLRs, flow volume per day/wetland effective treatment area) during the flow events ranged from 0.5 to 10.4 cm d−1 with resulting phosphorus loading rates (PLRs, daily load/wetland effective treatment rate) of 1 to 20 mg P m−2 d−1. The ability of these flow-ways to remove and transform P in the water column under different flow conditions was evaluated using water quality data from autosamplers and weekly grab samples collected at six monitoring stations along each flow-way. Distinct water column concentration gradients of total phosphorus (TP) from inflow to outflow at all phases of the flow events for both flow-ways were observed. The magnitude at which P is removed from the water column increased with fractional distance from the inflow and was greater for the EAV-dominated system (FW1) than the SAV-based system (FW3). This system response translated to higher TP concentration reduction in EAV than SAV. Inflow to outflow TP concentration reductions for EAV were 94, 88, and 86% for moderate (MF), low (LF), and no flow (NF), respectively. For SAV, TP concentration reductions were 73, 71, and 64% for MF, LF, and NF, respectively. A significant increase in TP concentrations [largely dissolved organic P (DOP) and particulate P (PP)] in the SAV-dominated system was observed under no flow condition. The increase was attributed to in-situ production of PP through several mechanisms that likely include phytoplankton growth, periphyton sloughing, litter fragmentation, and resuspension via entrainment or bioturbation. While soluble reactive P (SRP) was the dominant form of inflow TP removed along the EAV FW, PP accounted for most of the reduction in TP concentration along the SAV FW, under both flow and no flow conditions. Particulate P and DOP comprised the residual P pool at the outflow region of each FW with slightly higher concentrations in the SAV than the EAV FW under no flow condition. The removal of P from the water column in the EAV FW was largely attributed to biotic processes (i.e., P uptake by biota) while coupled biotic and abiotic processes regulated P reduction in the SAV FW. • The biogeochemical P response to flow conditions differed between flow-ways. • TP concentration reductions were greater in the EAV relative to SAV and were highest under periods of flow compared to no flow for both flow-ways. • Outflow TP concentrations, which consisted largely of particulate and dissolved organic P, were highest under no flow and lowest under moderate flow. • The production of particulate P under no flow condition can influence how flows are managed in the STAs. [ABSTRACT FROM AUTHOR]

Vallisneria americana is a broadly distributed North American macrophyte with growth characteristics that vary across regions. While its reproductive traits may also differ with geography, most investigations have occurred in its northern extent, resulting in uncertainty regarding life history and germination strategies in sub-tropical populations. We conducted field monitoring and greenhouse and growth chamber experiments to investigate sub-tropical V. americana seed production, seed banking, and germination cues in central Florida, USA. We observed seed production nearly year-round, which produced a persistent seed bank (where present), with variable, but sometimes high densities (0–6209 seeds/m2). Unlike northern populations that germinate readily, these sub-tropical seeds were dormant, as germination was minimal across temperatures 20–30ºC in light or dark conditions. We found germination was not initiated by individual factors including temperature shifts, warm or cold stratification, high or low dissolved oxygen, or chemicals common in submerged sediments (ethylene or ethanol). However, germination did occur when organic material (sediments and/or vegetative extracts) was present combined with light or following scarification; and germination was enhanced by ethanol and cold-stratification. We also found that germination occurs in organic sediments exposed to high-oxygen conditions but is further improved in low-oxygen organic sediments, possibly mediated by the release of ethanol during oxygen reduction. This enhanced germination in light, decaying organic material, low-oxygen conditions, and ethanol suggests a germination strategy focused on exploiting openings in existing vegetation following disturbance. Without tubers that are present in northern ecotypes, sub-tropical V. americana may rely on seed germination for population maintenance. • Sub-tropical Vallisneria americana populations produce dormant seeds. • Sub-tropical populations reproduce nearly year-round and the seed bank is persistent. • Germination is initiated by contact with organic sediments or scarification. • Germination is enhanced by cold stratification and ethanol. [ABSTRACT FROM AUTHOR]

Submerged macrophytes are important primary producers for shallow lake systems. So far, their overall role in regulating lake methane flux is a subject of debate because the oxygen produced by their roots can promote methane oxidation in the sediment but they can also enhance methanogenesis through organic substrate production. In this study, we used the eddy covariance method to investigate the temporal dynamics of the CH 4 flux in a habitat of submerged macrophytes in Lake Taihu. The results show that the nighttime CH 4 flux is on average 33% higher than the daytime flux, although a clear diurnal pattern is evident only in the spring. At the daily to the seasonal time scale, the sediment temperature is the main driver of the CH 4 flux variations, implying higher methane production in the sediment at higher temperatures. The annual CH 4 emission (6.12 g C m−2 yr−1) is much higher than the published whole-lake mean flux (1.12 g C m−2 yr−1) and that reported previously in the eutrophic phytoplankton zone of the lake (1.35 g C m−2 yr−1), indicating that the net effect of the submerged macrophytes is to enhance methane emission. At the annual time scale, 3.5% of the carbon gained by the net ecosystem production is lost to the atmosphere in the form of CH 4. Unlabelled Image • The CH 4 flux is on average higher at night than during the day, although considerable scatter exists in the diurnal pattern. • Sediment temperature is a dominant driver that determines daily to seasonal variations of the CH 4 flux. • The CH 4 flux shows a low temperature sensitivity (Q 10 = 1.79) in the submerged aquatic vegetation zone of the lake. • Carbon loss via CH 4 emission is about 3.5% of the annual net ecosystem production. [ABSTRACT FROM AUTHOR]

Submerged aquatic vegetation (SAV) provides critical habitat for estuarine nekton in the Gulf of Mexico, but habitat quality of SAV beds may change when nonnative species, such as Eurasian watermilfoil (Myriophyllum spicatum), become established. We compared the habitat value of Myriophyllum with another common native SAV (Ruppia maritima) by using field collections to document shifts in nekton community structure and a field experiment to compare growth rates of commercially important juvenile white shrimp (Litopenaeus setiferus). Similar communities were collected from both SAV species, though nekton abundance scaled with SAV biomass. The habitat quality provided by Myriophyllum for white shrimp appeared to meet or exceed that of Ruppia, with densities and growth rates of shrimp in Myriophyllum (2.2 ± 0.47 m−2, 1.0 ± 0.07 mm TL day−1, 25.7 ± 2.98 mg day−1) higher than in Ruppia (1.0 ± 0.36 m−2, 0.6 ± 0.09 mm TL day−1, 11.6 ± 2.04 mg day−1). Though differences were detected between SAV species, other factors, such as hypoxia and interspecific competition, likely contributed to the differences we documented between these habitat types in shrimp densities and growth. Our study provides an example of a nonnative habitat-forming species providing a viable alternative to native habitat. This result contradicts the paradigm of negative effects associated with nonnative species following their introduction into an ecosystem. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • P removal in constructed wetlands can be limited by internal loading from soil. • Substrate management in downstream areas could help extend P removal limits. • Vegetated soil P release studies showed advantage of limerock substrate over muck. • Results are relevant to Everglades restoration, and wetland P cycling in general. Abstract Submerged aquatic vegetation (SAV) has been successfully used in wetland-based water treatment systems due to its capacity for rapid nutrient uptake, water-column oxygenation, and dampening of sediment resuspension. For Everglades restoration, large engineered wetlands known as Stormwater Treatment Areas (STAs) rely heavily on SAV-dominated treatment cells, since they have been highly efficient at reducing phosphorus (P) in surface waters to mesotrophic levels (12–25 µg/L). However, Everglades STAs have strict water quality effluent limits (∼13 µg/L), and many SAV cells are unable to regularly achieve such levels. In shallow aquatic systems, SAV can be a potential source of internal P loading from sediment to the water column via "nutrient pumping" through root uptake and leaf turnover. This mechanism may be an important obstacle to achieving lower wetland outflow P concentrations, but little is known of the interactions between substrate and SAV nutrition under these low-nutrient conditions. Soil core microcosms were incubated with or without macrophytes to estimate internal P loading potential in an SAV wetland and test the hypothesis that wetland substrate manipulation in the downstream (outflow) region might have reduced such loads and enabled more reliable delivery of low-P discharges. During six sequential two-week batch incubations, water-column P concentrations above muck soil overlain by accrued marl (typical of substrates in existing SAV-dominated STAs) indicated significantly higher internal P loading and higher macrophyte biomass growth than above either a bare limerock (LR) substrate (representative of a 40-ha pilot substrate manipulation study, where the muck soil was removed to expose the underlying limestone bedrock, i.e., "limerock") or LR with an accrued marl layer (representing post-startup conditions in the pilot, after muck removal and subsequent sediment accumulation under treatment wetland conditions). The results suggest that by removing muck soils to expose a LR substrate in the pilot wetland, SAV biomass and tissue P were diminished, thus reducing the potential for internal loading from SAV, which supports our hypothesis. For each of the three substrate types, internal P loading was higher in the presence of a vascular rooted plant, Potamogeton illinoensis , than the non-vascular macro-alga, Chara sp., (both taxa are prevalent in full-scale STAs), while internal loading was not different between Chara and the non-vegetated control. This indicates the role of P mining by rooted SAV. Overall, this study furthers our understanding of the wetland P cycle at near-oligotrophic levels, and is relevant to STA optimization for Everglades restoration. [ABSTRACT FROM AUTHOR]

Submerged Aquatic Vegetation (SAV) in coastal habitats plays critical roles because it protects coastlines, prevents erosion, provides nursery habitat, and dissolved oxygen. Meiobenthic communities in these habitats also play a key role in ecosystems processes. However, currently SAV loss continues unabated globally. Our understanding of the impact this loss has on meiobenthic communities is limited. To assess the impact of SAV cover on nematode communities, we studied nematode communities at Currituck Sound, NC, by comparing communities at an unvegetated and at an SAV site. Nematodes were identified to genus level morphologically. Our results showed that general diversity was low compared to other comparable sites with only 10 genera at both sites. Diversity and community structure were distinct at the two sites indicating that submerged aquatic vegetation may impact community structure of nematodes. [ABSTRACT FROM AUTHOR]

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Submerged aquatic vegetation (SAV) is a critical component of aquatic ecosystems. It is however understudied and rapidly changing due to global climate change and anthropogenic disturbances. Remote sensing (RS) can provide the efficient, accurate and large-scale monitoring needed for proper SAV management and has been shown to produce accurate results when properly implemented. Our objective is to introduce RS to researchers in the field of aquatic ecology. Applying RS to underwater ecosystems is complicated by the water column as water, and dissolved or suspended particulate matter, interacts with the same energy that is reflected or emitted by the target. This is addressed using theoretical or empiric models to remove the water column effect, though no model is appropriate for all aquatic conditions. The suitability of various sensors and platforms to aquatic research is discussed in relation to both SAV as the subject and to project aims and resources. An overview of the required corrections, processing and analysis methods for passive optical imagery is presented and discussed. Previous applications of remote sensing to identify and detect SAV are briefly presented and notable results and lessons are discussed. The success of previous work generally depended on the variability in, and suitability of, the available training data, the data’s spatial and spectral resolutions, the quality of the water column corrections and the level to which the SAV was being investigated (i.e., community versus species.)

The Everglades Stormwater Treatment Areas (STAs), a network of large, constructed wetlands, were built to reduce phosphorus (P) in water discharged into downstream oligotrophic Everglades ecosystem. These wetlands are colonized by two main types of macrophyte communities: emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV). The objective of this study was to compare the seasonal and spatial patterns of surface water quality within two flow-ways (FWs) in STA-2 (FW1 dominated by EAV and FW3 a mixed marsh with both EAV and SAV) and assess how surface water quality was affected by extreme storm events. Surface water samples were collected from three stations (near the inflow, middle of the FW, and near the outflow) along the flowpath of each FW four times from 2016 to 2018. Total P and its fractions generally decreased along the flowpath in both FWs while other elements did not show a consistent trend between seasons. Surface water quality in FW1 had more evident seasonal patterns and was less affected by 2017 storm events compared to that of FW3. The changes and patterns of water quality indicate that the processes (e.g., plant nutrient uptake, microbial assimilation, detritus decomposition and particle settling, etc.), which take the primary role of removing nutrients from the water column in FW1, vary not only due to the differences in plant growth but also to variations of hydraulic and nutrient loadings over wet and dry seasons. In FW3, on the contrary, our results indicate that the occlusion process facilitated by underwater photosynthesis of SAV likely enhanced the capacity of removing P and associated elements from water column and attenuated the seasonal differences. The SAV in FW3 also was susceptible to extreme events, with both short- and long-term adverse effects of storm events on surface water quality. • TP and its fractions decreased along the flow-path while other elements did not show a consistent trend between seasons. • EAV dominated system showed remarkable resilience to storm events and had evident seasonal patterns in surface water quality. • Occlusion process facilitated by SAV attenuated the seasonal differences of surface water, but SAV was susceptible to extreme events. [ABSTRACT FROM AUTHOR]

Microphytobenthos play a key role as food resources at the base of the trophic web, particularly in sediments of highly productive seagrass meadows. Here, we investigated patterns of variation in microphytobenthic diatom communities and their driving factors in an impacted versus non-impacted meadow of Ruppia maritima in the Patos lagoon estuary (Brazil), across seasons in two consecutive years. We found higher taxa richness, diversity and equitability, together with lower dominance, at the non-impacted meadow. Seasonally, the same pattern was found in autumn and/or winter 2017 at both meadows, driven by the lower seawater temperature. Higher richness was related to lower river discharge and equitability to lower wind velocity. Diatom assemblages differed in species presence/absence and abundance between meadows, mostly due to higher phosphate at the impacted meadow, together with higher water transparency and sediment organic matter (2016) and with higher grain size (2017) for species presence/absence. Even diatom assemblages differed more in terms of species abundances than of presence/absence, Paralia sulcata and Tryblionela compressa (commonly reported as indicator of eutrophic conditions) were exclusively present at the impacted meadow, while Amphora charrua, Desikaneis howellii, D. simplex (commonly in undisturbed environments) did so at the non-impacted meadow. Often two species were responsible for more than half the dissimilarities in abundances, with Catenula adhaerens dominating at the impacted meadow and Ambo tenuissimus at the non-impacted meadow. Overall, the combination of natural and anthropogenic environmental factors acted together to determine between-meadow and seasonal patterns of variation in the presence and abundance of diatom species. [Display omitted] • We examined environmental drivers of variation in sediment-associated diatom communities. • Sediment of Ruppia maritima meadows contains a highly diverse community. • Richness and diversity were often lower, and dominance higher, at the impacted meadow. • Higher phosphate at the impacted meadow explained most between-meadow variation. • Seasonal variation was influenced by several factors related to both water and sediment. [ABSTRACT FROM AUTHOR]