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Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Correlation (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon lagoon during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In this paper, spatial and temporal variations in vertical CO2 exchanges at the diurnal, tidal and seasonal scales are presented and discussed. In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the lagoon rapidly shifting from a sink to a source of CO2. CO2 fluxes showed generally low negative (influx) and positive (efflux) values and ranged from -- 13 to 19 µmol m-2 s-1 at maximum. Low tide and daytime conditions were always characterised by an uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22 ± 14% in the wind direction of measurements), CO2 influx was -1.7 ± 1.7 µmol m-2 s-1 at low tide during the day, and the efflux was 2.7 ± 3.7 µmol m-2 s-1 at low tide during the night. A gross primary production (GPP) of 4.4 µmol m-2 s-1 during emersion could be attributed mostly to microphytobenthic communities. During immersion, the water was a source of CO2 to the atmosphere, suggesting strong heterotrophy or resuspension of microphytobenthic cells. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92 ± 10 %), CO2 uptakes at low tide during the day were -1.5 ± 1.2 and -0.9 ± 1.7 µmol m-2 s-1, respectively. Night-time effluxes of CO2 were 1.0 ± 0.9 and 0.2 ± 1.1 µmol m-2 s-1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5 and 1.1 µmol m-2 s-1, respectively, attributed primarily to the seagrass community. At the same station in April 2009, before Zostera noltii started to grow, the CO2 uptake at low tide during the day was the highest (-2.7 ± 2.0 µmol m-2 s-1) and could be attributed to microphytobenthos dominance on NEP in this case. NEE versus PAR relationships for data ranked by wind directions were generally negative where and when Zostera noltii was dominant and positive when this community was minor. The latter relationship suggests important processes of photo-acclimatisation by the microphytobenthos, such as migration through the sediment. Influxes of CO2 were also observed during immersion at the central station in spring and early autumn and were apparently related to phytoplankton blooms occurring at the mouth of the lagoon, followed by the advection of CO2-depleted water with the tide. Although winter data would be necessary to determine a precise CO2 budget for the lagoon, our results suggest that tidal flat ecosystems are a modest contributor to the CO2 budget of the coastal ocean. [ABSTRACT FROM AUTHOR]

Measurements of carbon dioxide fluxes were performed over a temperate intertidal mudflat in southwestern France using the micrometeorological Eddy Covariance (EC) technique. EC measurements were carried out in two contrasting sites of the Arcachon flat during four periods and in three different seasons (autumn 2007, summer 2008, autumn 2008 and spring 2009). In addition, satellite images of the tidal flat at low tide were used to link the net ecosystem CO2 exchange (NEE) with the occupation of the mudflat by primary producers, particularly by Zostera noltii meadows. CO2 fluxes during the four deployments showed important spatial and temporal variations, with the flat rapidly shifting from sink to source with the tide. Absolute CO2 fluxes showed generally small negative (influx) and positive (efflux) values, with larger values up to -13 µmol m-2 s-1 for influxes and 19 µmol m-2 s-1 for effluxes. Low tide during the day was mostly associated with a net uptake of atmospheric CO2. In contrast, during immersion and during low tide at night, CO2 fluxes where positive, negative or close to zero, depending on the season and the site. During the autumn of 2007, at the innermost station with a patchy Zostera noltii bed (cover of 22±14% in the wind direction of measurements), CO2 influx was -1.7±1.7 µmol m-2 s-1 at low tide during the day, and the efflux was 2.7±3.7 µmol m-2 s-1 at low tide during the night. A gross primary production (GPP) of 4.4±4.1 µmol m-2 s-1 during emersion could be attributed to microphytobenthic communities. During the summer and autumn of 2008, at the central station with a dense eelgrass bed (92±10 %), CO2 uptakes at low tide during the day were -1.5±1.2 and -0.9±1.7 µmol m-2 s-1, respectively. Night time effluxes of CO2 were 1.0±0.9 and 0.2±1.1 µmol m-2 s-1 in summer and autumn, respectively, resulting in a GPP during emersion of 2.5±1.5 and 1.1±2.0 µmol m-2 s-1, respectively, attributed primarily to the seagrass community. At the same station in April 2009, before Zostera noltii started to grow, the CO2 uptake at low tide during the day was the highest (-2.7±2.0 µmol m-2 s-1). Influxes of CO2 were also observed during immersion at the central station in spring and early autumn and were apparently related to phytoplankton blooms occurring at the mouth of the flat, followed by the advection of CO2-depleted water with the flooding tide. Although winter data as well as water carbon measurements would be necessary to determine a precise CO2 budget for the flat, our results suggest that tidal flat ecosystems are a modest contributor to the CO2 budget of the coastal ocean. [ABSTRACT FROM AUTHOR]

Introduction: The blue mussel is one of the major aquaculture species worldwide. In France, this species faces a significant threat from infectious disease outbreaks in both mussel farms and the natural environment over the past decade. Diseases caused by various pathogens, particularly Vibrio spp., have posed a significant challenge to the mussel industry. Genetic improvement of disease resistance can be an effective approach to overcoming this issue. Methods: In this work, we tested genomic selection in the blue mussel (Mytilus edulis) to understand the genetic basis of resistance to one pathogenic strain of Vibrio splendidus (strain 14/053 2T1) and to predict the accuracy of selection using both pedigree and genomic information. Additionally, we performed a genome-wide association study (GWAS) to identify putative QTLs underlying disease resistance. We conducted an experimental infection involving 2,280 mussels sampled from 24 half-sib families containing each two full-sib families which were injected with V. splendidus. Dead and survivor mussels were all sampled, and among them, 348 dead and 348 surviving mussels were genotyped using a recently published multi-species medium-density 60K SNP array. Results: From potentially 23.5K SNPs for M. edulis present on the array, we identified 3,406 high-quality SNPs, out of which 2,204 SNPs were successfully mapped onto the recently published reference genome. Heritability for resistance to V. splendidus was moderate ranging from 0.22 to 0.31 for a pedigree-based model and from 0.28 to 0.36 for a genomic-based model. Discussion: GWAS revealed the polygenic architecture of the resistance trait in the blue mussel. The genomic selection models studied showed overall better performance than the pedigree-based model in terms of accuracy of breeding values prediction. This work provides insights into the genetic basis of resistance to V. splendidus and exemplifies the potential of genomic selection in family-based breeding programs in M. edulis. [ABSTRACT FROM AUTHOR]

The study provides significant insights into the community structure, species diversity and the environmental factors affecting the diversity of MPB in the tropical estuarine habitat of the Cochin estuary. A significant outcome of the present study was the taxonomic identification of 59 species of MPB belonging to 22 genera, which comprised 49 species of diatoms, one species of dinoflagellate, six species of cyanobacteria, two species of euglenophytes and one species of chlorophyte. Major MPB identified in the study were Navicula erifuga, Gyrosigma wansbeckii, Navicula flanatica, Nitzschia sigma, Nitzschia fluminensis, Amphora cymbifera, Nitzschia clausii, Nitzschia lorenziana, Navicula arenaria and Gyrosigma balticum. Principal component analysis indicated that the porewater salinity, sediment temperature, sediment pH, dissolved oxygen (DO), C:N ratio, porewater silicate and sediment chlorophyll a were positively correlated with the diversity of MPB. The intensity of rainfall, OC%, C:S ratio, and TN% were negatively correlated with the diversity of MPB. The study provides a detailed taxonomic inventory of MPB diversity and environmental influences, offering additional insights into tropical estuarine ecology. [ABSTRACT FROM AUTHOR]

Forest plantations cover a large percentage of global forest landscapes contributing significantly to carbon sequestration. By using continuous eddy covariance technique, we observed net ecosystem CO2 exchange (NEE), gross primary production (GPP), ecosystem respiration (ER), and meteorological variables from August 2018 to December 2019 in a Poplar plantation. The Poplar plantation ecosystem was a carbon sink overall, with high carbon uptake in growing season and limited uptake/emission in non-growing season. The annual cumulative NEE, GEP, and ER were −763.61, 1542.19, and 778.58 g C m−2 yr−1, respectively. Photosynthetically active radiation (PAR) significantly influenced NEE both at half-hourly and daily scale (P < 0.01 for both), while relative humidity (RH) and vapor pressure deficit (VPD) only significantly affected NEE at half-hourly scale (P < 0.01). The prevailing wind direction throughout 2019 was southeast and it varied between seasons. Southeast wind was the prevailing wind direction in summer and winter, while southwest and northeast wind were the dominant wind direction in spring and autumn, respectively. Our results highlight that polar plantations play an important role in storing carbon, and that understanding meteorological conditions is crucial in investigating ecosystem-atmosphere interactions and their impacts on carbon cycling. [ABSTRACT FROM AUTHOR]

Inland saline lakes play a key role in the global carbon cycle, acting as dynamic zones for atmospheric carbon exchange and storage. Given the global decline of saline lakes and the expected increase of periods of drought in a climate change scenario, changes in their potential capacity to uptake or emit atmospheric carbon are expected. Here, we conducted continuous measurements of CO2 and CH4 fluxes at the ecosystem scale in an endorheic saline lake of the Mediterranean region over nearly 2 years. Our focus was on determining net CO2 and CH4 exchanges with the atmosphere under both dry and flooded conditions, using the eddy covariance (EC) method. We coupled greenhouse gas flux measurements with water storage and analysed meteorological variables like air temperature and radiation, known to influence carbon fluxes in lakes. This extensive data integration enabled the projection of the net carbon flux over time, accounting for both dry and wet conditions on an interannual scale. We found that the system acts as a substantial carbon sink by absorbing atmospheric CO2 under wet conditions. In years with prolonged water storage, it is predicted that the lake's CO2 assimilation capacity can surpass 0.7 kg C m2 annually. Conversely, during extended drought years, a reduction in CO2 uptake capacity of more than 80 % is expected. Regarding CH4, we measured uptake rates that exceeded those of well-aerated soils such as forest soils or grasslands, reaching values of 0.2 µ mol m−2 s−1. Additionally, we observed that CH4 uptake during dry conditions was nearly double that of wet conditions. However, the absence of continuous data prevented us from correlating CH4 uptake processes with potential environmental predictors. Our study challenges the widespread notion that wetlands are universally greenhouse gas emitters, highlighting the significant role that endorheic saline lakes can play as a natural sink of atmospheric carbon. However, our work also underscores the vulnerability of these ecosystem services in the current climate change scenario, where drought episodes are expected to become more frequent and intense in the coming years. [ABSTRACT FROM AUTHOR]

The effects of climate change on coastal biodiversity are a major concern because altered community compositions may change associated rates of ecosystem functioning and services. Whilst responses of single species or taxa have been studied extensively, it remains challenging to estimate responses to climate change across different levels of biological organisation. Studies that consider the effects of moderate realistic near‐future levels of ocean warming and acidification are needed to identify and quantify the gradual responses of species to change. Also, studies including different levels of biological complexity may reveal opportunities for amelioration or facilitation under changing environmental conditions. To test experimentally for independent and combined effects of predicted near‐future warming and acidification on key benthic species, we manipulated three levels of temperature (winter ambient, +0.8 and +2°C) and two levels of pCO2 (ambient at 450 ppm and elevated at 645 ppm) and quantified their effects on mussels and algae growing separately and together (to also test for inter‐specific interactions). Warming increased mussel clearance and mortality rates simultaneously, which meant that total biomass peaked at +0.8°C. Surprisingly, however, no effects of elevated pCO2 were identified on mussels or algae. Moreover, when kept together, mussels and algae had mutually positive effects on each other's performance (i.e. mussel survival and condition index, mussel and algal biomass and proxies for algal productivity including relative maximum electron transport rate [rETRmax], saturating light intensity [Ik] and maximum quantum yield [Fv/Fm]), independent of warming and acidification. Our results show that even moderate warming affected the functioning of key benthic species, and we identified a level of resistance to predicted ocean acidification. Importantly, we show that the presence of a second functional group enhanced the functioning of both groups (mussels and algae), independent of changing environmental conditions, which highlights the ecological and potential economic benefits of conserving biodiversity in marine ecosystems. [ABSTRACT FROM AUTHOR]

Soil infiltration and evaporation are the main factors affecting the water cycle in arid and semi-arid areas, and the sealing measures determine the soil water storage capacity by affecting the evaporation and infiltration process of grassland soil water, which is the key to the ecological environment restoration of arid and semi-arid grassland. This study taking the enclosure time of Hulunbuir grassland for 3 years, 7 years, 10 years and the grazing control grassland as the research objects by using small evaporation instrument and double-ring infiltration instrument.To study the effects of enclosure measures on soil water distribution, soil infiltration and evaporation, and to evaluate the applicability of the main soil evaporation and infiltration models in enclosed grassland. The results show that (1) the enclosure measures can effectively improve the soil water content. In the vertical direction, the soil water content shows a trend of increasing first and then decreasing. (2) The initial infiltration rate and stable infiltration rate of grassland at different enclosure time are significantly different (P<0.05), and the soil infiltration rate and evaporation rate were in the order of EN10 >EN7 >EN3 >CK. (3) Using three infiltration process models to simulate the grassland infiltration process at different enclosure times, the Horton model is able to better model the inflection points of the infiltration process, and the fit accuracy is higher than that of the Philip and Kostiakov models. (4) The cumulative evaporation process of grassland at different closure times was simulated by using Black, Ross, and Power function models.The simulation values calculated by the Rose model are the closest to the measured value, and the simulation accuracy is the highest.The comprehensive analysis shows that the hydrological characteristics of grassland soil change significantly in the early stage of enclosure phase, and the soil properties have reached a good state for 3 to 7 years.With the continuous increase of enclosure time, the change of soil hydrological characteristics is not obvious. The results are helpful for soil and water conservation and ecological environment management in arid and semiarid grassland. [ABSTRACT FROM AUTHOR]

This study evaluated carbon dynamics in a carbonate microbasin (Bule stream), located in an important metallogenetic area (QF) in Brazil. River water collections were performed on a base and high flow. The microbasin showed high DIC, with HCO 3 - being the main component, followed by CO 2 . The pCO 2 showed high values, indicating fluxes in the water → air direction. The degassing was 683.4 mmol m -2  day -1 (average at low flow) and 43.4 mmol m -2  day -1 (average at high flow). The fluvial flow was 9 to 31 kg km -2  day -1 of HCO 3 - and 1.4 to 0.7 kg km -2  day -1 of CO 2 , respectively, at the base and high flow. Considering the importance of the lithological unit of the Minas Supergroup for the QF, the total flow of CO 2 released by all the basins that compose such units was estimated. The estimated values were 1.3 × 10 12  mmol day -1 in low flow and 8.4 × 10 10  mmol day -1 in high flow. The data obtained in this study were the first in the QF region. The Bule stream is an environmental protection area, free from contamination, considered a background for other drainage basins inserted in the QF. The results obtained reinforce the importance of hydrographic microbasins influence on the river carbon fluxes in a regional and global context., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Seagrasses are globally acknowledged as crucial habitats as they provide a variety of ecosystem services. Mexico's legislation protects most of these marine plants; however, the protection often fails in application. The Gulf of California, despite being a biodiversity hotspot, has scant data on seagrasses. Here, human activity and climate change increasingly threaten these coastal ecosystems, with conservation and research efforts lacking coordination at a regional level. Our manuscript aimed to review and standardize existing data on Gulf of California seagrass species, ensuring open access for data updates; pinpointing conservation deficiencies; and guiding future research. We have added new records to the official public data, but we were able to recapture only 25% of the seagrass locations meaning a potential reduction in their historical distribution of 45.8%. Even though Mexico's legislation protects some species of seagrasses, it protection often fails in the application. We identified that only 6.1% of the seagrass locations are within protected areas that recognize their presence in their management plans (e.g., the Balandra Flora and Fauna Protected Area and the Upper Gulf of California and Colorado River Delta Biosphere Reserve). At least 55.9% of seagrass records are associated with potentially damaging activities like pollution, coastal modification or biological resources use, while 23% are exposed to higher frequency of marine heatwaves. Given the importance of seagrass meadows under Mexican law and their internationally recognized ecological value, sharing current information and guiding research is essential. Our study seeks to galvanize renewed research initiatives and raise more awareness on the conservation of the Gulf of California's seagrasses. [ABSTRACT FROM AUTHOR]

Estuaries play an important role in connecting the global carbon cycle across the land-to-ocean continuum, but little is known about Australia's contribution to global CO2 emissions. Here we present an Australia-wide assessment, based on CO2 concentrations for 47 estuaries upscaled to 971 assessed Australian estuaries. We estimate total mean (±SE) estuary CO2 emissions of 8.67 ± 0.54 Tg CO2-C yr−1, with tidal systems, lagoons, and small deltas contributing 94.4%, 3.1%, and 2.5%, respectively. Although higher disturbance increased water-air CO2 fluxes, its effect on total Australian estuarine CO2 emissions was small due to the large surface areas of low and moderately disturbed tidal systems. Mean water-air CO2 fluxes from Australian small deltas and tidal systems were higher than from global estuaries because of the dominance of macrotidal subtropical and tropical systems in Australia, which have higher emissions due to lateral inputs. We suggest that global estuarine CO2 emissions should be upscaled based on geomorphology, but should also consider land-use disturbance, and climate. Australian estuaries shown to emit more CO2 per unit area than global estuaries due to the dominance of macrotidal subtropical and tropical tidal systems, while disturbance effects were minimal due to low overall disturbance. [ABSTRACT FROM AUTHOR]

Since the beginning of the industrial revolution, atmospheric carbon dioxide (CO 2) concentrations have risen steadily and have induced a decrease of the averaged surface ocean pH by 0.1 units, corresponding to an increase in ocean acidity of about 30 %. In addition to ocean warming, ocean acidification poses a tremendous challenge to some marine organisms, especially calcifiers. The need for long-term oceanic observations of pH and temperature is a key element to assess the vulnerability of marine communities and ecosystems to these pressures. Nearshore productive environments, where a large majority of shellfish farming activities are conducted, are known to present pH levels as well as amplitudes of daily and seasonal variations that are much larger than those observed in the open ocean. Yet, to date, there are very few coastal observation sites where these parameters are measured simultaneously and at high frequency. To bridge this gap, an observation network was initiated in 2021 in the framework of the CocoriCO 2 project. Six sites were selected along the French Atlantic and Mediterranean coastlines based on their importance in terms of shellfish production and the presence of high- and low-frequency monitoring activities. At each site, autonomous pH sensors were deployed, both inside and outside shellfish production areas, next to high-frequency CTD (conductivity–temperature–depth) probes operated through two operating monitoring networks. pH sensors were set to an acquisition rate of 15 min, and discrete seawater samples were collected biweekly in order to control the quality of pH data (laboratory spectrophotometric measurements) as well as to measure total alkalinity and dissolved inorganic carbon concentrations for full characterization of the carbonate system. While this network has been up and running for more than 2 years, the acquired dataset has already revealed important differences in terms of pH variations between monitored sites related to the influence of diverse processes (freshwater inputs, tides, temperature, biological processes). Data are available at 10.17882/96982 (Petton et al., 2023a). [ABSTRACT FROM AUTHOR]

Due to large losses of seagrass meadows worldwide, restoration is proposed as a key strategy for increasing coastal resilience and recovery. The emergence of a seagrass meadow is expected to substantially amplify biodiversity and enhance benthic metabolism by increasing primary productivity and respiration. Nevertheless, open questions remain regarding the metabolic balance of aging seagrass meadows and the roles benthic communities within the seagrass ecosystem play in overall metabolism. To address these questions, we investigated a chronosequence of bare sediments and adjacent Zostera marina meadows of 3 and 7 years since restoration alongside a natural meadow located within a high-temperate marine embayment in Gåsö, Sweden. We combined continuous measurements of O2 fluxes using underwater eddy covariance with dissolved inorganic carbon (DIC) and O2 fluxes from benthic chambers during the productive season (July). Based on the ratio between O2 and DIC, we derived site-specific photosynthetic and respiratory quotients, enabling the conversion of eddy covariance fluxes to DIC. We assessed benthic diversity parameters as potential drivers of metabolic flux variability. We observed high rates of gross primary productivity (GPP) spanning - 18 to - 82 mmolDICm-2d-1 , which increased progressively with meadow age. Community respiration (CR) mirrored the GPP trend, and all meadows were net heterotrophic (GPP < CR), with net community productivity (NCP) ranging from 16 to 28 mmolDICm-2d-1. While autotrophic biomass did not increase with meadow age, macrophyte diversity did, elucidating potential effects of niche complementarity among macrophytes on community metabolism. These findings provide valuable insights into how community composition and meadow development relate to ecosystem functioning, highlighting potential tradeoffs between carbon uptake and biodiversity. [ABSTRACT FROM AUTHOR]

Endocrine-disrupting chemicals (EDCs) represent a global threat to human health and the environment. In vertebrates, lipophilic EDCs primarily act by mimicking endogenous hormones, thus interfering with the transcriptional activity of nuclear receptors (NRs). The demonstration of the direct translation of these mechanisms into perturbation of NR-mediated physiological functions in invertebrates, however, has rarely proven successful, as the modes of action of EDCs in vertebrates and invertebrates seem to be distinct. In the present work, we investigated the members of the NR superfamily in a bivalve mollusk, the Mediterranean mussel Mytilus galloprovincialis. In addition to annotating the M. galloprovincialis NR complement, we assessed the potential developmental functions and susceptibility to EDC challenge during early development by gene expression analyses. Our results indicate that a majority of mussel NRs are dynamically expressed during early development, including receptors characterized by a potential susceptibility to EDCs. This study thus indicates that NRs are major regulators of early mussel development and that NR-mediated endocrine disruption in the mussel could be occurring at a larger scale and at earlier stages of the life cycle than previously anticipated. Altogether, these findings will have significant repercussions for our understanding of the stability of natural mussel populations. This article is part of the theme issue 'Endocrine responses to environmental variation: conceptual approaches and recent developments'. [ABSTRACT FROM AUTHOR]

Understanding the factors that control carbonate systems is an important goal due to the complex interactions between the hydrophysical and chemical–biological conditions in coastal basins. The results of this paper present the state of the carbonate system in Penzhina Bay and its adjacent waters—the Shelikhov Gulf—in July 2023, during spring tides with 13 m height. The area we studied included the length of the largest river in the region, the Penzhina River, from the peak of its summer flood to its boundary with the Shelikhov Gulf (the Sea of Okhotsk). This unique dynamic basin, with a length of about 800 km, was studied over 17 days. During this period, the entire water column of Penzhina Bay, down to a depth of about 60 m, and the surface water layer of the Shelikhov Gulf were undersaturated in terms of CO2, with low levels relative to those of the atmosphere. To explain this observation, the dissolved oxygen, nutrients in mineral and organic forms, humic substances, chlorophyll a, and photic zone thickness are presented for the entire basin under study, together with its hydrological data. The results of daily observations of the carbonate system at fixed anchorage stations characterize two contrasting regions of Penzhina Bay: one that was more exposed to continental runoff, which had salinity levels in the range of 8.0–21.3 psu during one tidal cycle; the second had smaller variations in salinity in the range of 31.6–32.9 psu during one tidal cycle. This study emphasizes the importance of biological processes and continental runoff on the variability of the carbonate system parameters and CO2 fluxes at a water/atmosphere boundary with extreme tidal conditions in this ecosystem that is barely affected by human activities. [ABSTRACT FROM AUTHOR]

Within the coastal zone, salt marshes are atmospheric CO2 sinks and represent an essential component of biological carbon (C) stored on earth due to a strong primary production. Significant amounts of C are processed within these tidal systems which requires a better understanding of the temporal CO2 flux dynamics, the metabolic processes involved and the controlling factors. Within a temperate salt marsh (French Atlantic coast), continuous CO2 fluxes measurements were performed by the atmospheric eddy covariance technique to assess the net ecosystem exchange (NEE) at diurnal, tidal and seasonal scales as well as the associated relevant biophysical drivers. To study marsh metabolic processes, measured NEE was partitioned into gross primary production (GPP) and ecosystem respiration (Reco) during marsh emersion allowing to estimate NEE at the marsh–atmosphere interface (NEEmarsh = GPP - Reco). During the year 2020, the net C balance from measured NEE was - 483 g C m -2 yr -1 while GPP and Reco absorbed and emitted 1019 and 533 g C m -2 yr -1 , respectively. The highest CO2 uptake was recorded in spring during the growing season for halophyte plants in relationships with favourable environmental conditions for photosynthesis, whereas in summer, higher temperatures and lower humidity rates increased ecosystem respiration. At the diurnal scale, the salt marsh was a CO2 sink during daytime, mainly driven by light, and a CO2 source during night-time, mainly driven by temperature, irrespective of emersion or immersion periods. However, daytime immersion strongly affected NEE fluxes by reducing marsh CO2 uptake up to 90 %. During night-time immersion, marsh CO2 emissions could be completely suppressed, even causing a change in metabolic status from source to sink under certain situations, especially in winter when Reco rates were lowest. At the annual scale, tidal immersion did not significantly affect the net C uptake of the studied salt marsh since similar annual balances of measured NEE (with tidal immersion) and estimated NEEmarsh (without tidal immersion) were recorded. [ABSTRACT FROM AUTHOR]

Eutrophication and hypoxia represent an ever-growing stressor to estuaries and coastal ecosystems due to population growth and climate change. Understanding water quality dynamics in shallow water systems is particularly challenging due to the complex physical and biogeochemical dynamics and interactions among them. Within shallow waters, benthic microalgae can significantly contribute to autotrophic primary production, generate organic matter, increase dissolved oxygen consumption, and alter nutrient fluxes at the sediment-water interface, yet they have received little attention in modeling applications. A state-of-the-art modeling system, the Semi-Implicit Cross-Scale Hydroscience Integrated System Model (SCHISM), coupled with the Integrated Compartment Model (ICM) of water quality and benthic microalgae, has been implemented in the Corsica River estuary, a tributary to Chesapeake Bay, to study benthic microalgal impact on water quality in shallow water systems. The model simulation has revealed a broad impact of benthic microalgae, ranging from sediment-water interface fluxes to water column dynamics, and the effects are observed from near-field to far-field monitoring stations. High-frequency variability and non-linearity dominate benthic microalgal dynamics, sediment oxygen demand, and nutrient fluxes at the sediment-water interface. Resource competition and supply determine the spatial scope of benthic microalgal impacts on far-field stations and the whole estuary system. Our study shows that benthic microalgae are a significant factor in shallow water dynamics that needs adequate attention in future observation and modeling applications. [ABSTRACT FROM AUTHOR]

Floodplain lakes are widespread and ecologically important throughout tropical river systems, however data are rare that describe how temporal variations in hydrological, meteorological and optical conditions moderate stratification and mixing in these shallow lakes. Using time series measurements of meteorology and water‐column temperatures from 17 several day campaigns spanning two hydrological years in a representative Amazon floodplain lake, we calculated surface energy fluxes and thermal stratification, and applied and evaluated a 3‐dimensional hydrodynamic model. The model successfully simulated diel cycles in thermal structure characterized by buoyancy frequency, depth of the actively mixing layer, and other terms associated with the surface energy budget. Diurnal heating with strong stratification and nocturnal mixing were common; despite considerable heat loss at night, the strong stratification during the day meant that mixing only infrequently extended to the bottom at night. Simulations indicated that the diurnal thermocline up and downwelled creating lake‐wide differences in near‐surface temperatures and mixing depths. Infrequent full mixing creates conditions conducive to anoxia in these shallow lakes given their warm temperatures. Key Points: Diel thermal structure in a tropical floodplain lake was characterized by high‐resolution field measurements over two hydrological yearsState and process evaluation show that diel and seasonal stratification and mixing were simulated well by a 3‐D hydrodynamic modelDiurnal heating with strong stratification and nocturnal mixing were common while mixing to the bottom was intermittent [ABSTRACT FROM AUTHOR]

Rivers and streams play an important role within the global carbon cycle, in part through emissions of carbon dioxide (CO2) to the atmosphere. However, the sources of this CO2 and their spatiotemporal variability are difficult to constrain. Recent work has highlighted the role of carbonate buffering reactions that may serve as a source of CO2 in high alkalinity systems. In this study, we seek to develop a quantitative framework for the role of carbonate buffering in the fluxes and spatiotemporal patterns of CO2 and the stable and radio‐ isotope composition of dissolved inorganic carbon (DIC). We incorporate DIC speciation calculations of carbon isotopologues into a stream network CO2 model and perform a series of simulations, ranging from the degassing of a groundwater seep to a hydrologically‐coupled 5th‐order stream network. We find that carbonate buffering reactions contribute >60% of emissions in high‐alkalinity, moderate groundwater‐CO2 environments. However, atmosphere equilibration timescales of CO2 are minimally affected, which contradicts hypotheses that carbonate buffering maintains high CO2 across Strahler orders in high alkalinity systems. In contrast, alkalinity dramatically increases isotope equilibration timescales, which acts to decouple CO2 and DIC variations from the isotopic composition even under low alkalinity. This significantly complicates a common method for carbon source identification. Based on similar impacts on atmospheric equilibration for stable and radio‐ carbon isotopologues, we develop a quantitative method for partitioning groundwater and stream corridor carbon sources in carbonate‐dominated watersheds. Together, these results provide a framework to guide fieldwork and interpretations of stream network CO2 patterns across variable alkalinities. Plain Language Summary: Streams emit a lot of carbon dioxide (CO2) to the atmosphere, but it is difficult to figure out where the CO2 originates. One source is a chemical reaction called carbonate buffering, which happens between different forms of dissolved inorganic carbon. This reaction may be important in streams with high alkalinity, but we lack knowledge about how it contributes across different alkalinities and scales. Some studies use isotopes of carbon to trace where CO2 comes from and how it is released, but we lack knowledge about how carbonate buffering affects isotope patterns. Here, we create mathematical models of CO2 production and release, including isotopes in streams. Our findings show that carbonate buffering can be a significant source of CO2 in streams with high alkalinity. However, it doesn't keep CO2 levels consistently high downstream, as studies previously suggested. Conversely, carbonate buffering has a big effect on the patterns of carbon isotopes. This means that common isotope methods for identifying stream CO2 sources don't work well. Instead, we propose how to use stable and radioactive carbon isotopes together to determine the sources of carbon. Our study aims to guide future work and help understand how carbonate buffering impacts CO2 patterns across stream environments. Key Points: We develop models of stream CO2 degassing that include carbonate buffering and apply them across a range of alkalinities and stream processesCarbonate buffering can support significant contributions to stream CO2 fluxes but cannot support elevated downstream CO2 concentrationsStable and radio‐ carbon isotopes are decoupled from CO2 by carbonate buffering but can be leveraged to partition carbon sources [ABSTRACT FROM AUTHOR]

To limit global warming below 2°C by 2100, we must drastically reduce greenhouse gas emissions and additionally remove ~100–900 Gt CO2 from the atmosphere (carbon dioxide removal, CDR) to compensate for unavoidable emissions. Seaweeds (marine macroalgae) naturally grow in coastal regions worldwide where they are crucial for primary production and carbon cycling. They are being considered as a biological method for CDR and for use in carbon trading schemes as offsets. To use seaweeds in carbon trading schemes requires verification that seaweed photosynthesis that fixes CO2 into organic carbon results in CDR, along with the safe and secure storage of the carbon removed from the atmosphere for more than 100 years (sequestration). There is much ongoing research into the magnitude of seaweed carbon storage pools (e.g., as living biomass and as particulate and dissolved organic carbon in sediments and the deep ocean), but these pools do not equate to CDR unless the amount of CO2 removed from the atmosphere as a result of seaweed primary production can be quantified and verified. The draw‐down of atmospheric CO2 into seawater is via air‐sea CO2 equilibrium, which operates on time scales of weeks to years depending upon the ecosystem considered. Here, we explain why quantifying air‐sea CO2 equilibrium and linking this process to seaweed carbon storage pools is the critical step needed to verify CDR by discrete seaweed beds and nearshore and open ocean aquaculture systems prior to their use in carbon trading. [ABSTRACT FROM AUTHOR]

Due to their role as primary producers, phytoplankton are essential to the productivity of estuarine ecosystems. However, it is important to understand how these nearly passive organisms are able to persist within estuaries when river inflow results in a net outflow to the ocean. Estuaries also represent challenging habitats due to a strong salinity gradient. Little is known about how phytoplankton are able to be retained within estuaries. We present a new individual-based Lagrangian model of the Elbe estuary which examines possible retention mechanisms for phytoplankton. Specifically, we investigated how reproduction, sinking and rising, and diel vertical migration may allow populations to persist within the estuary. We find that vertical migration, especially rising, favors retention, while fast sinking does not. We further provide first estimates of outwashing losses. Our simulations illustrate that riverbanks and tidal flats are essential for the long-term survival of phytoplankton populations, as they provide refuges from strong downstream currents. These results contribute to the understanding needed to advance the ecosystem-based management of estuaries. [ABSTRACT FROM AUTHOR]

Wetlands cover a small portion of the world, but have disproportionate influence on global carbon (C) sequestration, carbon dioxide and methane emissions, and aquatic C fluxes. However, the underlying biogeochemical processes that affect wetland C pools and fluxes are complex and dynamic, making measurements of wetland C challenging. Over decades of research, many observational, experimental, and analytical approaches have been developed to understand and quantify pools and fluxes of wetland C. Sampling approaches range in their representation of wetland C from short to long timeframes and local to landscape spatial scales. This review summarizes common and cutting-edge methodological approaches for quantifying wetland C pools and fluxes. We first define each of the major C pools and fluxes and provide rationale for their importance to wetland C dynamics. For each approach, we clarify what component of wetland C is measured and its spatial and temporal representativeness and constraints. We describe practical considerations for each approach, such as where and when an approach is typically used, who can conduct the measurements (expertise, training requirements), and how approaches are conducted, including considerations on equipment complexity and costs. Finally, we review key covariates and ancillary measurements that enhance the interpretation of findings and facilitate model development. The protocols that we describe to measure soil, water, vegetation, and gases are also relevant for related disciplines such as ecology. Improved quality and consistency of data collection and reporting across studies will help reduce global uncertainties and develop management strategies to use wetlands as nature-based climate solutions. [ABSTRACT FROM AUTHOR]

Intertidal microphytobenthic (MPB) biofilms are key sites for coastal primary production, predominantly by pennate diatoms exhibiting photo‐regulation via non‐photochemical quenching (NPQ) and vertical migration. Movement is the main photo‐regulation mechanism of motile (epipelic) diatoms and because they can move from light, they show low‐light acclimation features such as low NPQ levels, as compared to non‐motile (epipsammic) forms. However, most comparisons of MPB species‐specific photo‐regulation have used low light acclimated monocultures, not mimicking environmental conditions. Here we used variable chlorophyll fluorescence imaging, fluorescent labelling in sediment cores and scanning electron microscopy to compare the movement and NPQ responses to light of four epipelic diatom species from a natural MPB biofilm. The diatoms exhibited different species‐specific photo‐regulation features and a large NPQ range, exceeding that reported for epipsammic diatoms. This could allow epipelic species to coexist in compacted light niches of MPB communities. We show that diatom cell orientation within MPB can be modulated by light, where diatoms oriented themselves more perpendicular to the sediment surface under high light vs. more parallel under low light, demonstrating behavioural, photo‐regulatory response by varying their light absorption cross‐section. This highlights the importance of considering species‐specific responses and understanding cell orientation and photo‐behaviour in MPB research. [ABSTRACT FROM AUTHOR]

BlueCAM is an Australian coastal wetland restoration methodology for estimating atmospheric warming abatement. However, BlueCAM is incomplete and contains conceptual and formulation errors. Conceptually, sequestration may be understated by not accounting for an increase in animal biomass and baseline ecosystems as heterotrophic carbon sources. Or, more likely, sequestration services are significantly overestimated by not considering: (1) remineralization of allochthonous carbon, supplied from surrounding ecosystems; (2) the subtraction of a notable intrinsically recalcitrant allochthonous carbon fraction; (3) whether baseline ecosystems are autotrophic carbon sinks; and (4) the reduction in air–sea flux during periods of submersion. Erroneously, BlueCAM: (1) implies that any remains of labile allochthonous carbon should be subtracted from stocks, not just the recalcitrant fraction; and (2) does not embed additional warming from CH4 emissions within components of net ecosystem production. Taken together, these errors are likely to greatly overestimate both wetland sequestration and warming abatement services. [ABSTRACT FROM AUTHOR]

Permafrost degradation is altering biogeochemical processes throughout the Arctic. Thaw‐induced changes in organic matter transformations and mineral weathering reactions are impacting fluxes of inorganic carbon (IC) and alkalinity (ALK) in Arctic rivers. However, the net impact of these changing fluxes on the concentration of carbon dioxide in the atmosphere (pCO2) is relatively unconstrained. Resolving this uncertainty is important as thaw‐driven changes in the fluxes of IC and ALK could produce feedbacks in the global carbon cycle. Enhanced production of sulfuric acid through sulfide oxidation is particularly poorly quantified despite its potential to remove ALK from the ocean‐atmosphere system and increase pCO2, producing a positive feedback leading to more warming and permafrost degradation. In this work, we quantified weathering in the Koyukuk River, a major tributary of the Yukon River draining discontinuous permafrost in central Alaska, based on water and sediment samples collected near the village of Huslia in summer 2018. Using measurements of major ion abundances and sulfate (SO42− ${{\text{SO}}_{4}}^{2-}$) sulfur (34S/32S) and oxygen (18O/16O) isotope ratios, we employed the MEANDIR inversion model to quantify the relative importance of a suite of weathering processes and their net impact on pCO2. Calculations found that approximately 80% of SO42− ${{\text{SO}}_{4}}^{2-}$ in mainstem samples derived from sulfide oxidation with the remainder from evaporite dissolution. Moreover, 34S/32S ratios, 13C/12C ratios of dissolved IC, and sulfur X‐ray absorption spectra of mainstem, secondary channel, and floodplain pore fluid and sediment samples revealed modest degrees of microbial sulfate reduction within the floodplain. Weathering fluxes of ALK and IC result in lower values of pCO2 over timescales shorter than carbonate compensation (∼104 yr) and, for mainstem samples, higher values of pCO2 over timescales longer than carbonate compensation but shorter than the residence time of marine SO42− ${{\text{SO}}_{4}}^{2-}$ (∼107 yr). Furthermore, the absolute concentrations of SO42− ${{\text{SO}}_{4}}^{2-}$ and Mg2+ in the Koyukuk River, as well as the ratios of SO42− ${{\text{SO}}_{4}}^{2-}$ and Mg2+ to other dissolved weathering products, have increased over the past 50 years. Through analogy to similar trends in the Yukon River, we interpret these changes as reflecting enhanced sulfide oxidation due to ongoing exposure of previously frozen sediment and changes in the contributions of shallow and deep flow paths to the active channel. Overall, these findings confirm that sulfide oxidation is a substantial outcome of permafrost degradation and that the sulfur cycle responds to permafrost thaw with a timescale‐dependent feedback on warming. Key Points: Sulfide oxidation sources approximately 80% of dissolved SO42− ${{\text{SO}}_{4}}^{2-}$ in the Koyukuk River, Alaska, and may act as a positive feedback on modern warmingInversion calculations reveal weathering is a CO2 sink on timescales of ∼5–10 kyr and a CO2 source on timescales of ∼10 kyr to ∼10 MyrIncreases in the absolute and relative abundance of SO42− ${{\text{SO}}_{4}}^{2-}$ in the Koyukuk River and Yukon River over the past decades suggests thaw‐induced sulfide oxidation [ABSTRACT FROM AUTHOR]

Ionic strength (I; mol·L−1) acts as one of the most important parameters of natural waters. It is indispensable for obtaining ion activities and thus is crucial for describing chemical processes in water solutions. Limnology, I, has many applications, but calculating the partial pressure of CO2 (pCO2) and the carbonate saturation index (SI) are among the most important examples. The determination of I requires the full ion composition of water to be recognized, and when the concentration of some major ion(s) is/are missing altogether, the I value remains unknown. Because historical and monitoring data are often incomplete, it seems useful to provide a method for the indirect assessment of I. In this paper, we developed and tested an empirical model to estimate I on the basis of electric conductivity at 25 °C (EC). Our model consists of two linear equations: (i) Imod = 15.231 × 10−6·EC − 79.191 × 10−6 and (ii) Imod = 10.647 × 10−6·EC + 26.373 × 10−4 for EC < 592.6 μS·cm−1 and for EC > 592.6 μS·cm−1, respectively. We showed that model performance was better than the hitherto used EC–I relationships. We also demonstrated that the model provided an effective tool for limnological monitoring with special emphasis on the assessment of CO2 emissions from lakes. [ABSTRACT FROM AUTHOR]

Inland lake water–air interfaces, particularly the partial pressure of CO2 (pCO2), have become key parameters in the study of global carbon cycle changes. However, there are few studies on short-term daily variations in pCO2 in urbanizing lakes. The fluctuations in pCO2 and CO2 fluxes (fCO2) were monitored biweekly on-site for pCO2 assessments during daytime hours (7:00–17:00 CST) from January to September 2020 in an urbanizing lake located in Southwest China. We found a pronounced and uninterrupted decline in the average levels of pCO2 and fCO2 from 7:00 to 17:00 CST. Notably, the mornings (7:00–12:00 CST) exhibited substantially elevated pCO2 and fCO2 values compared to the afternoons. Specifically, compared to 7:00, the mean pCO2 and fCO2 at 17:00 CST decreased by ca. 74% and 112%, respectively. The average daytime pCO2 was 707 ± 642 μatm, significantly higher than the typical atmospheric CO2 levels of 380–420 μatm, while the average pCO2 on 9 January, 1 April, and 27 July was lower than typical atmospheric CO2. Each month, all water environmental parameters showed significant differences. pCO2 and fCO2 reached maximums in September; water temperature and turbidity significantly increased; and pH, dissolved oxygen and transparency markedly decreased. Additionally, the correlation between pCO2 and environmental factors demonstrated that the nutrient levels, dissolved oxygen, pH, and transparency/turbidity had significant roles in CO2 dynamics in this lake. Therefore, this urbanizing lake could serve as a CO2 source and sink during the daytime. [ABSTRACT FROM AUTHOR]