Tidally resolved observations of organic carbon exchange through Eastern Long Island Sound

Byrd, Allison; Vlahos, Penny; Whitney, Michael M.; Menniti, Christina; Warren, Joseph K.

doi:10.1016/j.ecss.2019.106463

Cited by 6 publications

(14 citation statements)

References 21 publications

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“…The above-outlined correlations further support the importance of the tidal water in mobilizing sediment-bound Hg into the water column , and the river water in supplying new Hg to the estuary . DOC and POC concentrations also followed the general patterns of THg and MeHg during the three cruises, where higher concentrations were found near the Connecticut River but sometimes also near the bottom . POC and salinity were negatively correlated ( R = −0.20, P = 0.048*), while an opposite pattern existed between salinity and DOC ( R = 0.57, P < 0.01**, Figures and S4), suggesting different major sources of POC and DOC.…”

Section: Resultssupporting

confidence: 54%

“…Microbial degradation of terrestrial DOC was previously proposed as the fuel for MeHg production as both DOC concentrations and methylation rates were found to be highest near the river in the overall stratified estuary, but we have not found such a pattern. Additionally, DOC levels in the surface waters of the sub-Arctic fjord were approximately twofold higher than those in LIS during our sampling cruises . The modeling results indicated that DOC in LIS was dominated by autochthonous sources, although there was significant interannual variation .…”

Section: Resultsmentioning

confidence: 65%

“…During the three cruises, other oceanographic measurements, such as temperature, salinity, and dissolved oxygen, were measured using a Seabird SBE 19 conductivity temperature depth profiler. The data are mentioned in our previous study …”

Section: Methodsmentioning

confidence: 99%

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Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Liu,

Mason,

Vlahos

et al. 2023

Environ. Sci. Technol.

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Estuaries are an important food source for the world's growing population, yet human health is at risk from elevated exposure to methylmercury (MeHg) via the consumption of estuarine fish. Moreover, the sources and cycling of MeHg in temperate estuarine ecosystems are poorly understood. Here, we investigated the seasonal and tidal patterns of mercury (Hg) forms in Long Island Sound (LIS), in a location where North Atlantic Ocean waters mix with the Connecticut River. We found that seasonal variations in Hg and MeHg in LIS followed the extent of riverine Hg delivery, while tides further exacerbated the remobilization of earlier deposited riverine Hg. The net production of MeHg near the river plume was significant compared to that in other locations and enhanced during high tide, possibly resulting from the enhanced microbial activity and organic carbon remineralization in the river plume. Statistical models, driven by our novel data, further support the hypothesis that the river-delivered organic matter and inorganic Hg drive net MeHg production in the estuarine water column. Our study sheds light on the significance of water column biogeochemical processes in temperate tidal estuaries in regulating MeHg levels and inspires new questions in our quest to understand MeHg sources and dynamics in coastal oceans.

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Section: Resultssupporting

confidence: 54%

Section: Resultsmentioning

confidence: 65%

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Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Liu,

Mason,

Vlahos

et al. 2023

Environ. Sci. Technol.

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“…Although the tidal flat (i.e., habitat IV) has no higher plants, the SOC and TN contents and storage below the 30 cm depth were slightly higher than those in habitats II and III. There are three factors concerned: (a) the effect of salting‐out is enhanced, which may lower the metabolic capacity of microorganisms and thus decrease the rate of SOC decomposition in a high‐saline environment (Figure 6a; Chambers et al., 2013; Stagg et al., 2018); (b) the increased proportions of C derived from tidally induced marine input (Byrd et al., 2019); and (c) the transportation and sedimentation of organic‐bearing particles from the upstream also contributed to SOM accumulation in the tidal flat. On a long time scale, pH and EC were the direct factors affecting SOC contents in topsoil (0–40 cm) and subsoil (40–100 cm), respectively (Figure S4).…”

Section: Discussionmentioning

confidence: 99%

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ¹³C‐δ¹⁵N, and lignin biomarker

Xia

Song

et al. 2020

Global Change Biology

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Despite increasing recognition of the critical role of coastal wetlands in mitigating climate change, sea‐level rise, and salinity increase, soil organic carbon (SOC) sequestration mechanisms in estuarine wetlands remain poorly understood. Here, we present new results on the source, decomposition, and storage of SOC in estuarine wetlands with four vegetation types, including single Phragmites australis (P, habitat I), a mixture of P. australis and Suaeda salsa (P + S, habitat II), single S. salsa (S, habitat III), and tidal flat (TF, habitat IV) across a salinity gradient. Values of δ13C increased with depth in aerobic soil layers (0–40 cm) but slightly decreased in anaerobic soil layers (40–100 cm). The δ15N was significantly enriched in soil organic matter at all depths than in the living plant tissues, indicating a preferential decomposition of 14N‐enriched organic components. Thus, the kinetic isotope fractionation during microbial degradation and the preferential substrate utilization are the dominant mechanisms in regulating isotopic compositions in aerobic and anaerobic conditions, respectively. Stable isotopic (δ13C and δ15N), elemental (C and N), and lignin composition (inherited (Ad/Al)s and C/V) were not completely consistent in reflecting the differences in SOC decomposition or accumulation among four vegetation types, possibly due to differences in litter inputs, root distributions, substrate quality, water‐table level, salinity, and microbial community composition/activity. Organic C contents and storage decreased from upstream to downstream, likely due to primarily changes in autochthonous sources (e.g., decreased onsite plant biomass input) and allochthonous materials (e.g., decreased fluvially transported upland river inputs, and increased tidally induced marine algae and phytoplankton). Our results revealed that multiple indicators are essential to unravel the degree of SOC decomposition and accumulation, and a combination of C:N ratios, δ13C, δ15N, and lignin biomarker provides a robust approach to decipher the decomposition and source of sedimentary organic matter along the river‐estuary‐ocean continuum.

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“…LIS total organic C concentrations increase with point-source wastewater discharge volume (Mullaney 2015 ), terrestrially-loaded freshwater flow (Walsh 1995 ), overall anthropogenic N-inputs (NYSDEC 2000 ), and precipitation (in surface waters; Willey et al 2000 ) leading to ~25% of LIS oxygen consumption from the oxidation of organic C (NYSDEC 2000 ). Rivers and marshes supply substantial, though temporally variable, DOC to LIS, with a net DOC import generally during low flow years, a net export to the continental shelf during average/high flow years (Vlahos and Whitney 2017 ; Byrd et al 2020 ; Supino 2020 ), and most DOC removed via photo-oxidation (Zhong and Wang 2009 ). As such, terrestrial sources of labile and overall organic C levels have increased within WLIS (Varekamp 2010 ) coincident with a general rise in DOC concentrations throughout Northern U.S. surface waters (Evans et al 2005 ).…”

Section: Introductionmentioning

confidence: 99%

Transitions in nitrogen and organic matter form and concentration correspond to bacterial population dynamics in a hypoxic urban estuary

et al. 2023

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Nitrogen (N) inputs to developed coastlines are linked with multiple ecosystem and socio-economic impacts worldwide such as algal blooms, habitat/resource deterioration, and hypoxia. This study investigated the microbial and biogeochemical processes associated with recurrent, seasonal bottom-water hypoxia in an urban estuary, western Long Island Sound (WLIS), that receives high N inputs. A 2-year (2020–2021) field study spanned two hypoxia events and entailed surface and bottom depth water sampling for dissolved nutrients as inorganic N (DIN; ammonia-N and nitrite + nitrate (N + N)), organic N, orthophosphate, organic carbon (DOC), as well as chlorophyll a and bacterial abundances. Physical water quality data were obtained from concurrent conductivity, temperature, and depth casts. Results showed that dissolved organic matter was highest at the most-hypoxic locations, DOC was negatively and significantly correlated with bottom-water dissolved oxygen (Pearson’s r = −0.53, p = 0.05), and ammonia-N was the dominant DIN form pre-hypoxia before declining throughout hypoxia. N + N concentrations showed the reverse, being minimal pre-hypoxia then increasing during and following hypoxia, indicating that ammonia oxidation likely contributed to the switch in dominant DIN forms and is a key pathway in WLIS water column nitrification. Similarly, at the most hypoxic sampling site, bottom depth bacteria concentrations ranged ~ 1.8 × 10 4 –1.1 × 10 5 cells ml −1 pre-hypoxia, declined throughout hypoxia, and were positively and significantly correlated (Pearson’s r = 0.57; p = 0.03) with ammonia-N, confirming that hypoxia influences N-cycling within LIS. These findings provide novel insight to feedbacks between major biogeochemical (N and C) cycles and hypoxia in urban estuaries. Supplementary Information The online version contains supplementary material available at 10.1007/s10533-023-01021-2.

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Tidally resolved observations of organic carbon exchange through Eastern Long Island Sound

Cited by 6 publications

References 21 publications

Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ¹³C‐δ¹⁵N, and lignin biomarker

Transitions in nitrogen and organic matter form and concentration correspond to bacterial population dynamics in a hypoxic urban estuary

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Tidally resolved observations of organic carbon exchange through Eastern Long Island Sound

Cited by 6 publications

References 21 publications

Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Riverine Discharge Fuels the Production of Methylmercury in a Large Temperate Estuary

Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ13C‐δ15N, and lignin biomarker

Transitions in nitrogen and organic matter form and concentration correspond to bacterial population dynamics in a hypoxic urban estuary

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Distribution, sources, and decomposition of soil organic matter along a salinity gradient in estuarine wetlands characterized by C:N ratio, δ¹³C‐δ¹⁵N, and lignin biomarker