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1. Storm-Driven Fresh Submarine Groundwater Discharge and Nutrient Fluxes From a Barrier Island

   https://doi.org/10.3389/fmars.2021.679010  

   Adyasari, Dini ; Montiel, Daniel ; Mortazavi, Behzad ; Dimova, Natasha ( July 2021 , Frontiers in Marine Science)

   null (Ed.)

   Quantifying and characterizing groundwater flow and discharge from barrier islands to coastal waters is crucial for assessing freshwater resources and contaminant transport to the ocean. In this study, we examined the groundwater hydrological response, discharge, and associated nutrient fluxes in Dauphin Island, a barrier island located in the northeastern Gulf of Mexico. We employed radon ( 222 Rn) and radium (Ra) isotopes as tracers to evaluate the temporal and spatial variability of fresh and recirculated submarine groundwater discharge (SGD) in the nearshore waters. The results from a 40-day continuous 222 Rn time series conducted during a rainy season suggest that the coastal area surrounding Dauphin Island was river-dominated in the days after storm events. Groundwater response was detected about 1 week after the precipitation and peak river discharge. During the period when SGD was a factor in the nutrient budget of the coastal area, the total SGD rates were as high as 1.36 m day –1 , or almost three times higher than detected fluxes during the river-dominated period. We found from a three-endmember Ra mixing model that most of the SGD from the barrier island was composed of fresh groundwater. SGD was driven by marine and terrestrial forces, and focused on the southeastern part of the island. We observed spatial variability of nutrients in the subterranean estuary across this part of the island. Reduced nitrogen (i.e., NH 4 + and dissolved organic nitrogen) fluxes dominated the eastern shore with average rates of 4.88 and 5.20 mmol m –2 day –1 , respectively. In contrast, NO 3 – was prevalent along the south-central shore, which has significant tourism developments. The contrasting nutrient dynamics resulted in N- and P-limited coastal water in the different parts of the island. This study emphasizes the importance of understanding groundwater flow and dynamics in barrier islands, particularly those urbanized, prone to storm events, or located near large estuaries. 

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2. Linking Seasonal Changes in Organic Matter Composition and Nutrients to Shifting Hydraulic Gradients in Coastal Urban Canals

   https://doi.org/10.1029/2022WR033334  

   Smith, Matthew A. ; Kominoski, J. S. ; Price, R. M. ; Abdul‐Aziz, O. I. ; Troxler, T. G. ( February 2023 , Water Resources Research)

   The capacity for coastal river networks to transport and transform dissolved organic matter (DOM) is widely accepted. However, climate‐induced shifts in stormwater runoff and tidal extension alter fresh and marine water source contributions, associated DOM, and processing rates of nutrients entering coastal canals. We investigate how time‐variable interactions among coastal water source contributions influence the concentrations of dissolved organic carbon (DOC), nutrients, and DOM composition in urban canals. We quantified the spatiotemporal variability of DOM quality and nutrient concentrations to determine contributions of tidal marine water, rainwater, stormwater runoff, and groundwater to three coastal urban canals of Miami, Florida (USA). We created a Bayesian Monte Carlo mixing model using measurements of fluorescent DOM (fDOM), DOC concentrations, δ¹⁸O and δ²H isotopic signatures, and chloride (Cl⁻). Fractional contributions of groundwater averaged 17% in the dry season and 26% at peak high tide during the subtropical wet season (September–November). The canal‐to‐marine head difference (CMHD) was a primary driver of groundwater contributions to coastal urban canals and monthly patterns of fDOM/DOC. High tide (>1 m) and discharge events were found to connect canals to upstream sources of terrestrial DOM. Loading of terrestrially sourced DOC and DOM is pulsed to urban canals, shunted downstream and supplemented by microbially sourced DOM during the wet season at high tide. Overall, we demonstrate that a combined tracer approach with isotopes and fDOM can help identify groundwater contributions to coastal waterways and that autochthonous fDOM may prime the degradation of carbon or nutrients as the CMHD pushes inland.

    

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3. Freeze–thaw processes and intense rainfall: the one-two punch for high sediment and nutrient loads from mid-Atlantic watersheds

   https://doi.org/10.1007/s10533-017-0417-7  

   Inamdar, Shreeram ; Johnson, Erin ; Rowland, Richard ; Warner, Daniel ; Walter, Robert ; Merritts, Dorothy ( April 2018 , Biogeochemistry)

   Large runoff, sediment, and nutrient exports from watersheds could occur due to individual extreme climate events or a combination of multiple hydrologic and meteorological conditions. Using high-frequency hydrologic, sediment, and turbidity data we show that freeze–thaw episodes followed by intense winter (February) rainstorms can export very high concentrations and loads of suspended sediment and particulate organic carbon (POC) and nitrogen (PN) from mid-Atlantic watersheds in the US. Peak suspended sediment (> 5000 mg L−1), POC (> 250 mg L−1) and PN (> 15 mg L−1) concentrations at our 12 and 79 ha forested watersheds for the February rainfall-runoff events were highest on record and the fluxes were comparable to those measured for tropical storms. Similar responses were observed for turbidity values (> 400 FNU) at larger USGS-monitored watersheds. Much of the sediments and particulate nutrients likely originated from erosion of stream bank sediments and/or channel storage. Currently, there is considerable uncertainty about the contribution of these sources to nonpoint source pollution, particularly, in watersheds with large legacy sediment deposits. Future climate projections indicate increased intensification of storm events and increased variability of winter temperatures. Freeze–thaw cycles coupled with winter rain events could increase erosion and transport of streambank sediments with detrimental consequences for water quality and health of downstream aquatic ecosystems. 

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4. Benthic cyanobacteria of the genus Nostoc are a source of microcystins in Greenlandic lakes and ponds

   https://doi.org/10.1111/fwb.13636  

   Trout‐Haney, Jessica V. ; Ritger, Amelia L. ; Cottingham, Kathryn L. ( October 2020 , Freshwater Biology)

   Benthic primary producers are recognised for their important role in contributing to ecosystem productivity and nutrient cycling in lake and stream ecosystems, particularly in polar environments. In Arctic lakes, benthic producers often comprise mats or colonies of cyanobacteria capable of producing cyanotoxins. However, the extent to which benthic communities contribute cyanotoxins in polar regions remains poorly described.

   We evaluated the potential for benthic colonies of the cyanobacteriumNostoc pruniformefrom lakes in Kangerlussuaq, Greenland, to contribute microcystins (MCs) to lake water using three approaches. First, we dissected field‐collectedNostoccolonies and measured MCs within multiple layers of fresh colony tissue. Second, we conducted a laboratory experiment to evaluate the temporal dynamics of MC release by incubated, intact colonies. Finally, we quantified whether MC concentrations in water and sediment samples in the field were higher in and above dense bands of benthicNostocas compared to bare sediment.

   Field‐collectedNostoccolonies contained MCs throughout the colony tissue, suggesting that damage to colonies from grazers or physical disturbance could facilitate the release of toxins into the water. UndamagedNostoccolonies incubated in high‐nutrient conditions in the laboratory leaked MCs into the surrounding water at a steady mass‐specific rate over the course of 7 days.

   Microcystin concentrations in water and sediment from two Greenlandic lakes were highly variable, but slightly higher in lake water immediately above dense bands ofNostocthan in water immediately above bare sediments, suggesting that benthicNostoccolonies contribute cyanotoxins to lake water and that MCs vary at very fine, 1–2 m spatial scales.

   Benthic cyanobacteria may be important in releasing MCs into aquatic ecosystems, especially in systems where benthic producers dominate, such as polar environments.

    

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5. On a Reef Far, Far Away: Anthropogenic Impacts Following Extreme Storms Affect Sponge Health and Bacterial Communities

   https://doi.org/10.3389/fmars.2021.608036  

   Shore, Amanda ; Sims, Jordan A. ; Grimes, Michael ; Howe-Kerr, Lauren I. ; Grupstra, Carsten G. ; Doyle, Shawn M. ; Stadler, Lauren ; Sylvan, Jason B. ; Shamberger, Kathryn E. ; Davies, Sarah W. ; et al ( April 2021 , Frontiers in Marine Science)

   null (Ed.)

   Terrestrial runoff can negatively impact marine ecosystems through stressors including excess nutrients, freshwater, sediments, and contaminants. Severe storms, which are increasing with global climate change, generate massive inputs of runoff over short timescales (hours to days); such runoff impacted offshore reefs in the northwest Gulf of Mexico (NW GoM) following severe storms in 2016 and 2017. Several weeks after coastal flooding from these events, NW GoM reef corals, sponges, and other benthic invertebrates ∼185 km offshore experienced mortality (2016 only) and/or sub-lethal stress (both years). To assess the impact of storm-derived runoff on reef filter feeders, we characterized the bacterial communities of two sponges, Agelas clathrodes and Xestospongia muta , from offshore reefs during periods of sub-lethal stress and no stress over a three-year period (2016—2018). Sponge-associated and seawater-associated bacterial communities were altered during both flood years. Additionally, we found evidence of wastewater contamination (based on 16S rRNA gene libraries and quantitative PCR) in offshore sponge samples, but not in seawater samples, following these flood years. Signs of wastewater contamination were absent during the no-flood year. We show that flood events from severe storms have the capacity to reach offshore reef ecosystems and impact resident benthic organisms. Such impacts are most readily detected if baseline data on organismal physiology and associated microbiome composition are available. This highlights the need for molecular and microbial time series of benthic organisms in near- and offshore reef ecosystems, and the continued mitigation of stormwater runoff and climate change impacts. 

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