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1. Marine and Not Terrestrial Resources Support Nearshore Food Webs Across a Gradient of Glacial Watersheds in the Northern Gulf of Alaska

   https://doi.org/10.1007/s12237-023-01277-9  

   Schloemer, James; Munk, Lee Ann; Iken, Katrin (October 2023, Estuaries and Coasts)

   Abstract Estuaries are among the most productive ecosystems on Earth, yet they are at risk in high-latitude regions due to climate-driven effects on the connected terrestrial and marine realms. Northern Hemisphere warming exceeds the global average and accelerates the melting of glaciers. As a result, the magnitude of freshwater discharge into estuaries may increase during the peak in glacial meltwater, ultimately affecting the riverine flux of organic matter (OM) from the land to coastal environments and food webs within. We investigated the extent to which terrestrial OM subsidizes nearshore food webs in northern Gulf of Alaska watersheds and if differences in the relative proportion of terrestrial versus marine OM supporting these food webs are explained by watershed glacial cover and/or by seasonal glacial discharge regimes. A stable isotope mixing model was employed to determine the contribution of marine (phytoplankton, macroalgae) and terrestrial (vascular plant) sources to the diets of grazing/detritivore and filter/suspension-feeding coastal invertebrates at the outflows of watersheds of varying glacial influence and across three distinct discharge periods. Additionally, a distance-based redundancy analysis was conducted to investigate the effects of watershed-characteristic (e.g., slope, vegetation cover) sourcing and transport of terrestrial OM on consumer diets. The diets of both feeding groups were predominantly marine (> 90%) and varied little among estuarine study sites at watersheds of different glacial cover or glacial discharge periods. Our findings suggest that terrestrial OM is not readily used by nearshore food webs in this productive study system, presumably due to the high quantity and quality of available marine OM. 

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2. Patterns and Drivers of Carbon Dioxide Concentrations in Aquatic Ecosystems of the Arctic Coastal Tundra

   https://doi.org/10.1029/2020GB006552  

   Lougheed, V. L.; Tweedie, C. E.; Andresen, C. G.; Armendariz, A. M.; Escarzaga, S. M.; Tarin, G. (March 2020, Global Biogeochemical Cycles)

   Abstract Multiple aquatic ecosystems (pond, lake, river, lagoon, and ocean) on the Arctic Coastal Plain near Utqiaġvik, Alaska, USA, were visited to determine their relative atmospheric CO₂flux and how this may have changed over time. The nearshore coastal waters and large freshwater lakes were small sources of atmospheric CO₂, whereas smaller waterbodies were substantial sources.pCO₂was linked to dissolved organic carbon concentrations across broad spatial and temporal scales, with greater concentrations found in smaller freshwater systems (i.e., ponds and rivers). On a day‐to‐day basis, water temperatures appeared to be the strongest driver ofpCO₂levels in tundra ponds, where warmer temperatures likely stimulated microbial mineralization of carbon in both aquatic and hydrologically linked terrestrial environments. Large rainfall events, which may lead to inflow of carbon‐rich groundwater into these ponds, also were associated with increased daily averagepCO₂. Based on comparison to historical data, we estimate that CO₂concentrations in tundra ponds have increased more than 1.8 times over the past 40 years. Quantifying CO₂flux from these abundant aquatic ecosystems on the Arctic Coastal Plain and elsewhere in the high northern latitudes will likely have important implications for furthering understanding of landscape‐level and nearshore carbon dynamics in the Arctic. 

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3. Demonstrating a High‐Resolution Gulf of Alaska Ocean Circulation Model Forced Across the Coastal Interface by High‐Resolution Terrestrial Hydrological Models

   https://doi.org/10.1029/2019JC015724  

   Danielson, Seth L.; Hill, David F.; Hedstrom, Katherine S.; Beamer, Jordan; Curchitser, Enrique (August 2020, Journal of Geophysical Research: Oceans)

   Abstract We demonstrate a linking of moderately high resolution (1 km) terrestrial hydrological models to a 3‐D ocean circulation model having similar resolution in the northern Gulf of Alaska, where a distributed line source of freshwater runoff exerts strong influence over the shelf's hydrographic structure and flow dynamics. The model interfacing is accomplished via mass flux boundary conditions through the ocean model coastal wall at all land‐ocean adjoining grid cells. Despite the high runoff volume and lack of a coastal mixing estuary, the implementation maintains numerical stability by prescribing depth invariant and surface‐intensified inflows at fast and slow discharge grid cells, respectively. Based on comparisons against in situ hydrographic data, the coastal sidewall mass flux boundary condition results in more realistic hindcast surface salinity and salinity gradient fields than models that distribute coastal runoff in the form of spatially distributed precipitation. Correlations with observed thermal and haline monthly anomalies reveal statistically significant hindcast temporal variability during the freshet season when the signal‐to‐noise ratio is large. Comparisons of ocean models forced by high‐ and low‐resolution hydrological models reveal differences in salinity, surface elevation, and velocity fields, highlighting the value and importance of accurate coastal runoff fields. The model results improve our understanding of the regional influence of runoff on sea level elevations and the distribution and fate of fresh water. Our approach has potential applications to biogeochemical modeling in regions where distributed line source freshwater coastal discharges deliver heat, momentum, and chemical constituents that may influence the marine carbon pump. 

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4. An ASBPA White Paper: Human and ecosystem health in coastal systems

   https://doi.org/10.34237/1009018  

   Elko, Nicole; Foster, Diane; Kleinheinz, Gregory; Raubenheimer, Britt; Brander, Susanne; Kinzelman, Julie; Kritzer, Jacob; Munroe, Daphne; Storlazzi, Curt; Sutula, Martha; et al (February 2022, Shore & Beach)

   U.S. coastal economies and communities are facing an unprecedented and growing number of impacts to coastal ecosystems including beach and fishery closures, harmful algal blooms, loss of critical habitat, as well as shoreline damage. This paper synthesizes our present understanding of the dynamics of human and ecosystem health in coastal systems with a focus on the need to better understand nearshore physical process interactions with coastal pollutants and ecosystems (e.g. fate and transport, circulation, depositional environment, climate change). It is organized around two major topical areas and six subtopic areas: 1) Identifying and mitigating coastal pollutants, including fecal pollution, nutrients and harmful algal blooms, and microplastics; and 2) Resilient coastal ecosystems, which focuses on coastal fisheries, shellfish and natural and nature-based features (NNBF). Societal needs and the tools and technologies needed to address them are discussed for each subtopic. Recommendations for scientific research, observations, community engagement, and policies aim to help prioritize future research and investments. A better understanding of coastal physical processes and interactions with coastal pollutants and resilient ecosystems (e.g. fate and transport, circulation, depositional environment, climate change) is a critical need. Other research recommendations include the need to quantify potential threats to human and ecosystem health through accurate risk assessments and to quantify the resulting hazard risk reduction of natural and nature-based features; improve pollutant and ecosystem impacts forecasting by integrating frequent and new data points into existing and novel models; collect environmental data to calibrate and validate models to predict future impacts on coastal ecosystems and their evolution due to anthropogenic stressors (land-based pollution, overfishing, coastal development), climate change, and sea level rise; and develop lower cost and rapid response tools to help coastal managers better respond to pollutant and ecosystem threats. 

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5. Systematic Quantification of Nearshore and Offshore Submarine Groundwater Discharge Along Florida Coasts

   https://doi.org/10.1029/2025JC022597  

   Howlader, Rakib; Liu, Weibo; Ye, Ming; Wei, Minghan; Haque, Marjena Beantha; Zhang, Xiaolang (July 2025, Journal of Geophysical Research: Oceans)

   Abstract Submarine groundwater discharge (SGD), comprising both nearshore and offshore components, plays a vital role in water cycling and solute transport in coastal areas, and affects coastal marine ecosystems. Previous estimations of SGD based on seepage meters, geochemical tracers, water balances, analytical, and numerical approaches frequently overlooked offshore contributions driven by oceanic currents, waves, and tides, resulting in an incomplete understanding of SGD dynamics and its ecological consequences. Therefore, this study quantified the total SGD by integrating offshore (current‐, wave‐, and tide‐driven SGD) and nearshore (fresh SGD and tide‐driven SGD) components in Florida coasts. The calculated total SGD was approximately 15.08% of annual precipitation volume in Florida, with 14.09% offshore SGD (0.7%, 8.2%, and 5.2% from currents, waves, and tides, respectively) and ∼0.986% nearshore SGD (0.44% and 0.55% from fresh and recirculated SGD), underscoring offshore SGD as a major driver of groundwater discharge extending across the continental shelf. Moreover, nearshore SGD‐derived dissolved inorganic nutrient fluxes were estimated as kg/yr for nitrogen and kg/yr for phosphorus, whereas offshore SGD‐derived nutrients were kg/yr for nitrogen and kg/yr for phosphorus. On average, these nutrient inputs were approximately 6 and 4 times greater than those from surface water nutrient fluxes from coastal river discharge for dissolved inorganic nitrogen and dissolved inorganic phosphorus, respectively, highlighting the significant role of SGD in nutrient cycling in Florida. Additionally, we identified 54 SGD hotspots, which are generally aligned spatially with the distribution of coastal springs. Therefore, future research should evaluate the impact on nutrient loads to enhance coastal water management and sustainability. 

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