| Summary: | Climate change driven increases in temperature are enhancing land-ocean connectivity in the coastal Arctic, with a range of implications for coastal food-webs and contaminant cycling. Terrestrial inputs are a direct source of carbon and legacy contaminants to coastal areas, but as a source of freshwater, nutrients and suspended inorganic sediments, they can also affect coastal food-webs and contaminant cycling indirectly through impacts on phytoplankton community structure and contaminant removal and burial. To investigate coastal responses to terrestrial inputs, we conducted a field study in a river- and glacier- influenced Arctic fjord system (Isfjorden, Svalbard), in May, June and August, 2018 with a follow-up study in 2019. Environmental data, zooplankton and benthos were collected from 17 fjord stations along transects from river estuaries and glacier fronts to the outer fjord. Fauna were analyzed for persistent organic pollutants and dietary carbon sources were assessed using a variety of biogeochemical tracer techniques, including fatty acid trophic markers and bulk stable isotopes. Our observations revealed a pervasive freshwater footprint in the inner fjord arms, the geochemical properties of which varied spatially and seasonally as the melt season progressed from snowmelt in June to glacial melt and permafrost runoff in August. Zooplankton fatty acid profiles were strongly coupled to fatty acid profiles of water column particulate organic matter, reflecting seasonal and spatial shifts in phytoplankton community structure, with elevated contributions of diatom fatty acids in May following the spring phytoplankton bloom, to dinoflagellate and terrestrial fatty acids in June and August when high sediment loads attenuate light in the nearshore. Persistent organic pollutant concentrations in coastal fauna were inversely related to terrestrial inputs spatially and seasonally, suggesting that freshwater and associated high rates of inorganic sedimentation act to dilute, bind and bury persistent organic pollutants in the inner fjord arms of Isfjorden. Our results highlight the physical, chemical and biological impact of terrestrial inputs on downstream coastal ecosystems in a rapidly changing Arctic environment.
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