Land-Ocean Interactions in a Changing Arctic: Effects of terrestrial inputs on coastal food-web carbon source and contamination in Isfjorden, Svalbard

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

Terrestrial Inputs Shape Coastal Bacterial and Archaeal Communities in a High Arctic Fjord (Isfjorden, Svalbard)

The Arctic is experiencing dramatic changes including increases in precipitation, glacial melt, and permafrost thaw, resulting in increasing freshwater runoff to coastal waters. During the melt season, terrestrial runoff delivers carbon- and nutrient-rich freshwater to Arctic coastal waters, with unknown consequences for the microbial communities that play a key role in determining the cycling and fate of terrestrial matter at the land-ocean interface. To determine the impacts of runoff on coastal microbial (bacteria and archaea) communities, we investigated changes in pelagic microbial community structure between the early (June) and late (August) melt season in 2018 in the Isfjorden system (Svalbard). Amplicon sequences of the 16S rRNA gene were generated from water column, river and sediment samples collected in Isfjorden along fjord transects from shallow river estuaries and glacier fronts to the outer fjord. Community shifts were investigated in relation to environmental gradients, and compared to river and marine sediment microbial communities. We identified strong temporal and spatial reorganizations in the structure and composition of microbial communities during the summer months in relation to environmental conditions. Microbial diversity patterns highlighted a reorganization from rich communities in June toward more even and less rich communities in August. In June, waters enriched in dissolved organic carbon (DOC) provided a niche for copiotrophic taxa including Sulfitobacter and Octadecabacter. In August, lower DOC concentrations and Atlantic water inflow coincided with a shift toward more cosmopolitan taxa usually associated with summer stratified periods (e.g., SAR11 Clade Ia), and prevalent oligotrophic marine clades (OM60, SAR92). Higher riverine inputs of dissolved inorganic nutrients and suspended particulate matter also contributed to spatial reorganizations of communities in August. Sentinel taxa of this late summer fjord environment included taxa from the class Verrucomicrobiae (Roseibacillus, Luteolibacter), potentially indicative of a higher fraction of particle-attached bacteria. This study highlights the ecological relevance of terrestrial runoff for Arctic coastal microbial communities and how its impacts on biogeochemical conditions may make these communities susceptible to climate change

Seasonal riverine inputs may affect diet and mercury bioaccumulation in Arctic coastal zooplankton

Climate change driven increases in permafrost thaw and terrestrial runoff are expected to facilitate the mobilization and transport of mercury (Hg) from catchment soils to coastal areas in the Arctic, potentially increasing Hg exposure of marine food webs. The main aim of this study was to determine the impacts of seasonal riverine inputs on land-ocean Hg transport, zooplankton diet and Hg bioaccumulation in an Arctic estuary (Adventfjorden, Svalbard). The Adventelva River was a source of dissolved and particulate Hg to Adventfjorden, especially in June and July during the river's main discharge period. Stable isotope and fatty acid analyses suggest that zooplankton diet varied seasonally with diatoms dominating during the spring phytoplankton bloom in May and with increasing contributions of dinoflagellates in the summer months. In addition, there was evidence of increased terrestrial carbon utilization by zooplankton in June and July, when terrestrial particles contributed substantially to the particulate organic matter pool. Total (TotHg) and methyl Hg (MeHg) concentrations in zooplankton increased from April to August related to increased exposure to riverine inputs, and to shifts in zooplankton diet and community structure. Longer and warmer summer seasons will probably increase riverine runoff and thus Hg exposure to Arctic zooplankton.Seasonal riverine inputs may affect diet and mercury bioaccumulation in Arctic coastal zooplanktonpublishedVersio

Three decades of change in the Skagerrak coastal ecosystem, shaped by eutrophication and coastal darkening

Global coastal ecosystems are under accelerating pressure from human activities and climate change. In this study we explore a long-term time series (mostly 1990–2016) from major Norwegian rivers, together with coastal time series from the Norwegian Skagerrak coast. The aims are to: 1) analyse long-term trends in riverine loadings to Skagerrak, changes in coastal water quality and pelagic and benthic species composition, and 2) to describe the relationships between human drivers (eutrophication and coastal darkening) and community structure of benthic communities. Riverine discharge and transport increased by 23–85% over the time period, corresponding to a 40–78% increase in concentrations of suspended particulate material in coastal waters and reduced surface salinity, connected to the reported coastal darkening of coastal waters. There was a worsening in ecological status for hard-bottom benthic communities (0–30 m) and a reduction in the lower growth depth limit of several macroalgae species. A structural shift in the community composition from macroalgae towards increased abundance of animals was found to be related to coastal darkening and reduced eutrophication. The concentration of coastal inorganic nutrients (DIN, PO4) declined by 27–36%, in response to management efforts to reduce eutrophication in European regional seas. Results indicate that reduced eutrophication was related to increased ecological status of the deep soft-bottom community (350 m), with a reduction in opportunistic polychaetes and an increase in filter feeding bivalves. This work highlights how climate change and other human-induced changes in a boreal ecosystem intensifies land-ocean interactions, and calls for more adaptive monitoring, where traditional water quality programs and policies need to evolve iteratively as new information emerges and the major drivers of the systems change.publishedVersio

Using in situ sensor-based monitoring to study impacts of climate change on river water quality and element fluxes

Prosjektleder: Øyvind KasteThe report contains an analysis of high-frequency sensor data from two rivers included in the Norwegian River Monitoring Programme; Storelva in southern Norway and Målselva in northern Norway. The main aim of the report is to combine in situ sensor-based monitoring data with climate, hydrology and water chemistry data to study impacts of climate change on river water quality and element fluxes. The report also highlights challenges, opportunities and the strong potential for sensor-based monitoring to yield new knowledge related to climate change impacts on river water quality.Norwegian Environment AgencypublishedVersio

Tørke og effekter på vannkvalitet og biota i lite påvirkede vassdrag i Norge

Prosjektleder Jan-Erik ThraneI denne rapporten har vi har vi brukt overvåkingsdata fra lite påvirkede vassdrag for å studere effekter av tørke på vannkvalitet og biota. Vi sammenliknet vannkjemiske og biologiske data fra tørkesommeren 2018 (som våre analyser bekrefter at var historisk tørr og varm) med resultater fra de samme elvene i det mer «normale» året 2020. Resultatene viste få klare effekter på vannkjemi, med unntak av tydelig lavere DOC og fargetall under tørken. Stofftransporten var svært lav under tørken pga. liten vanntransport, med potensielle effekter på nedstrøms innsjøer og kystvann. For bunndyr fant vi ingen effekter på indekser som responderer på vanntemperatur, vannføring eller oksygeninnhold. Dette skyldes nok at prøvene tas i strykpartier, der forholdene er gode selv under ekstrem tørke. Faktorer som redusert vanndekt areal og høy vanntemperatur forventes allikevel å påvirke bunndyr, men ble ikke fanget opp med standard prøvetakingsmetodikk. Tørkesommeren 2018 hadde begrenset påvirkning på bestandene av ung laksefisk. Nasjonalt var det få trender fra 2017 til 2019 (altså før og etter tørkesommeren) eller i sammenlikningen av 2018 og 2020, men i Midt-Norge var det en nedgang i tetthet og gjennomsnittsstørrelse fra 2017 til 2019.MiljødirektoratetpublishedVersio

Hyperbenthic Food-Web Structure in Kongsfjord: A Two-Season Comparison using Stable Isotopes and Fatty Acids.

Current knowledge of the Arctic marine ecosystem is based primarily on studies performed during the polar day on the pelagic and benthic realms. Both the polar night and the hyperbenthic layer remain substantial knowledge gaps in the understanding of the marine system at high latitudes. To help address these knowledge gaps, this project investigates the hyperbenthic food web structure in Kongsfjord, a high-latitude, ice-free fjord, in September and January. The hyperbenthic food web was analyzed using a multi-biomarker approach including carbon and nitrogen stable isotopic signatures as well as fatty acid profiles of a variety of hyperbenthic taxa. Results suggest no difference in biomarker composition between September and January, although fatty acid profiles reveal a division in the community between pelagic and benthic consumers. Suggestions for seasonal similarities include slow turnover of stable isotopes and fatty acids in consumer tissue, as well as an increase in dependence on microbial-detrital food webs during the polar night

Riverine impacts on benthic biodiversity and functional traits: A comparison of two sub-Arctic fjords

Climate change is leading to increases in freshwater discharge to coastal environments with implications for benthic community structure and functioning. Freshwater inputs create strong environmental gradients, which potentially affect the community structure of benthic infauna. In turn, changes in functional trait composition have the potential to affect the processing of terrestrially-derived nutrients and organic matter along the freshwater to marine continuum. We investigated the effects of riverine inputs on benthic community structure, functional traits, taxonomic and functional diversity, and utilization of terrestrial organic matter in two contrasting northern Norwegian fjords. Results of this study revealed extensive impacts of riverine inputs on community structure and functional traits. Communities directly affected by the river were characterized by diminished taxonomic and functional diversity, with species and trait composition indicative of an environment influenced by high sedimentation rates. Large, deep-dwelling, biodiffusors and upward conveyors dominated these communities. High community biomass at the river outlet as well as indications of terrestrial organic matter utilization evidenced by stable isotope analyses, suggest that such river-influenced communities may be important for the cycling of terrestrial carbon and nutrients in the coastal zone.publishedVersio

Terrestrial Inputs Drive Seasonality in Organic Matter and Nutrient Biogeochemistry in a High Arctic Fjord System (Isfjorden, Svalbard)

Climate-change driven increases in temperature and precipitation are leading to increased discharge of freshwater and terrestrial material to Arctic coastal ecosystems. These inputs bring sediments, nutrients and organic matter (OM) across the land-ocean interface with a range of implications for coastal ecosystems and biogeochemical cycling. To investigate responses to terrestrial inputs, physicochemical conditions were characterized in a river- and glacier-influenced Arctic fjord system (Isfjorden, Svalbard) from May to August in 2018 and 2019. 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. In June, during the spring freshet, rivers were a source of dissolved organic carbon (DOC; with concentrations up to 1410 μmol L–1). In August, permafrost and glacial-fed meltwater was a source of inorganic nutrients including NO2 + NO3, with concentrations 12-fold higher in the rivers than in the fjord. While marine OM dominated in May following the spring phytoplankton bloom, terrestrial OM was present throughout Isfjorden in June and August. Results suggest that enhanced land-ocean connectivity could lead to profound changes in the biogeochemistry and ecology of Svalbard fjords. Given the anticipated warming and associated increases in precipitation, permafrost thaw and freshwater discharge, our results highlight the need for more detailed seasonal field sampling in small Arctic catchments and receiving aquatic systems.publishedVersio