Where land meets sea: Effects of terrestrial inputs on contaminant dynamics in Arctic coastal ecosystems (TerrACE)

Arctic coastal ecosystems are in transition, with multiple (often interrelated) stressors leading to substantial environmental change. Thawing permafrost, melting glaciers, changes in precipitation and runoff patterns and land-use changes related to increasing human activity in northern regions can lead to changes in the movement of water, nutrients, organic matter and contaminants across the land-ocean interface. The TerrACE project focused on generating quantitative information about terrestrial inputs to coastal waters in Svalbard, and how these inputs can directly and indirectly affect concentrations of contaminants such as mercury (Hg) and PCBs in affected coastal ecosystems. In 2018, we carried out comprehensive sampling of river and coastal waters and coastal sediments, plankton, benthos, and fish from Isfjorden, Svalbard. Using the samples collected, we have analysed concentrations of organic carbon, nutrients and Hg in river and fjord water and suspended particles. We have also carried out detailed studies on dissolved and particulate organic matter composition/quality. We used passive sampling to measure concentrations of several persistent organic pollutants (POPs) for a subset of river and fjord study sites. We have analysed fjord sediments for grain size, organic carbon content, Hg and POPs including polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB). Through stable isotope (C, N) and fatty acid analysis, we have gained insight into main food sources for pelagic and benthic coastal organisms. This is important for helping us to understand both the degree to which coastal organisms rely on terrestrial energy sources as well as how food web structure impacts contaminant concentrations in Isfjorden's coastal food webs. A broad range of pelagic and benthic food web samples were also analysed for POPs as well as for total and methyl mercury. We took advantage of ongoing field work to collect additional samples along the same study gradients in order to study how terrestrial inputs affect coastal ecosystem structure and function. We have carried out side-projects (both MSc student projects, and value-added collaborations) related to community structure of benthic infauna, zooplankton, and microbial community structure. Through MSc student projects, we have also carried out preliminary studies on bird colonies as potential point sources of nutrients to the coast (Finne et al. 2022), and on food web structure and Hg contamination of a coastal lagoon on Svalbard. We have communicated project results through peer-reviewed publications, MSc theses, presentation at conferences and workshops. The project has had a strong focus on education, with the successful completion of one PhD carried out within the project, as well as 8 completed MSc theses and 1 BSc thesis associated with the project. Some highlights based on project results are included below: 1. We found that terrestrial inputs play a key role in shaping physical and chemical conditions in Isfjorden's coastal waters during the summer melt season. Rivers delivered large amounts of suspended sediment to coastal waters, leading to reduced light availability and higher temperatures. Rivers were also important sources of organic matter (especially during the spring snow melt period) and nutrients (especially during the late melt season). (see McGovern et al. 2020) 2. Rivers were also a significant source of mercury to coastal waters and sediments, however it is less clear to what extent this leads to increased Hg concentrations in coastal biota. (Poste et al., in prep) 3. In contrast to our observations for mercury, inputs from land were not a major source of POPs to coastal waters, sediments, or food webs. For instance, concentrations of PCBs and HCB in riverine suspended sediments and nearshore coastal sediments were much lower than concentrations in sediments from further offshore. Our results suggest a primarily marine source for these contaminants, and suggesting that large influxes of terrestrial particles and high sedimentation rates may serve to dilute concentrations of PCBs and HCB in Svalbard's glacier-influenced coastal waters (see Johansen et al. 2021, McGovern et al. 2022, Skogsberg et al. 2022). 4. Our results indicate that coastal biota do rely to at least some degree of terrestrial energy sources, and that terrestrial inputs have a strong impact on the biochemical composition (and quality) of the particulate organic matter pool in both the sediments and water column (McGovern PhD thesis) In summary, the work carried out in the TerrACE project provided valuable insight into how terrestrial inputs shape coastal water quality, ecology and contaminant cycling on Svalbard. This study has also provided important new knowledge related to Arctic land-ocean interactions and has been an important catalyst for developing new research and collaborations both in Svalbard/Northern Norway and abroad.

The project results are significant for three main reasons: 1) our results suggest that inputs of land play a key role in shaping the coastal environment, with implications for ecosystem structure and function; 2) we show that rivers are an important source of Hg to Svalbard's coastal environment; and 3) in contrast, terrestrial inputs are not a substantial source of POPs to the coast. These results will continue to generate new relevant lines of research related to how climate change is likely to impact Arctic coastal ecosystems. Coastal ecosystems are a key source of food and livelihood for communities across the Arctic, and the potential for climate change and release of contaminants from the thawing cryosphere to lead to increased contamination of coastal food webs is of growing concern. TerrACE has also led to increased interdisciplinary collaboration on Svalbard, and has made a strong contribution to education, training and capacity building in early career researchers.

Arctic coastal ecosystems are in transition, with multiple (often interrelated) stressors leading to substantial and long-term environmental change. Stressors such as climate change (including thawing permafrost, melting glaciers, and changes in precipitation and runoff patterns) and land-use changes related to increasing human activity in northern regions can lead to changes in fluxes of water, nutrients, organic matter and contaminants across the land-ocean interface. The TerrACE project focuses on generating quantitative information about terrestrial inputs to coastal waters in Svalbard, and how these inputs directly and indirectly affect contaminant concentrations in affected coastal ecosystems. Key project components include: 1) characterization of riverine water chemistry (including nutrients, organic matter, and contaminants) in the Isfjorden region of Svalbard, 2) a detailed survey of physicochemical conditions (and abiotic contaminant concentrations) along gradients in the influence of terrestrial inputs (i.e. river-fjord and glacier-fjord transects, and sites adjacent to seabird colonies), 3) a quantitative assessment of the effect of terrestrial inputs on energy and contaminant flow through coastal food webs, and 4) the development of a spatially applied Bayesian Network model tool describing the direct and indirect effects of terrestrial inputs on contaminant accumulation in coastal food webs. Through this combination of field-based and modelling approaches, the TerrACE project will provide critical insight into the complex interplay between terrestrial inputs to coastal waters and coastal biogeochemistry, ecology, and contaminant dynamics, and will provide novel modelling tools for monitoring, management and protection of Arctic coastal ecosystems.