Danish estuaries as coastal filters: identification of hotspots

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Coastal zones are directly exposed to human activities that, among other effects, increase inputs of nutrient and organic matter. Although continuous human alterations might disrupt the subtle ecological balance, coastal ecosystems are to some degree resilient and can absorb changes in these inputs, acting as a filter between land and ocean. In such transition zones, the salinity gradient is critical for a number of biogeochemical processes in the water column and fluxes across the sediment-water interface. Danish estuaries are characterized by receiving freshwater inputs from many scattered streams, yielding relatively high residence times in the near-source environment. Monitoring data from different coastal locations in Denmark indicate that substantial amounts of nitrogen and phosphorus are removed at low salinities, indicating an important sink of nutrients in the vicinities of freshwater sources. Thus, this study aims to identify potential hotspots for the removal of nutrients and organic matter in two coastal zones, Hove Å and Nivå. Spatial variability at the two sites were explored using high frequency sampling of multiple water quality parameters to characterize changes over the salinity gradient with a fine resolution. Distinct salinity gradients characterized the two study sites, with a broader salinity range (0-25) observed in Nivå than in Hove Å (2.5-15). Non-linear relationships with salinity were clearly identified for different parameters (pH, dissolved oxygen, phytoplankton) in Hove Å, indicating intense biological processing in the salinity range 5-10. At Nivå, most of the changes were observed at salinities of 5-15, with more linear relationships between water quality variables and salinity, indicating that simple mixing as the dominant process. Our results suggest that the significance of the coastal filter function may vary broadly among locations, likely reflecting differences in the freshwater inputs and spatial extent of the transition zone.
Original languageEnglish
Publication year2019
Publication statusPublished - 2019
Event20. Danske Havforskermøde - Syddansk Universitet, Odense, Denmark
Duration: 23 Jan 201925 Jan 2019


Conference20. Danske Havforskermøde
LocationSyddansk Universitet
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