Energy flow through the SE Kattegat: A comparative examination of the eutrophication of a coastal marine ecosystem

Seafloor ecological functioning over two decades of organic enrichment

Climate change and anthropogenic nutrient enrichment are driving rapid increases in ocean deoxygenation. These changes cause biodiversity loss and have severe consequences for marine ecosystem functioning and in turn the delivery of ecosystem services upon which humanity depends (e.g. fisheries). We seek to understand how such changes will impact seafloor functioning using biological traits analysis. Results from a sewage-sludge disposal site in the Firth of Clyde, UK spanning 26 years of monitoring showed that substantial changes in macrobenthic nutrient cycling and the provision of food for predators occurred, with elevated functioning on the margins 1-2 km from the centre of the disposal grounds. Thus, changes in food-web dynamics are expected, that weaken benthic pelagic coupling and lower secondary production (such as fisheries). Generally, functioning was conserved, but declined below a ~6% total organic carbon threshold. Similar to other severely deoxygenated systems, the recovery was slow and hysteresis was apparent.

The impact of benthic macrofauna for nutrient fluxes from Baltic Sea sediments

This article focuses on the ecological role of benthic macrofauna on nutrient dynamics and benthic-pelagic coupling in the Baltic Sea with relation to eutrophication. Generally, benthic macrofaunal activities have large effects on sediment biogeochemistry and often with stimulatory effects on processes that counteract eutrophication, i.e., denitrification and increased phosphorus retention of the sediment. The degree of faunal impact on such processes varies depending on faunal density and functional group composition. The effect of macrofaunal activities on sediment nutrient dynamics can also result in a higher nitrogen: phosporus ratio of the sediments efflux compared with sediments without macrofauna. Increased internal nutrient loading during eutrophication-induced anoxia is suggested to be caused both by altered sediment biogeochemical processes and through reduced or lost bioturbating macrofauna and thereby a reduced stimulatory effect from their activities on natural purification processes of the Baltic Sea ecosystem.

Modeling the Baltic Sea eutrophication in a decision support system

SANBALTS (Simple As Necessary Baltic Long-Term Large-Scale) is a model of the coupled nitrogen and phosphorus cycles. This model has been developed as an integral part of the decision support system Marine Research on Eutrophication's Nest with the overall aim to evaluate management options for reducing Baltic Sea eutrophication. Simulated nutrient and oxygen concentrations as well as transport flows and major biogeochemical fluxes can be analyzed in many different ways, including construction of detailed nutrient budgets and tracing the fate of nutrient inputs. The large amounts of data that exist for this sea makes it possible to validate model results with observations. Major biogeochemical properties of the Baltic Sea are discussed through an analyses of model sensitivity to external forcing and internal parameterizations. Model results emphasize two features that are especially important for ecosystem management: i) impacts of local measures would always be modified by the long-range transports from other regions and ii) the response to significant changes in loads would only be seen after several decades.