Long-term trends in eutrophication and nutrients in the coastal zone

We used high-resolution paleoecological records of environmental change to study the rate and magnitude of eutrophication over the last century in two contrasting coastal ecosystems. A multiproxy approach using geochemical and biological indicators and diatom-based transfer functions provides a long-term perspective on changes in nutrient concentrations and the corresponding biological and sedimentary responses. In Roskilde Fjord, Denmark, total nitrogen (TN) increased 85% during the last century, with the most rapid increase occurring after the 1950s, corresponding to the postwar increase in N fertilizer use. In LaaJalahti Bay, an urban embayment near Helsinki, Finland, total dissolved nitrogen (TDN) increased with growing wastewater inputs and decreased with the remedial actions taken to reduce these discharges. These changes are small relative to the order of magnitude increases in nutrient loading that have occurred in northwestern Europe, where the dissolved inorganic nitrogen (DIN) load has increased more than threefold in certain areas.