Response to lowered nutrient discharges in the coastal waters around the island of Funen, Denmark

The Danish Action Plan for the Aquatic Environment of 1987 prescribes a 50% and 80% run-off reduction of nitrogen and phosphorus, respectively, to the aquatic environment. This is meant to reduce the seriously increasing eutrophication problems, such as widespread hypoxia and anoxia, in the coastal regions of Denmark. In spite of major investments in sewage treatment, these objectives have generally not been realised, primarily because of lack of substantial reductions in nitrogen run-off from diffuse agricultural sources. On the island of Funen, Denmark, precipitation in the last two years has been extremely low, leading to major decrease in nitrogen and phosphorus run-off to the surrounding coastal waters. For primarily meteorological reasons, the objectives of the Action Plan were thus fulfilled for the first time. Immediate response was registered in the coastal waters around Funen: very low nutrient concentrations during winter 1995/96, higher Secchi depths, lower phytoplankton production and biomass, increasing depth distribution of eelgrass (Zostera marina) and higher oxygen concentration in bottom-near water in spring and summer 1996 compared to previous years. This natural 'experiment' suggests that substantially lower nutrient loads to coastal marine systems can have an immediate, positive impact on oxygen conditions in bottom-near waters.[PUBLICATION ABSTRACT]