Time scales of nutrient losses from land to sea - a European perspective

Empirical data regarding the time scales of nutrient losses from soil to wa ter and land to sea were reviewed. The appearance of strongly elevated conc entrations of nitrogen and phosphorus in major European rivers was found to be primarily a post-war phenomenon. However. the relatively rapid water qu ality response to increased point source emissions and intensified agricult ure does not imply that the reaction to decreased emissions will be equally rapid. Long-term fertilisation experiments have shown that important proce sses in the large-scale turnover of nitrogen operate on a time scale of dec ades up to at least a century, and in several major Eastern European rivers there is a remarkable lack of response to the dramatic decrease in the use of commercial fertilisers that started in the late 1980s. In Western Europ e, studies of decreased phosphorus emissions have shown that riverine loads of this element can be rapidly reduced from high to moderate levels, where as a further reduction, if achieved at all, may take decades. Together, the reviewed studies showed that the inertia of the systems that control the l oss of nutrients from land to sea was underestimated when the present goal of a 50% reduction of the input of nutrients to the Baltic Sea and the Nort h Sea was adopted. (C) 2000 Elsevier Science B.V. All rights reserved.