TRENDS IN NUTRIENTS

The roles of nitrogen (N) and phosphorus (P) as key nutrients determin ing the trophic status of water bodies are examined, and evidence revi ewed for trends in concentrations of N and P species which occur in fr eshwaters, primarily in northern temperate environments, Data are repo rted for water bodies undergoing eutrophication and acidification, esp ecially water bodies receiving increased nitrogen inputs through the a tmospheric deposition of nitrogen oxides (NOx). Nutrient loading on gr oundwaters and surface freshwaters is assessed with respect to causes and rates of change, relative rates of change for N and P, and implica tions of change for the future management of lakes, rivers and groundw aters. In particular, the nature and emphasis of studies for N species and P fractions in lakes versus rivers and groundwaters are contraste d. This review paper primarily focuses on results from North America a nd Europe, particularly for the UK where a wide range of data sets exi sts. Few nutrient loading data have been published on water bodies in less developed countries; however, some of the available data are pres ented to provide a global perspective. In general, N and P concentrati ons have increased dramatically (>20 times background concentrations) in many areas and causes vary considerably, ranging from urbanization to changes in agricultural practices.