The data on nitrogen and phosphorus fractions obtained during the core study programme of the Land Ocean Interaction Study for rivers draining the central part of eastern UK are presented and assessed with respect to sources and potential biological effects. The approaches used include comparisons of: (1) overall speciation of nitrogen and phosphorus in the rivers by examining average values and ranges; (2) relationships between nitrogen and phosphorus fractions and flow; and (3) relationships between nitrate and total dissolved nitrogen and soluble reactive phosphorus and total dissolved phosphorus. In addition, comparisons are made between data from the LOIS study region and literature on rivers elsewhere in Europe and North America. Detailed consideration is given to N/P mass ratios in river water, because these can indicate conditions of potential N- or P-limitation for algal and other plant growth. A mid-river site in the Ure, a tributary of Yorkshire Ouse, showed 44% of samples with a N/P mass ratio of > 24. Comparison of records for the 'growing season' (April to September), when algal and other plant activity is highest, with those from the 'dormant season' (October to March) showed a much higher N/P mass ratio during the growing season, indicating that conspicuous growths of Cladophora glomerata and other submerged plants may be reducing ambient phosphate to levels of marked phosphorus limitation. (C) 1998 Elsevier Science B.V.
