Epilithic and planktonic leucine aminopeptidase activity and leucine assimilation along the River Tweed, Scottish Borders

The microbial organic-nitrogen transformation variables, extracellular leuc ine aminopeptidase activity, and leucine assimilation, were determined at s tone surfaces and in river water at six sites along 138 km of the River Twe ed and also in a major tributary, the River Teviot. Sampling was on 3 days, representative of spring, summer and autumn. The variables, except for epi lithic leucine assimilation, all showed significant downstream increase on at least 2 of the sampling days. Their values tended to be lowest in spring (early April). Aminopeptidase activity, leucine assimilation, microbial ab undance, and pattern of downstream increase in the Tweed were shown to be b roadly similar to in the River Swale, northern England. Microbial organic-n itrogen transformations and abundance in the Teviot tended to equal or exce ed those in the lower Tweed, probably because of enrichment of the tributar y by sewage-works discharges. (C) 2000 Elsevier Science B.V. All rights res erved.