THE EFFECT OF RESERVOIRS ON PHOSPHORUS CONCENTRATION

The annual average degree of phosphorus retention (both TP and OF) in reservoirs was found to depend mainly on the theoretical retention tim e (RT). The phosphorus retention (RP) is shown for some reservoirs in Czech Republic to be well approximated (standard deviation = 10.9) wit h RP((TP))= 74.7 (1-exp(-0.0255* RT)) (N = 38, 7 less than or equal t o RT less than or equal to 604 days). The inclusion of 13 additional r eservoirs for which data were assembled from literature resulted in an almost identical relationship: RP((TP)) = 76.1 (1-exp(-0.0282* RT)) (N = 51, range of RT nearly unchanged). The retention of soluble react ive phosphorus RP((OP)) studied on data from literature seems to be hi gher than that of TP. Statistical comparison with data for RP(TP) of l akes has shown a significantly lower retention in lakes than in reserv oirs for comparable RP, resulting in RP((TP)) = 66.0 (1-exp(-0.00419* RT)) (N = 59, 5.8 less than or equal to RT less than or equal to 260 000 days). The differences between RP((OP)), and RP((TP)) and differen tiation of lakes and reservoirs are discussed and a need for more thor ough theoretical analysis stressed. Consequences for watershed managem ent are summarized.