Abstract
Effects of nutrients released from suspended solids (SS) discharged by urban runoff on eutrophication in enclosed water body is not well known. In order to estimate the effects, amounts of nitrogen (N) and phosphorus (P) released from SS with decomposition were measured. Bottom sediment and periphyton in an urban river and sediment on road were collected from urban area as postulated SS discharged by urban runoff. The amounts of N and P released from SS measured by the repeated batch experiment were larger than those measured by batch experiment. This result showed adsorption and desorption equilibrium of nutrients between SS and ambient water was important for estimating the amounts of N and P released from SS. The amounts of released N and P were related to the initial amount of organic matter in SS. The percentage of released amounts to initial amounts of N and P in SS were rather small : 5-30% for N and 0-40% for P in 30 days. This result showed nutrients loads expressed by T-N and T-P parameters would be overestimated from the viewpoint of nutrients availability. Characterization of extractable P in SS before and after decomposition experiment showed that the fraction of organic P was released easier than the fractions of inorganic P, e.g., Fe-P and Al-P.
