CONCENTRATIONS AND DISTRIBUTIONS OF NITROGEN AND PHOSPHORUS IN SEDIMENT AND INTERSTITIAL WATER OF LAKE DONGHU IN WUHAN

This paper summarizes the concentrations of nitrogen and phosphorus and their distributions in the sediment and interstitial water in Lake Donghu during the period from October 1982 to July 1984. The mean concentrations of nitrogen (N) and phosphorus (P), in the sediment were 14.2 mg/g and 0.87 mg/g (d.w.) respectively, in the upper layer (0—10 cm), 12.2 mg/g and 0.62 mg/g (d. w.) in the lower layer (10—40 cm). Concentrations of nitrogen and phosphorus in the sediment varied greatly in both vertical and horizontal distributions. In all sampling stations, the concentrations of the mentioned substances at station Ⅰ were the highest; the concentrations in the upper layer were higher than those in the lower layer as well.The concentration of total dissolved nitrogen (TDN) in the interstitial water of superficial sediments was high, being 11.52 rag/l in average. TDN existed mainly in the form of ammonic nitrogen, which amounted to 61.3% of the total. The concentration of total dissolved phosphorus (TDP) in the interstitial water of sediments was low, being 0.113 mg/l, of which 55.8% was orthophosphate. There were marked seasonal variations in the concentrations of nitrogen and phosphorus in the interstitial water, and the higher concentrations were observed in summer and autumn and while the lower ones, in winter and spring. Except for ammonium nitrogen, concentrations of nitrogen and phosphorus in interstitial water were generally within the range of five times higher than those in the mud. Thus, there is an intensive nutrient exchange between sediment and water in the lake.