Spatial characters of nutrients in Wujiangdu Reservoir in karst river,SW China

A preliminary assessment of the Wujiangdu Reservoir examined nutrient distribution and transport.Water samples were collected in the summer(July) of 2004, during the high-flow season. Inorganic nutrients(N,P, Si) and chlorophyll a(chl a) concentrations of the Wujiangdu Reservoir and its inflow rivers were analyzed.Other water parameters(dissolved oxygen, p H, temperature, and electrical conductivity) were measured as well.The results show gradually decreasing concentrations of NO_3~--N and dissolved silicate in the surface water moving downstream to the dam of the Wujiangdu Reservoir.Additionally, soluble reactive phosphorus concentrations measured very low, with most falling below the sensitivity threshold of the method used in surface waters. Particulate phosphorus and NO_3~--N were the predominant species of phosphorus and nitrogen in the reservoir, respectively. The concentration of nutrients in the Yeji River was the largest of all inflow rivers. The maximum concentration of chl a was found near the dam. These results reflect upstream conditions similar to that of a river, and reservoir conditions near the dam similar to that of a natural lake system.