Nutrient relationships in shallow water in an African Lake, Lake Naivasha.

In the littoral zone of a shallow, tropical lake (Lake Naivasha, Kenya), average nutrient composition of emergent macrophytes along a permanent transect (0-2m depth) on a dry weight basis was: P 0.23%; N 0.96%; and S 0.11%. In the hydrosoil the average composition was much lower, sediments were: P 0.03%; N 0.24%; and S 0.05%. The water depth varied, with lake edge being exposed during the annual drawdown for a part of the year and subsequently being inundated. Water quality varied considerably during the year (temperature 19-28°C; pH 7.0-8.0; conductivity 282-975 μ Scm-1).Of the three nutrients in the water of the littoral zone, N had the highest mean concentration (4.25 mg·1-1) while P was intermediate (1.90) and sulphur had the least (0.99). The distribution of nutrients followed a decreasing gradient from shore to open water. High levels of nutrients were recorded in September following the inundation of drawdown soil and plant material.The large stock of nutrients generated in the littoral zone helps to replenish nutrients in the open lake where low concentrations are typical.