The rates of dry matter and nutrient loss from decomposing Potamogeton pectinatus in a brackish south-temperate coastal lake

SUMMARY. Decomposition of Potamogeton pectinatus in Swartvlei, a southern African coastal lake, followed an exponential pattern of decay. The rale constant was 0.0205 day⁻¹ and decay was virtually complete after 158 days. The original stock of ash, phosphorus and potassium was lost more rapidly than dry matter in the initial stages of decomposition due to leaching. Almost the entire stock of potassium and 60% of the phosphorus was lost in the first 7 days. The proportions of N and P in the decomposing detritus increase significantly in the final stages of decomposition, providing a rich food source for the abundant filter-feeding animals of the littoral zone. The decomposition rate of P. pectinatus is compared with that of other aquatic macrophytes and the significance of the relatively rapid decay rate of this species in the ecology of Swartvlei lake is discussed.