NUTRIENT REMOVAL CAPACITY IN SUBMERSED MACROPHYTE POND SYSTEMS IN A TEMPERATE CLIMATE

The natural capacity of submersed plants to reduce the phosphorus and nitrogen content of polluted waters was investigated in a full-scale experiment with Elodea canadensis and Cladophora glomerata, grown in eutrophied stream water in 16 parallel canals in Southern Sweden. Between September 1988 and June 1991 the weekly mean reduction was 32% of nitrogen and 62% of phosphorus, equivalent to specific mean reductions of 0.5 g N M-2 d-1 and 0.04 g P m-2 d-1. Harvested biomass contained approximately 10% of removed nitrogen and 20% of removed phosphorus. Sediment nutrient content and regression analysis showing that nitrogen removal was strongly dependent on temperature and nitrogen load suggest that denitrification was the major nitrogen removal process. Sediment burial was the most important phosphorus removal mechanism. Variations in phosphorus removal were largely explained by insolation, supporting the hypothesis that biomass uptake is important for phosphorus removal. Both nitrogen and phosphorus removal were correlated to detention time.