Modeling the effects of macrophyte growth and decomposition on the nutrient budget in Shallow Lakes

A numerical model was developed to illustrate the annual life cycle and the decomposition process of Potamogeton pectinatus L. Growth, decay, and thei r interactions were considered simultaneously for five fractions: main and secondary shoots, roots, tubers, and new tubers. The model was applied to f ield experiments carried out in Swartvlei Lake (South Africa). The predicti ons of the model for biomass of each fraction, standing stock of phosphorus and phosphorus content in shoots, secondary shoots and roots well agree wi th the observed values. The model successfully simulated the decomposition process, the remaining dry mass, and the phosphorus and nitrogen content of the remaining biomass. A series of numerical experiments were subsequently carried out to investigate the long-term effects of macrophyte decompositi on on the nutrient budget of a hypothetical lake. Results show that phospho rus released in the decomposition process of macrophytes in the lake can be reduced significantly, at least by 75%, if the above-ground macrophyte bio mass is harvested at the end of the growing season. Moreover, phosphate lea ched to the overlying water can be reduced to less than half within 10 year s, if the above-ground biomass (AGB) is removed. (C) 2000 Elsevier Science B.V. All rights reserved.