GROWTH AND NUTRIENT-UPTAKE BY 2 SPECIES OF ELODEA IN EXPERIMENTAL CONDITIONS AND THEIR ROLE IN NUTRIENT ACCUMULATION IN A MACROPHYTE-DOMINATED LAKE

The capacity of Elodea nuttallii(Planch.) St. John and Elodea canadensis Michx. to remove nitrogen from water was evaluated in laboratory experiment. The growth rate of plants and their effect on the nitrogen level of hypertrophic Lake Zwemlust (the Netherlands) as well as on lake water enriched with nitrogen were investigated. The plants grew best in water enriched with up to 2 mg NH4-N l-1 and 2 mg NH4-N l-1 plus 2 mg NO3-N l-1. During a 14 day experiment, plants absorbed from 75% to 90% of nitrogen. Higher nitrogen concentration than 4 mg l-1 had a negative effect on growth of both species. Elodea nuttallii and E. canadensis prefer NO4+ over NO when both ions were present in water in equal concentrations.