Dynamics of dissolved nutrients among different macrophyte stands in a shallow lake

Abstract

Seasonally changing mechanisms affect the concentrations of dissolved inorganic nitrogen and soluble reactive phosphorus, which differ between the stands of different macrophyte life forms and open water in a eutrophic lake. Macrophytes that take nutrients up for their growth also shelter sediments from resuspension that brings nutrients back to the water and affect denitrification, which removes nitrogen from the water ecosystem. In this study the changes in nutrient concentrations were observed during the open-water period from April to November, and also denitrification rates were measured at different phases of the open-water season. The study was conducted at a shallow eutrophic lake where the effect of macrophytes on water quality is remarkable. The concentration changes of different nitrogen forms during the summer were very similar at the open-water and floating-leaved macrophyte (Nuphar lutea L.) stations. Nitrate was depleted faster among the submerged macrophytes (Myriophyllum verticillatum L.) than among floating-leaved plants or in open water. The decrease in the concentration of nitrate was so significant during the summer that it also affected the total nitrogen concentration in the water. Denitrification was highest in sediments among floating-leaved macrophytes (average 4.3 mg N m−2 d−1) and lowest in sediments of submerged plants (average 1.5 mg N m−2 d−1). Denitrification among submerged macrophytes was limited by low nitrate availability.