Sediment resuspension and denitrification affect the nitrogen to phosphorus ratio of shallow lake waters

摘要

The effect of sediment resuspension on the nitrogen to phosphorus (N:P) ratio of lake water as well as on concentrations of total and dissolved nitrogen and phosphorus were studied experimentally in shallow eutrophic Lake Kirkkoj?rvi. In addition the denitrification rate and potential were measured, using the isotope-pairing technique concomitantly with the resuspension experiments. Resuspension increased the concentration of total phosphorus (TP) relatively more than the concentration of total nitrogen (TN), thus decreasing the TN to TP ratio, regardless of the phase of the growing season. Resuspension also had various effects on the dissolved nitrogen and phosphorus concentrations. The denitrification rate was highest in May, when the supply of nitrate was high. In August, when the denitrification potential peaked due to high temperature, the low availability of nitrate limited nitrogen removal. However, sedimentary denitrification during the open-water season was so intense that it also lowered the N:P ratio in the water directly and not only by lowering the ratio in the sediment prone to resuspension.