Influence of benthic diatoms on the nutrient release from sediments of shallow lakes recovering from eutrophication

Measures taken to combat eutrophication resulted in a decrease in phytoplankton chlorophyll and an increase in transparency in the lakes studied. Because of the low nutrient concentrations in the overlying water, the increased light availability and the relatively nutrient rich sediments, a benthic algae community developed. In this study the interactions between the benthic algae and the nutrient release from the sediments is examined. In laboratory experiments it is demonstrated that benthic diatoms are able to grow on nutrients released from the sediments. The direct result is a decrease of the nutrient flux from the sediments by uptake by benthic diatoms. An indirect effect is an increased loss of nitrogen from the sediment water system to the atmosphere by stimulation of the coupled nitrification-denitrification. This is caused by an increased O₂ penetration depth due to the photosynthesis of benthic diatoms. Based upon these laboratory results and additional calculations, it is concluded that the benthic diatoms in the field are able to reduce the nutrient release from the sediments and thus the availability for the phytoplankton. The benthic diatoms therefore may accelerate the process of recovery from eutrophication.