Restoration of Eutrophic Lakes by Sediment Treatment

Abstract

Sediment treatment with nitrate as an oxidising agent has been used successfully on Lake Lillesjön in southern Sweden, smaller ponds near Berlin or at the Alte Donau, a eutrophicated dead-arm of the River Danube in Vienna. Specially-designed equipment has been used to inject nitrate solution directly into the sediment so as to minimise the risk of increasing the nitrogen concentration in the water. Iron salts are usually added to enhance the binding of phosphorus in the sediment. Reactions involved when such treatment is implemented are processes that normally occur naturally in lakes in the top sediment layers. However, with an excessive input of nutrients to a lake from its catchment, the natural process of phosphorus binding becomes insufficient; due to the oxygen depletion at the ­bottom of the lake, phosphorus is released from the sediment to the water, ­enhancing primary production and thus disturbing the balance between production and decomposition of organic matter. To prevent further degradation of the lake ecosystem, sediment treatment can be used.