REDUCING NUTRIENT RELEASE FROM SEDIMENTS: ECOLOGICAL RISKS

摘要

The application of active barrier materials, such as calcite, clays and zeolites, to lake sediments is being trialled in a number of countries as a low-cost method for preventing phosphorus release for sediments, and therefore reducing the risks of algal blooms. Laboratory work has shown that precipitated forms of calcite (CaCO_3) are effective in reducing phosphorus release from anaerobic sediments in Lake Carramar, a small urban lake in Melbourne. A three-stage protocol for assessing the ecological risks associated with the possible application of an active barrier has been developed and applied to Lake Carramar. Four possible ecological issues were identified and these were subjected to a qualitative ecological risk assessment. There was a high risk that a calcite layer would adversely affect the benthic algae growing on the bottom sediments of Lake Carramar, although there is a lack of information to assess the magnitude of this effect. There is also a moderate likelihood that a calcite barrier would reduce the levels of other phytoplankton (in addition to the targeted cyanobacteria), resulting in major implications for the zooplankton population, which depend upon the phytoplankton for food, and for the fish population that in turn depends upon the zooplankton. This poses a high risk to the overall ecological health of the lake. The other two issues - toxicity of the barrier material and turbidity increases due to the application of the material with possible impact on light penetration and phytoplankton production - were rated as low risk.