| For many, lakes are not only an iconic symbol of Sweden’s natural beauty, they are also used for fishing, recreational opportunities, and other aesthetic pleasures. Unfortunately human development has degraded many lakes via excess nutrient inputs (eutrophication). Considerable efforts have been made to reduce external phosphorus (P) sources to lakes, but internal loading due to historical accumulation of P in lake sediments can delay recovery by up to a century or more. As the Water Framework Directive (WFD) requires all lakes to reach good ecological status by 2020, great efforts are needed to manage internal P loading in lakes so they meet both WFD and Swedish water quality goals.
This project focuses on one of the most common restoration options: sediment P inactivation using P-binding agents (metals and clays). While binding of P by metals and clays is an on-going natural process in lake sediments, binding capacity is often overwhelmed by excessive external P inputs and thus more binding material is needed to restore balance. There are two factors, however, that limit treatment effectiveness: sediment disturbance by bottom feeding fish and excess organic sediment P. Because we lack knowledge with respect to these issues, we have developed a project to answer the following questions:
How can dosing methods be improved to effectively bind organic P as it degrades over time?
How does sediment disturbance by benthic fish alter internal P loading and the effectiveness of sediment inactivation?
Are newly developed, engineered clays a cost effective alternative to metals for controlling internal P loading under varying sediment and mixing conditions?
To answer the above questions, a combination of lab and field studies will be employed. To study the relationship between organic P and binding agent over time, binding agent (aluminium and clay) will be added to sediment under different scenarios that will test the effectiveness for binding organic P. The results will be used to improve the dosing method so that this P fraction can be effectively controlled. Constructed ponds and tanks (Drottningholm) will be used to study the effect benthic fish have on sediment mixing and P release. Although we know that benthic feeding fish disturb sediment while feeding, there is no information on how this affects sediment P cycling from the sediment. The pond study will determine changes in sediment mixing depth and P cycling and constructed tanks will be used to determine the effect of sediment mixing on the ability of both aluminium and clay to bind with P under these conditions.
The results from both the laboratory and field studies will also provide knowledge on the relative costs and potential effectiveness of these two P-binding agents so that an informed assessment can be made by lake managers as to which method is the most cost-effective for lake management and restoration. This project is also directly related to the objectives of Stiftelse Oscar och Lili Lamms minne with respect to conservation of natural and water resources. |