An ecosystem management framework to maintain water quality in a macrophyte-dominated, productive, shallow reservoir

Loch Leven, SK, is a well-oxygenated, highly productive, clear-water lake dominated by a nuisance species of submergent macrophyte (Elodea canadensis Michaux) whose removal has been suggested to enhance recreational use. Previous empirical and theoretical work, however, has suggested that macrophytes offer an important ecosystem service in such lakes by sequestering nutrients, anchoring sediments, and providing shelter for filter feeding consumers. Macrophyte removal would introduce a risk of shifting the ecosystem to a less desirable turbid state, potentially dominated by toxic planktonic algal species. Here, we present the results of a contemporary (2014) spatio-temporal field survey of Loch Leven, which showed high water quality along several axes of assessment. Results are discussed within the context of historical sedimentary analysis, which indicated increases in algal biomass since 1980. Given the high potential for increases in planktonic biomass should Elodea be harvested, we propose only targeted macrophyte management for Loch Leven, and that large-scale Elodea removal programs would have to be paired with dredging of lake sediments to remove the source of internal nutrient loading. We further suggest that a long-term monitoring program be initiated to allow continued assessment of water quality in this shallow, macrophyte-dominated lake.