The nutrient budget of a small eutrophic loch and the effectiveness of straw bales in controlling algal blooms

1. A 1-year intensive study of nutrient flows in Airthrey Loch, central Scotland, a small eutrophic mean total phosphorus (TP) = 61.1 μg P l^–1] well-flushed freshwater body (area, 6.9 ha; mean depth, 1.85 m; volume, 1.274 × 10⁵ m³; retention time, 0.44 yr), was undertaken.
2. The nutrient budget was dominated by large allochthonous P inputs, equivalent to an areal load to the loch of 8.56 kg P ha^–1 yr^–1, which occurred predominantly during winter. In the summer, when TP inputs were low, water column levels of TP still increased, as a result of aerobic P release from sediments.
3. Sorption experiments indicated potential for sediment P release at water P concentrations of up to 200 μg P l^–1.
4. Aerobic release rate of P from sediments to the water column of Airthrey Loch was estimated to be of the order of 1 mg P m^–2 day^–1, and occurred during periods of elevated water column pH.
5. Straw bales placed in the loch to retard algal blooms were found not to have any demonstrable impact on algal concentrations observed during the study.