Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll-a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics

Water quality monitoring at Loch Leven 2008-2010: report of results

Long-term monitoring of the water quality in Loch Leven has been undertaken by the Natural Environment Research Council since the late 1960s. Over this period, the lake has suffered serious degradation due to the combined effects of eutrophication, pesticide pollution and climate change. However, following management intervention aimed at improving the water quality of the lake, the site has undergone a slow recovery. The recovery trajectory has, at times, seemed somewhat erratic. This is due to inter-annual variations in the in-lake processes that regulate the release of legacy phosphorus from the sediments following a reduction in catchment sources, although climatic variation and changes in biological interactions have also affected the recovery in the loch. This report summarises the findings of 40 years of research on Loch Leven and presents additional data from samples collected between 2008 and 2010. The more recent data are integrated into the longer term perspective to provide an indication of whether the recovery of Loch Leven is continuing. The implications of the findings from the Loch Leven Long Term Monitoring Project, in terms of achieving water quality targets and providing key ecosystem services, are discussed

Phosphorus partitioning in a shallow lake: implications for water quality management

This paper describes the seasonal partitioning of phosphorus (P) across the sediment–water interface in Loch Leven, Scotland, and discusses the implications for future lake management strategy with respect to recovery from eutrophication. In a 10-month survey, surface water total phosphorus (TP) concentrations were highest in late summer and lowest in early spring. In contrast, sediment TP concentrations were highest in mid-winter and lowest in late summer. Water discharge at the main outflow of the loch was highest when water-column TP was low and sediment TP high, and vice versa. Monthly sediment P uptake/release values showed significant cycling between the water-column and the sediment and showed seasonal variation in four release-sensitive P pools. Regulating the water level to increase flushing during sediment release periods and decrease flushing during uptake periods has the potential to significantly enhance the recovery of shallow lakes and reservoirs following historic nutrient loading