Often neglected in global analyses, these ecosystems play a key role in biochemical cycling (Downing et al. 2009) and harbor about 6 percent of the global diversity (Dudgeon et al. 2006). Although a scarce commodity – only 1.49% of all the available water resources is stored in lakes and reservoirs - lake ecosystems provide important services to mankind, including recreational use, aquaculture, water for irrigation and drinking water, and habitat for rare species. Therefore, safe, good quality, and aesthetically acceptable water is a critical need on a worldwide scale.
Eutrophication is considered the most important water quality problem in freshwaters and coastal waters worldwide. In most fresh waters, phosphorus (P) is the main nutrient limiting primary production, and one of the key consequences of the high P loadings associated with eutrophication is the blooming of phytoplankton species, mainly cyanobacteria that may proliferate to very high densities and even accumulate at the water surface and lee-side shores in thick scums.
Extensive efforts to reduce the nutrient inputs to lake ecosystems and ecosystem restructuring have in many cases not resulted in expected clearing up of lakes from turbid, cyanobacteria dominated water to clear waters. Recent insights reveal that this recovery may take decades to centuries. The prime cause for hampered/delayed recovery is a bottom anoxia induced internal loading of phosphorus (P) released from a sediment pool, which was created when external loading was high and/or ongoing diffuse P inflow through groundwater. In my lecture I will talk about this phosphorus legacy and how we could mitigate present and future water quality problems