Phosphorus in lakes - Eutrophication indicators in lakes

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During the past few decades there has been a gradual reduction in phosphorus concentrations in many European lakes. Discharges of urban wastewater have been a major source of pollution by phosphorus, but as purification has improved and many outlets have been diverted away from lakes, this source of pollution is gradually becoming less important. Agricultural sources, both from animal manure and from diffuse pollution by erosion and leaching are similarly important and need attention to obtain good water quality in the lakes. The improvements have generally been relatively slow despite the pollution abatement measures taken. This is at least partly because of the slow recovery due to internal loading and because the ecosystems can be resistant to improvement and thereby maintain a bad steady state. Particularly in shallow lakes, such problems may call for restoration measures.