Eutrophication is commonly seen as a modern problem, resulting from increased use of natural and organic fertilisers and runoff into freshwater systems. The nutrient enrichment of the waters results in planktonic blooms, cutting off sunlight supply and depleting resources in the water for bottom-dwelling animals.
However, evidence from the fossil records suggests that eutrophication has been a problem throughout history, long before humans were in the picture. The Devonian period saw the rise of the vascular plants and subsequent creation of rich soils on the land. Soil formation and rooting of vascular plants into the bedrock promotes chemical weathering, and the sudden influx of ions into water systems may have resulted in algal blooms on a phenomenal scale. The changes in global biogeochemical cycles (of carbon, phosphorous and nitrogen) could then have caused the end-Devonian extinction by way of global cooling (as a result of increased carbon burial) and marine anoxia, where 50% of all genera became extinct.
Unfortunately, eutrophication is expected to increase over the 21st century, which will put many freshwater and marine ecosystems at risk, in fact there have been proposed threshold levels of annual nitrogen and phosphorus influx into freshwater ecosystems to prevent widespread eutrophication. However, ecosystems are known to bounce back from the effects of eutrophication when given the adequate treatment and time to recover such as that seen in Lake Constance. Although, the recovery here was only made possible by high levels of genetic diversity, which is not often the case in populations that have already been massively reduced, which is seen in systems affected by eutrophication.