Ancient blue‐green blooms

Recent decades have seen a large increase in surface scums (blooms) of cyanophytes (blue‐green algae and blue‐green bacteria) in inland waters. These are potentially toxic to mammals, including humans, and have caused considerable public concern in Europe, Australasia, and North America. They are often associated with eutrophication, and much has been invested in their control. Not all blooms, however, are necessarily the results of human interference with lakes. Scattered paleolimnological evidence indicates that some blooms may be associated with pristine conditions, though this message has largely been ignored. Evidence is given here of a long history of blooms in Whitemere, U.K., from extraction and identification of specific carotenoids from dated sediment cores. Whitemere is representative of a large group of lakes in the West Midlands of the U.K. and is likely to be representative also of those similar postglacial kettle hole lakes in North America and Eurasia, which are groundwater fed with long retention times and thermally stratified. Blue‐green blooms may thus be a normal feature of such lakes and not necessarily a pathology to be controlled.

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