The hilltop fishing spot feeds into Dianchi Lake in south-western Yunnan province, a major tourist attraction and one of China’s largest fresh water bodies. Dianchi is famous for a number of reasons: its sheer size (nearly 40km long), its distinctive “crescent moon” shape and the surrounding scenic hills and rock gardens. But it has another distinguishing feature; for several decades, each summer the surface of Dianchi has turned bright green from algae blooms caused by excess nutrients such as nitrogen and phosphorus – a largely manmade phenomenon known as eutrophication.
Eutrophicationplagues areas around the world where rapid urbanisation and agricultural growth has taken place near bodies of water. When it rains, chemicals from cities, factories and fertilisers or untreated animal waste on farms can wash into lakes, streams and rivers. The extra nutrients feed algae on the surface of the water that can proliferate enough to block light. This deprives organisms of the light they need to photosynthesise. In the UK, for example, Tamar Lakes in south-western England suffered intense eutrophication pollution between 1975 and the 2000s, and the phenomena is also widespread in estuaries and coastal areas in the US.
Animal husbandry is a major contributor to contamination of China’s vital drinking water and seafood sources. The extensive survey of the impact of China’s agricultural transition published in Environmental Research Letters in 2016 found that in 2000, when the country was systematically expanding the size of farms, 30% to 70% of manure was dumped directly into rivers. Before 1970, when farms were mostly owned by single families, only 5% of manure was dumped into rivers. Later, a field test by Anhui Agricultural University showed that agricultural activity around Chaohu Lake in central Anhui province was the primary cause of pollution, according to a 2013 state newspaper report.
Read full article at The Guardian
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