Emergent patterns in nature and society

Extreme cold event collapse fishery and induce hypoxia in Bolivia rivers

Last week, the World Water Week was held in Stockholm. According with Swedish newspapers, one of the issues more debated was increasing variability of rainfall in the northern hemisphere summer, which lead to sounded headlines related to fires in Russia and floods in Pakistan.

However, the southern hemisphere was no the exception, in such case suffering of extreme events presumably due to climate change. NatureNews reports that the unprecedented wave of cold in Bolivia killed at least 6 million fish and thousands of other animals related with riverine ecosystems. They add the following on the ecosystem services affected:

The extraordinary quantity of decomposing fish flesh has polluted the waters of the Grande, Pirai and Ichilo rivers to the extent that local authorities have had to provide alternative sources of drinking water for towns along the rivers’ banks. Many fishermen have lost their main source of income, having been banned from removing any more fish from populations that will probably struggle to recover.

The blame lies, at least indirectly, with a mass of Antarctic air that settled over the Southern Cone of South America for most of July. The prolonged cold snap has also been linked to the deaths of at least 550 penguins along the coasts of Brazil and thousands of cattle in Paraguay and Brazil, as well as hundreds of people in the region.

Water temperatures in Bolivian rivers that normally register about 15 ˚C during the day fell to as low as 4 ˚C.

The causes, however, remain unknown and open an active front for South America research. Interestingly, among the causes proposed there is a feedback mechanism related with hypoxia; given that the cold temperature can reduce water mixing, causing in turn lower oxygen levels. Other interactive drivers proposed are disease outbreaks and pollution.

via: Cold empties Bolivian rivers of fish : Nature News.

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