Partial photo: Leon Ephraim
Rivers and streams are a large source of greenhouse gases with water pollution making their emissions much worse. They release up to 3.9 billion tons of carbon each year (around four times that emitted annually by the global aviation industry). Aquatic systems contribute more than 50% to atmospheric methane, and global river N2O emissions exceed 10% of human emissions. The increase of river emissions is highly correlated to changes in land use and land cover. Average CO2 and N2O concentrations of sites close to urban areas were around four times higher than those of natural sites with this ratio 25 times in case of methane. After entering freshwater bodies, pollution from human activity and nitrogen are converted to greenhouse gases by microorganisms. When dissolved oxygen drops because of pollution, anaerobic bacteria mineralise organic matter to produce CO2 and methane while denitrifying bacteria converts nitrate to nitrous oxide. Increased urbanization has introduced numerous contaminants to rivers as more than 80% of municipal wastewater is directly discharged into the environment. Most pollutants come from untreated wastewater, agricultural runoffs, and increased sediment accumulation. The solutions are obvious.
www.bbc.com/future/article/20210323-climate-change-the-rivers-that-breathe-greenhouse-gases