Scientists call depletion of water oxygen a global threat

Scientists have warned that dissolved oxygen in oceans, lakes and rivers is declining at an alarming rate due to human activity, threatening water systems and the wider biosphere. A study published in Limnology and Oceanography urged that "water oxygen depletion" be included in the planetary boundaries framework, first developed in 2009 by 28 scientists to define nine vital Earth processes. Lead author Erica Ferrer of the University of California said planetary health depends on the health of water systems that require oxygen to function, and that water oxygen loss should be treated as a global issue rather than considered in isolation from other threats. The study identified two main drivers: warming tied to greenhouse gas emissions, which raises water temperatures and reduces oxygen-carrying capacity, and excess nitrogen and phosphorus from agriculture, sewage and industry, which fuels algal blooms that consume dissolved oxygen. Researchers said the world's oceans have lost roughly 2 percent of their dissolved oxygen since the 1950s, with Copernicus data projecting an additional 1 to 7 percent decline by the end of the century. The team proposed four indicators: dissolved oxygen concentration, the prevalence of low-oxygen zones, water's proximity to oxygen saturation and changes in oxygen-sensitive species. Including water oxygen depletion in the planetary boundaries framework is intended to draw global attention to the crisis and help guide a roadmap for solutions, according to the authors.