Researchers say global warming is reducing oxygen levels in lakes

Researchers published a new study that found oxygen levels in the temperate freshwater lakes worldwide are declining faster than in the oceans. Scientists say that the trend is driven mainly by climate change and threatens freshwater biodiversity and the quality of drinking water. Oxygen levels in lakes across the temperate zone have declined 5.5 percent on the surface and 18.6 percent in deeper water since 1980.

When investigating a large subset of mostly nutrient-polluted lakes, surface oxygen levels increased as water temperature crossed a threshold favoring cyanobacteria which create toxins in the form of harmful algal blooms. Researcher Kevin Rose from the Rensselaer Polytechnic Institute says since all complex life needs oxygen, the oxygen is the support system for aquatic food webs. If lakes begin to lose oxygen, there is the potential that species could be lost.

Rose says lakes are losing oxygen between 2.75 and 9.3 times faster than the ocean. The decline of oxygen could have an impact on the ecosystem. In the study, researchers analyzed over 45,000 dissolved oxygen and temperature profiles created since 1941 from about 400 lakes globally. Most of the long-term records were collected in the temperate zone from 23 to 66 degrees north and south latitude.

The concentration of dissolved oxygen in aquatic ecosystems impacts greenhouse gas emissions, nutrient biochemistry, and human health. Lakes make up only about three percent of the earth's land surface but contain a significant concentration of the planet's biodiversity. Lead study author Stephen F. Jane said that lakes are indicators of environmental change and potential threats to the environment because they respond to signals from the surrounding landscape and atmosphere.

The deoxygenation of surface water was driven by physics. According to the study, surface water temperatures increased by .38 degrees centigrade per decade, and surface water dissolved oxygen concentration declined by .11 milligrams per liter per decade. Researchers say that some lakes that experienced increasing dissolved oxygen concentrations and warming temperatures were more polluted with nutrient-rich runoff from agricultural and developed watersheds, which favor cyanobacteria blooms.