The work was published on December 6 in the journal Global Change Biology.
“There are significantly more lakes with dissolved oxygen loss than those with upwelling,” said the lead researcher Stephen Jane, PhD researcher at the Cornell Atkinson Center for Sustainability. “On a large scale, aerobic organisms will lose available habitat as lakes continue to warm. This is especially true for organisms that survive warm periods in the cool waters of deep lakes.”
Jane and her colleagues examined about 25 years of available data from more than 400 lakes — mostly in the United States — to identify the loss of dissolved oxygen. In addition to Rondaxe Lake, the team studied New York’s Neversink (Sullivan County) and Cannonsville (Delaware County) reservoirs, as well as Jockeybush and Sagamore lakes (Hamilton County).
In temperate lakes, the researchers found that the amount of low-oxygen water increases by an average of 0.9-1.7 percent per decade and found that the amount of oxygen-deficient lake water has increased by more than 50 percent since three decades ago.
Reducing oxygen in lake water can have many effects. For example, methane – a powerful greenhouse gas – may accumulate in oxygen-free parts of the water column. Nutrients, such as phosphorus from agricultural fertilizers, released from unsettled lake sediments can enter the water column, increasing the likelihood of harmful algal blooms.
In a typical July-August, the surface of the lake can be around 70 degrees, while the bottom of the lake can be around 40 degrees. “Water temperature and density are related,” Jane said. “So it becomes a situation where you basically have oil and vinegar, where the strong water temperature differences between the layers create a resistance to mixing — which is stratification.”
The result is that atmospheric oxygen is prevented from replenishing dissolved oxygen in deep waters, Jane said. As winter ends earlier than decades ago, seasonal stratification begins earlier and ends later.
These stratification changes result in deep-sea habitats having more time to deoxygenate – an interruption of the natural oxygenation process.
“We show here that as warming continues, the depositional time of lakes increases and this leads to an increase in the amount of low-oxygen water in the lakes,” said the second author. Kevin Rose, assistant professor at Rensselaer Polytechnic Institute, Troy, New York. “The bad news is that given projected warming rates, the amount of oxygen-depleted water in lakes is likely to increase even more in the future.”
HT
Source: ANI
Source: The Nordic Page