Reports of the damage we are doing to our planet come with a depressing regularity these days. Yet, they seem to be shrugged off with the same complacency and a there’s-nothing-we-can-do-about-it resignation as the latest mass shooting.
Earlier this month, a study was released that warns of far-reaching impacts for Minnesota, and the planet, without significant changes. In some ways, it is already too late to prevent the damage underway, but we can mitigate the depth and reach of that damage in the years to come.
In looking at close to 400 freshwater lakes in the U.S. and Europe, researchers found that many have seen reduced oxygen levels over the past 40 years, with potentially devastating consequences ahead for aquatic and human life. The loss of oxygen occurs both at the surface and in the deep, colder parts of the lake where some fish species move to survive the summer heat, their report says.
“Oxygen is one of the best indicators of ecosystem health, and changes in this study reflect a pronounced human footprint,” study co-author Craig E. Williamson, a biology professor at Miami University in Ohio, told Associated Press Science Writer Drew Costley.
Among the primary causes for falling oxygen levels are a warming planet, decreased water clarity due to pollution and sediment runoff, and expanding algae blooms.
“Surface water temperatures have risen by more than 7 degrees Fahrenheit on average over the past 40 years,” Greg Stanley of the Star Tribune writes. “Couple that with the excess nutrients that have crept into lakes from fertilizer runoff and urban development, and algae blooms can quickly take over the surface of a body of water.” Phosphorus and nitrogen runoff are the primary accelerators of algae blooms.
Algae blooms create dead zones as they decompose. Reduced oxygen levels are already leading to increased fish kills as they essentially slowly suffocate. Algae decomposing also increases the levels of methane emissions, pumping even more planet-warming gas into the atmosphere.
“Loss of oxygen in deep waters of lakes has a number of implications for biodiversity and ecosystem function, including a loss of habitat for organisms that require cold, oxygenated water (including cold-water fish such as cisco, whitefish, and lake trout).” Ultimately, the study says, humans will suffer the impacts of what is happening to our waters.
Researchers at the University of Minnesota and Rensselaer Polytechnic Institute in New York have found that “oxygen levels in the world’s temperate freshwater lakes are declining at rates faster than in the oceans.” Their work was published in the journal Nature recently.
“Previous research has documented global declines in oxygen of oceans, or focused on individual lakes, but this project is the first to document dramatic loss of oxygen in the deep waters of lakes around the world.” says co-author Gretchen Hansen, assistant professor of fisheries ecology at the U of M’s College of Food, Agricultural and Natural Resource Sciences.
“Minnesota is known for lakes with high water quality and these lakes contribute to local economies by supporting popular activities like fishing,” said Lesley Knoll, a freshwater ecologist and associate director at the University of Minnesota’s Itasca Biological Station and Laboratories. “We expect to see that with reductions in deep water oxygen, cold-water fish habitat will be lost. Low oxygen environments can also alter nutrient cycles in ways that reduce water quality. Our research highlights how long-term changes in oxygen in lakes may ultimately cascade to people by threatening economic activity and human health.”
There is little hope that the planet is going to be start cooling. In fact, climate scientists forecast we are going to get considerably hotter. Last week, The National Oceanic and Atmospheric Administration reported that May’s average carbon dioxide level 50% higher than the stable pre-industrial levels.
“Reaching 50% higher carbon dioxide than pre-industrial is really setting a new benchmark and not in a good way,” said Cornell University climate scientist Natalie Mahowald, who wasn’t part of the research. “If we want to avoid the worst consequences of climate change, we need to work much harder to cut carbon dioxide emissions and right away.”
Deeper droughts, more devastating wildfires, more powerful storms, and more flooding downpours are also the consequences of a warmer planet. Oceans become more acidic, killing off even more ecosystems and the species that depend on them.
With the planet continuing to warm, the best way to maintain oxygen at levels that support aquatic life is to keep the nutrients that create algae blooms out of them. “We know what to do to improve water quality,” Hansen said.
“The state’s saving grace is that it still has many lakes that are deep enough to remain cold at their bottom and that are surrounded by enough intact forests to keep excess nutrients out,” Stanley writes. “The state started a triage program, of sorts, over the past decade to focus
on protecting forested lands around 175 ‘refuge lakes’ that weren’t already too far gone to save.”
These saving graces don’t apply to many of western Minnesota’s lakes, which are shallower. What is their future in a warming world? And what steps can we take to ensure our lakes stay healthy for future generations to enjoy?
“What we found is that if you can keep 75% of a lake’s watershed with some kind of permanent vegetation, it’s going to maintain good water quality,” Peter Jacobson, retired DNR research supervisor, told Stanley. While such a strategy might work for lakes in wooded lands to the north, it will be more of a challenge for watersheds in Minnesota’s western and southern counties dense with farming operations.
Through its watershed districts and the state’s buffer law, Minnesota has been working to reduce the amount of phosphorus and nitrogen runoff into streams, sloughs, and lakes. However, while we have made a good start, even more must be done to protect the quality of our state waters.