hypoxia

Oxygen Loss In Lakes | Earth Wise

January 13, 2023 By EarthWise Leave a Comment

Researchers from Cornell University and Rensselaer Polytechnic Institute have found that the continual warming in the world over the past 25 years has been reducing the amount of oxygen in many lakes.

Data from more than 400 lakes – mostly in the United States – shows that lakes with dissolved oxygen losses strongly outnumber those with gains. Overall, the researchers found that the amount of low oxygen water is increasing by 0.9% to 1.7% per decade on average and the volume of lake water lacking oxygen has increased by more than 50% from 25 years ago.

In the summer, lake surfaces may be about 70 degrees while the lake bottom may be about 40 degrees. The colder water is denser than the warmer water which causes resistance to the layers mixing. It is akin to having oil and vinegar in a cruet. This is known as stratification. The result is that oxygen from the atmosphere is prevented from replenishing dissolved oxygen in deep waters. This is a normal seasonal phenomenon.

However, with winter ending sooner than it used to, seasonal stratification is starting earlier and ending later. As warming continues, it is likely that there will be an increasing number of oxygen-depleted lakes in the future.

Oxygen deprivation in water can lead to hypoxia (low oxygen) and even anoxia (no oxygen), which have negative consequences for fish and other species. Reducing oxygen in lake water can lead to buildup of methane. Nutrients from agricultural runoff, released from unsettled lake sediment, increase the likelihood of harmful algal blooms.

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Warming climate prompts harmful oxygen loss in lakes

Photo, posted June 23, 2010, courtesy of Alexander Acker via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

The Gulf Of Mexico Dead Zone | Earth Wise

July 19, 2021 By EarthWise Leave a Comment

Every summer, a so-called dead zone forms in the Gulf of Mexico. It is primarily caused by excess nutrient pollution from human activities in urban and agricultural areas throughout the Mississippi River watershed.

When these excess nutrients reach the Gulf, they stimulate excess growth of algae, which eventually die and decompose, depleting oxygen as they sink to the bottom. These low oxygen levels near the Gulf bottom cannot support most marine life. Animals that are sufficiently mobile – such as fish, shrimp, and crabs – generally swim out of the area. Those that can’t move away are stressed or killed by the low oxygen.

A team of scientists funded by the National Oceanic and Atmospheric Administration issues an annual forecast for the dead zone based upon a suite of models that incorporate river flow and nutrient data.

The 2021 forecasted area is somewhat smaller than, but close to, the five-year measured average for the dead zone, which is 5,400 square miles, roughly the size of the state of Connecticut. Each year, these forecasts are reported as comparisons to long-term averages, but the problem is that the long-term average is unacceptable.

The Interagency Mississippi River and Gulf of Mexico Hypoxia Task Force has set a goal of reducing the size of the dead zone to a five-year average of 1,900 square miles – about a third of the current average.

Large reductions in nutrient loads have been called for in federal and state action plans for nearly 20 years, but clearly these reductions have not yet been sufficient. The Interagency Task Force continues to provide information for managing nutrient loads in the Mississippi River Basin.

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Average-sized ‘dead zone’ forecast for Gulf of Mexico

Photo, posted October 6, 2020, courtesy of Christine Warner via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Forecasting A Massive Dead Zone

June 18, 2019 By EarthWise Leave a Comment

The Gulf of Mexico dead zone occurs every summer, and is considered one of the largest dead zones in the world. This cyclical event occurs where the Mississippi River empties into the Gulf of Mexico, just off the coast of Louisiana and Texas.

This annual dead zone is primarily caused by excess nutrient pollution from human activities, such as urbanization and agriculture, occurring throughout the Mississippi River watershed. Washed off the land by spring rains, these excess nutrients stimulate an overgrowth of algae once they reach the Gulf of Mexico. The algae in the Gulf eventually die, and then sink and decompose in the water. The resulting area of the ocean ends up with a condition known as hypoxia, which is an insufficient amount of oxygen to support most marine life. In hypoxic or dead zones, animals that can’t swim away will often suffocate and die.

Scientists from the National Oceanic and Atmospheric Administration estimate that this year the dead zone in the Gulf of Mexico will be approximately 8,000 square miles, which is roughly the size of Massachusetts. The research team uses U.S. Geological Survey river flow and nutrient data to make its forecast.

According to NOAA, the abnormally high amount of spring rainfall is a major factor contributing to this year’s dead zone. Last month, nitrate loads entering the Mississippi River watershed were 18% above the long-term average, and phosphorus loads were about 49% above the long-term average.

While the 2019 forecast is slightly less than the record size of more than 8,700 square miles set in 2017, it’s still much larger than the five year average size of 5,700.

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Very large dead zone forecast for the Gulf of Mexico

Massive 8,000-mile ‘dead zone’ could be one of the gulf’s largest

Photo, posted May 22, 2009, courtesy of Michael McCarthy via Flickr.

Earth Wise is a production of WAMC Northeast Public Radio.

Nitrogen Pollution Suffocates Fish

July 27, 2015 By EarthWise

In Riverhead, Long Island the stench of rotting fish is becoming all too familiar. Over the past two months, the Department of Environmental Conservation estimates more than 400,000 Atlantic menhaden, commonly called bunker, have washed up on the shores of the Peconic River – which sits between Long Island’s north and south forks. The culprit: nitrogen pollution.