The Gulf of Mexico dead zone – an area of low to no oxygen that can kill fish and other marine life – seems to be a bit better here in 2018 than last summer. The National Oceanographic and Atmospheric Administration (NOAA) predicts the Gulf of Mexico dead zone will be about average in dimension by the end of the summer. That’s good news, right? Well, not exactly. The dead zone remains 3X larger than long-term established targets. It’s clear that more nutrient strategies need to be enacted by farmers, within wastewater management infrastructures, and in home landscaping to reduce the Gulf of Mexico dead zone for coming generations.
Because state nutrient reduction strategies continue to serve as the cornerstone for reductions in each of 31 states plus 2 Canadian provinces that drain into the Mississippi River, mitigation approaches for the Gulf of Mexico’s dead zone need to be multi-faceted. The Gulf’s hypoxic zone, or dead zone, is caused by excess nutrient pollution. According to NOAA, this pollution is primarily from human activities in the watershed, such as urbanization and agriculture. The excess nutrients stimulate an overgrowth of algae, which then sinks and decomposes in the water. The resulting low oxygen levels near the bottom are insufficient to support most marine life.
The Interagency Mississippi River and Gulf of Mexico Hypoxia Task Force (HTF), a group charged with reducing the Gulf dead zone, addresses excess nitrogen and phosphorus loads in the Mississippi/Atchafalaya River Basin and outlines strategies to decrease the size of the Gulf hypoxic zone.
What’s at Stake in the Mississippi/ Atchafalaya River Basin
The Mississippi/Atchafalaya River Basin (MARB), which encompasses both the Mississippi and the Atchafalaya River Basins, is the 3rd largest in the world, after the Amazon and Congo basins. The increased amount of river dredging, levee building, and construction that comes along with this traffic impairs aquatic life in many ways by disturbing habitat. Over the years, traffic on the river has caused increased bank erosion, turbidity, sediment resuspension, and disruption of native species.
Higher river discharge in May carries a larger nutrient load into the Gulf of Mexico, one factor that contributes to a larger hypoxic zone. “While recent trend results show nutrient loads decreasing in some areas of the Mississippi-Atchafalaya watershed, on balance there has been little change in loading to the Gulf in recent decades,” said Don Cline, associate director for the U.S. Geological Survey (USGS) Water Mission Area.
Here are the recent numbers to know about the Gulf of Mexico dead zone.
- The Gulf of Mexico dead zone in 2018 is approximately 5,780 square miles, the size of Connecticut.
- This area is similar to the 33-year average of 5,460 square miles (between 1980 and 2017).
- This year’s dead zone is smaller than the 8,776 square mile 2017 Gulf of Mexico dead zone, which was the largest dead zone measured since mapping began in 1985.
- Near-average river discharge carried 115,000 metric tons of nitrate and 18,500 metric tons of phosphorus into the Gulf of Mexico in May, 2018.
- These nitrate loads were about 13% below the long-term average, and the phosphorus loads were about 10% above the long-term average.
- Interim Target: A 20% reduction of nitrogen and phosphorus loading by 2025, relative to the 1980-1996 baseline average loading to the Gulf, is the short-term goal.
- Long-Term Goal: Reducing the size of the hypoxic zone to less than 5,000 km2 by 2035 is imperative.
Watersheds experience enormous amounts of impacts associated with high nutrient concentrations. Such impacts include affected groundwater, higher drinking and wastewater treatment costs, and wasted fertilizer applications (much of the latter of which comes from fossil fuels).
“The Gulf’s recurring summer hypoxic zone continues to put important habitats and valuable fisheries at risk,” said Steve Thur, director of NOAA’s National Centers for Coastal Ocean Science. “Although there has been some progress in reducing nutrients, the overall levels remain high and continue to strain the region’s coastal economies.”
The Problem with Nutrients
Nutrient pollution is one of the most widespread, costly, and challenging environmental problems in the US. It is caused by excess nitrogen and phosphorus in the air and water. Excess nutrients stimulate an overgrowth of algae, which then sinks and decomposes in the water. The resulting low oxygen levels near the bottom are insufficient to support most marine life.
Historically, by neutralizing some of the flow energy of the water, the coastal marshes of Louisiana provided a natural barrier against erosion caused by the fierce storms which often come from the Gulf. However, the natural capacity of the MARB to remove nutrients has been diminished over the years by a range of human activities.
- The Mississippi is one of the most heavily engineered rivers in the United States.
- Over time, the character of the old river meanders and floodplains have been modified for millions of acres of agriculture and urbanization.
- Many of the original freshwater wetlands, riparian zones, and adjacent streams and tributaries along the Mississippi have been disconnected from the river by levees and other engineering modifications.
- A loss of habitat for native plants and animals has reduced the biological productivity of the entire river basin.
- Channelization has neutralized the flow of energy and MARB capacity.
“The hypoxic zone in the Gulf of Mexico forms every summer and is the largest in North American coastal waters. Freshwater and plant nutrients—mostly from unused agricultural fertilizer, and urban and industrial wastewater—travel to the Gulf from the Mississippi River,” says Katja Fennel, an oceanographer at Dalhousie University. “These nutrients stimulate a sequence of biological transformations in coastal waters that significantly decrease oxygen levels near the bottom, resulting in an environment unable to support most higher marine life forms.”
Monitoring the Gulf of Mexico Dead Zone
The HTF continues to work with land grant universities in the HTF states and other partners with similar goals. These partnerships are critical to success, helping the HTF meet research and outreach needs and carry out the ecosystem and watershed restoration actions that will reduce nutrient loads.
The forecast is based on nitrogen runoff and river discharge data from the USGS. The USGS operates more than 3,000 real-time stream gauges, 60 real-time nitrate sensors, and 35 long-term monitoring sites throughout the Mississippi-Atchafalaya watershed.
NOAA and its partners continue to develop additional hypoxia forecast capabilities. For example, new forecasts are being used to evaluate the impacts of reducing phosphorus on dead zone size and to better estimate the timing and location of hypoxia occurrence. NOAA also provides information to farmers through its Runoff Risk Forecasts, which are aimed at reducing nutrient pollution by giving farmers information about when to apply fertilizers to their fields. Such forecasts can help farmers ensure that fertilizer stays on fields, instead of washing off into waterways.
A NOAA-supported monitoring survey will confirm the size of the 2018 Gulf dead zone in early August.
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