July 2009, Vol. 21, No.7

GIS Mapping Reveals Targets for Reducing Gulf Dead Zone


Several environmental organizations, watershed alliances, and research groups are focusing attention on U.S. Geological Survey (USGS) data ranking the top 150 watersheds contributing nutrients to the Mississippi and Atchafalaya river basins, which drain to the Gulf of Mexico and, according to USGS, contribute about 50% of its total nutrient load.

Various watchdog groups are advocating that the U.S. Department of Agriculture (USDA) and the U.S. Environmental Protection Agency (EPA), based on the USGS data, refocus various funding efforts, such as the Farm Bill, to the top-ranking watersheds and also are urging states to establish nutrient criteria.

The USGS geographic-information-system-based study of urban- and agricultural-derived constituents generated by crop fertilization and significant animal-manure wastestream has been ongoing since the mid-1990s. The most recent report, “Incorporating Uncertainty into the Ranking of SPARROW Mode Nutrient Yield,” addresses confidence in the suspect watershed rankings, as prompted by subsequent data reviews and questions by states.

Various watchdog groups are advocating that the U.S. Department of Agriculture (USDA) and the U.S. Environmental Protection Agency (EPA), based on the USGS data, refocus various funding efforts, such as the Farm Bill, to the top-ranking watersheds and also are urging states to establish nutrient criteria.

Petitioning EPA Enforcement
The Gulf Restoration Network, a Louisiana-based group that works on water quality, wetlands, and fisheries sustainability issues in the Gulf of Mexico, is concerned that the hypoxic, or “dead,” zone in the gulf is about the size of New Jersey, more than 20,000 km2, according to Matt Rota, the network’s water resources program director. “It’s doubled in size over the last 20 years,” he said, noting that brown shrimp catches and other stocks have been greatly reduced.

The organization, along with 11 others from nine states, filed a petition in August 2008 for EPA “to set and enforce” federal standards for nitrogen and phosphorus, with which the states will be required to comply. The petition asked for a total maximum daily load for the entire Mississippi and for the nine states to promulgate nutrient criteria.

While EPA has not responded, it held a conference with several petitioners on May 5 to discuss several related issues and tasks on which the agency is working.

Also, a November 2007 draft report by EPA’s Science Advisory Board (SAB) Hypoxia Panel made some specific suggestions based on the USGS SPARROW data and requested specific reduction targets.

SAB’s “point was to target the areas that had the highest yield,” said Nancy Rabalais, aquatic ecologist and executive director of Louisiana Universities Marine Consortium (Chauvin), which measures and investigates the hypoxic zone. “The best way to do that is best management practices of all kinds,” she said.

Rabalais named numerous fertilizer approaches, manure management techniques, and watershed strategies that SAB recommended in its draft report.

In its 2008 Gulf Action Plan, the Mississippi River–Gulf of Mexico Watershed Nutrient Task Force, in which EPA is a participant, acknowledged major goals laid out in the SAB report, as well as plans to keep the momentum going, according to Darell Brown, deputy director of oceans and coastal protection in EPA’s Office of Water.

Nutrient Limits Key
The SPARROW report data show that nine of 31 Mississippi and Atchafalaya river basin states are responsible for 70% of the combined nitrogen and phosphorus loads, according to Rota. They are Illinois, Iowa, Kentucky, Mississippi, Indiana, Missouri, Arkansas, Tennessee, and Ohio.

“Once you establish nutrient criteria, you’ll see a number of streams going on [Clean Water Act Sec.] 303(d) [impaired waters] lists,” said Jason Flickner, Kentucky Waterways Alliance water resources program director. Then, he said, total maximum daily loads will be developed, and states will allocate more resources and funding to targeting sources in order to comply.

The SPARROW data “demonstrate that pollution doesn’t respect state boundaries,” Rota said.

Data Detail Widespread Loading
Dale Robertson, a USGS research hydrologist in Middletown, Wis., co-author of the recent SPARROW report, and project chief of SPARROW, cautioned that while the confidence study aimed to determine how many watersheds it would take to achieve a 50% reduction to meet the task force’s goals, “big areas need addressing.”

Although the study may have been expected to reveal that huge reductions could be achieved by focusing on particular watersheds, “it doesn’t,” Robertson said. “In order to address the top [watersheds], you’d have to go after a number of others that are similar.”

The current 4-year, approximately $300,000 SPARROW project estimates nutrient loading in both the Great Lakes and Mississippi River basins and is funded by EPA as part of its effort to obtain data for its National Water Quality Inventory reporting, as well as to support the action plan.

Robertson said that the main incentive behind recent SPARROW research on the Mississippi River basin watershed is gulf hypoxia and that EPA is looking for the highest-opportunity watersheds to effect change. The data and confidence study reveal that attacking the problem is not going to be easy.

Corn Production Worries
The current state nutrient rankings are based on data from 1992, as well as some from 2002. Therefore, they do not reflect recent changes, such as refined inputs of effective wastewater treatment and more accurate USDA fertilizer data, which — due to the nature of U.S. privacy laws — are based on sales, rather than specific farm applications, Robertson said.

Eight-hundred-eighteen HUC8 (subbasin-level) watersheds, each representing an area of 3000 km2, were outlined in the study. The top 150, ranked at 75%, 90%, and 95% confidence levels, are mostly in the corn belt and urban centers, Robertson said. “That’s where most of the nutrients are coming from,” he said.

“It’s what the last 2 years’ worth of data have indicated,” Rabalais said.

Rabalais noted that while not determined a causal relationship, there was an increase in both acreage of corn production and fertilizer sales in 2007 and 2008 and an increase in the concentration of nitrates in the Mississippi River.

“We’re worried that corn production and corn-based ethanol could exacerbate the size of the dead zone,” Rota said.

Because the SPARROW graphics show that the top-ranked watersheds are clustered in the heartland, when model results were first released, watershed managers from such states as Illinois and Iowa called Rota, surprised at the results.

This changed the scope of the SPARROW project and prompted the confidence study, Robertson said.

What’s Next for SPARROW
Robertson and his team are moving into the next phase of the project and using the most up-to-date known data on fertilizer, manure, and point source urban inputs from 2002 to update rankings.

The USGS team also is working on reducing the SPARROW watershed scale to an HUC10 or HUC12 (watershed- or subwatershed-level) watershed. Although it is possible to get down to a 50-km (30-mi) countywide scale with satellite data, key data on individual practices are unavailable and preclude modeling at this level.

The biggest criticism of the SPARROW data, Robertson said, is a lack of information on how best management practices affect nutrient loading, and some USDA best management practices data are expected to be incorporated into the next model.

Goals and Dollars
In the 2001 action plan, the task force had a goal of reducing the hypoxic zone to a 5-year running average of 5000 km2 by 2015; however, the SAB report said that it may no longer be possible and made recommendations for moving forward. “Accordingly, it is even more important to proceed in a directionally correct fashion to manage factors affecting hypoxia than to wait for greater precision in setting the goal for the size of the zone,” the report says. “Much can be learned by implementing management plans, documenting practices, and measuring their effects with appropriate monitoring programs.”

SAB recommended a dual-nutrient strategy — the 2001 action plan focused on nitrogen only — targeting a 45% minimum reduction in riverine total nitrogen flux (approximately 871,000 Mg/yr [960,000 ton/yr]) and a 45% minimum reduction in riverine total phosphorus flux (approximately 75,000 Mg/yr [83,000 ton/yr]).

The watchdog groups are aiming to ensure that current funding sources are funneled to the top 150 SPARROW-ranked watersheds, “making sure farmers within highly contributing watersheds are targeted to get a good percentage,” Rota said.

Findings presented in the SAB report generally support this perspective. “Spatial-scale issues are critical in targeting implementation actions, funding, and resources to areas with the greatest potential for improvement,” the report says.

However, Robertson noted that “the models that we have out there are pretty ‘noisy,’” and that the SPARROW confidence study “really showed that to improve things in the gulf, you can’t just address the top 150.”

While going after point sources is quick but costly, “actions are going to have to be taken throughout,” Robertson cautioned.

The silver lining of the confidence study is that USGS has a better understanding of how strong the models are, and EPA and others can devote resources to more critical basins.

“We think that the SPARROW model will help point the way to determine which watersheds deliver the highest amount of nutrients to the Gulf of Mexico and will target resources for reducing the loads,” Brown said.

While the 2008 action plan has retained the 2015 goal to “make significant progress toward” a hypoxic zone limited to a 5-year running average of 5000 km2, the plan indicates that legislative, regulatory, and financial support are critical, the report says. Current resources “are insufficient to attain the goals of the action plan,” according to the report.

For more information, see www.epa.gov/msbasin.

Andrea Fox, WE&T