Though the hypoxic zone in the Gulf of Mexico has continued to expand in recent years, a report by a Mississippi River basin taskforce to Congress shows basin states are making progress.
The U.S. Environmental Protection Agency’s report released this week, said the so-called “Dead Zone” in the Gulf covered about 6,474 square miles in 2015, about 19% above the long-term average of 5,240 square miles.
The report said the numbers are “indicating that nutrients from the Mississippi River watershed are continuing to affect the nation’s coastal resources and habitats in the Gulf. Researchers suggest that heavy rains in June and high river discharges in July may provide an explanation for the larger zone measurement.”
The hypoxic zone was not measured in 2016 because of technical problems. A limited sampling determined the Gulf was forecasted to have an “average size” hypoxic zone, according to the report.
The 2007 Mississippi River Basin Science Advisory Board Panel recommended a nutrient reduction strategy to include a 45% reduction in total nitrogen and total phosphorus loads into the Gulf to reduce the hypoxic zone.
The taskforce set an interim target of a 20% nutrient load reduction by 2025, as a milestone to achieving 45% reductions by 2035.
“The total nitrogen five-year running average for 2011-2015 was about 21% below the baseline period average,” the report said. “The total phosphorus five-year running average for 2011-2015 was about 13% above the baseline.”
The report said the five-year total nitrogen average is below the 2025 target, because it “is heavily influenced by low river flow conditions in 2012 and 2014.”
As of January 2017, all 12 states in the basin have finished drafts or have completed nutrient reduction strategies, according to the report. Those states are Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Minnesota, Mississippi, Missouri, Ohio, Tennessee and Wisconsin.
“The strategies were developed by multiple agencies and stakeholders within each state and have resulted in greater awareness of the need for nutrient reductions and, in some cases, development and implementation of new programs,” the report said.
The task force highlighted a few examples of how states are making progress in reducing nutrients runoff.
Nitrate levels in the Illinois River decreased by 21% between 2000 and 2010, making it the first time “substantial,” multiyear decreases in nitrate were observed in the Mississippi River Basin since 1980. Nitrate levels during the same period decreased by about 10% in the Iowa River.
“Reliable information availability on trends in contributing factors (e.g., fertilizer use, livestock waste, agricultural management practices, urban inputs, wastewater treatment improvements) is needed to better understand the correlation of those factors, independently and collectively, to increases or decreases in nitrate levels in streams and rivers throughout the Mississippi River Basin,” the report said.
In 2016, the taskforce said agricultural inputs including manure, fertilizer, and legume crops were the largest source of nitrogen runoff, or about 60% of the total. Fertilizers contributed about 41% of the total.
Atmospheric deposition including losses from natural, urban and agricultural sources, contributed 26%; urban sources, 14%, including an even split between urban areas and wastewater treatment plants.
Agricultural inputs including manure and fertilizers, also were the largest total phosphorus source at 49% of the total. In addition, 27% came from chemical fertilizers and 22% from manure.
The taskforce said urban sources contributed 29%, urban areas 16% and wastewater treatment plants 13%.
“Background sources of phosphorus included erosion of channels and banks of large streams where phosphorus was previously deposited from other upstream sources, deeply weathered loess soils, and forests,” the report said.
The task force points to a 2016 study that tried to validate the downstream benefits of farmers’ conservation efforts, using a model.
“This recent study demonstrates that agricultural conservation practices in the upper Mississippi River watershed can reduce nitrogen inputs to area streams and rivers by as much as 34%,” the report said.
“Nutrient reductions have been difficult to detect in the streams because changes in multiple sources of nutrients and natural processes can have confounding influences that conceal the effects of improved farming practices on downstream water quality.”
Iowa’s voluntary nutrients reduction strategy finished in 2013 was the subject of controversy among environmental groups and others who wanted the state to take a regulatory approach to reducing nutrients runoff.
The taskforce said since the implementation of the voluntary strategy in Iowa, the Water Quality Initiative as resulted in state partnerships with more than 9,400 farmers affecting more than 930,000 acres of Iowa farmland.
Read the report to Congress here.
Todd Neeley can be reached at email@example.com
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