A new study by the U.S. Geological Survey (USGS) and the U.S. Department of Agriculture (USDA) shows that collaborative conservation and water quality efforts by farmers, ag retailers and government agencies can reduce nitrogen losses to rivers and streams by as much as 34 percent in Iowa and other states in the Mississippi River Basin.
Released last week, the study combined modeling tools from the USDA and the USGS to measure the potential effects of conservation practices. The benefits of these practices have historically been difficult to do in large river systems because water quality is influenced by a wide variety of factors, including non-agriculture practices and natural processes.
The study showed the nutrient reductions attributable to agricultural conservation practices in the Mississippi River basin region ranged from 5 to 34 percent for nitrogen. Phosphorus reductions from farmers’ conservation work ranged from 1 to 10 percent.
"I’m not surprised," says Rick Robinson, Iowa Farm Bureau environmental policy advisor. "It matches what many other studies have found, contrary to what you read and hear in the popular media, and follows the long-term commitment Iowa farms have made to conservation. We know that there’s been more conservation applied to the land since the 1990s, but scientists often find lags in seeing water quality results at the largest watershed scale for many years. The USGS study accounts for those lags and weather variations that often mask the positive effects of the conservation investment."
For example, Iowa farmers have substantially changed their tillage and other farming practices in the past decade to conserve topsoil, reduce nutrient losses and improve water quality, according to a recent Iowa Farm and Rural Life Poll. Farmers have invested as much as $2.2 billion in the last 10 years to make those conservation improvements.
The latest USGS results seem consistent with a 2014 study from the federal agency of several decades of nitrate concentration and flow data from 10 major Iowa rivers indicating that concentrations of nitrate decreased from 2000 to 2012 in all basins. A year prior to that, the USGS also reported that nitrate levels in the Iowa River decreased by 10 percent from 2000-2010 (October 2013 USGS), one of the first observed declines in the Mississippi River Basin since 1980.
Iowa is also making strides in better quantifying the extent to which conservation practices are already on the landscape, and to help farmers get the right conservation practices and structures in the right places to be most effective. The Iowa Nutrient Research and Education Council (INREC) is documenting progress on conservation and water quality efforts and also developing programs for agronomists and Certified Crop Advisors to provide farmers the information they need to address environmental needs.
INREC is a non-profit organization established by ag retailers through the Agribusiness Association of Iowa (AAI), the Iowa Farm Bureau Federation (IFBF) and other farm groups and is gearing up to be the private side of that conservation and water quality effort in Iowa.
"Progress will continue to be made in the future," Robinson said.
Increased cover crops
Iowa farmers are implementing conservation and water quality practices through the state’s water quality initiative, officially called the Iowa Nutrient Reduction strategy. Farmers in Iowa have significantly increased the planting of cover crops, up 35 percent in 2015 compared to the previous year, and have installed edge-of-field practices, such as wetlands, bioreactors and saturated buffer strips.
In the new modeling systems, researchers from the USGS and USDA were able to validate the downstream benefits of farmers’ conservation practices. Prior to this study, the agency officials said, nutrient reductions have been difficult to detect in the streams because there were multiple sources of nutrients (including non-agricultural sources) and natural processes (e.g., hydrological variability, channel erosion) that can conceal the effects of improved farming practices on downstream water quality.
Government water quality officials said the new study confirmed that collaboration by farmers and others was paying off for water quality and soil conservation.
"When multiple farmers, ranchers and working forest land managers in one region come together to apply the conservation science, the per-acre conservation benefit is greatly enhanced," said USDA Natural Resources and Environment Deputy Under Secretary Ann Mills.
Structural and erosion control practices, such as conservation tillage, in the Upper Mississippi River Basin have been shown to reduce runoff and peak flows, thereby increasing water infiltration into the soils and the subsurface geology.
An added benefit of these conservation actions is that, in some areas, hydrological and biogeochemical conditions in the subsurface can promote the removal of nitrogen by natural biological processes.
Phosphorus reductions were lower than was seen for nitrogen, possibly because of long time lags between conservation actions and the time it takes for sediment-bound phosphorus to move downstream.