Indian Creek Watershed Project Improves Water Quality

The results of the Indian Creek Watershed Project in Lake County, Ill., were tallied, and water quality improved as acreage participation increased in the nutrient management program that partnered local farmers with local, state, and national agencies, crop specialists and agribusinesses.

The watershed plan was to increase the area that had best management practices from an initial starting point of around 10% in 2010 to greater than 50% of the 51,243-acre area in 2015.

“At which time cover crops were planted in 5% of the watershed, and on-field nitrogen management was used in greater than 50% of the watershed, which we would expect to reduce nitrogen runoff,” said Ursula Mahl, University of Notre Dame senior research technician. “Indian Creek is a great case study to show how watershed-scale conservation has the potential to both support productive agriculture, as well as improve water quality.”

Outlet flow was measured with a U.S. Geological Survey gauge and surface water nitrate was measured using a combination of grab samples one to four times monthly beginning in May 2010 on one to five sites located at the top and bottom of each sub-watershed. Data also was collected from a sensor at the outlet to measure nitrate continuously starting in July 2011.

“We predict that because precipitation and flow affect nitrogen runoff that we should see similar patterns for flow and for nitrate export when we compare between sites and years. However, if conservation efforts reduce nitrate runoff from fields leading to lower concentration, nitrate export will also be lower than we would expect based purely on flow,” Mahl said.

The success of nutrient management hinges on a collective effort by farmers.

“In our lab, we looked at a number of practices for in-field and edge-field, including cover crops for their capacity to retain nitrogen and phosphorous on the field, as well as something called a two-stage ditch, where you put mini floodplains inside the inset channel to minimize the bank failure and erosion and also to clean up the water for whatever nitrogen has gotten into the field,” Mahl said.

“But we found that none of these are a silver bullet and they always work better in combination, and you also can’t expect one field to do the work for the entire watershed. You really need to have some kind of conservation on every field to be effective because you’re only going to remove a portion of whatever load is coming off of each of those fields. The objective of our part of this project was to determine how these changes affected water quality.”

The water quality findings include: 

• Nitrate concentrations and yields were similar for downstream sites, which suggests uniform effects of conservation on nitrogen inputs throughout the watershed.
• Seventy percent to 80% of the annual nitrate export occurred during elevated flow with 30% to 60% of this occurring during large storms.
• Despite high annual variations in flow and nitrate, including the 2012 drought, a trend was detected of decreasing nitrate export over time, from 2013 to 2015.
• With nitrate export in 2013 being greater than 2015 for similar-sized storms, this suggests that implementation of best management practices, particularly those that decrease runoff could improve water quality.
• Given that nitrogen loss can account for up to half of the fertilizer application, practices that improve nitrogen-retention in fields are critical.

Source: AgriNews