The Iowa Conservation Reserve Enhancement Program (CREP) is a state, federal, local, and private partnership that provides incentives to landowners who voluntarily establish wetlands for water quality improvement.
The goal is to reduce nitrogen loads from croplands to streams and rivers, while also providing wildlife habitat and increased recreational opportunities. Over the past 15 years, about 90 CREP sites have been constructed in a 37 county region in north central Iowa.
For over 10 years Dr. William Crumpton, Iowa State University professor in the department of Ecology, Evolution and Organismal Biology, has been leading the monitoring of 10-15 of the CREP sites to measure their performance.
In a new video released by the Iowa Learning Farms, Dr. Crumpton discusses how CREP wetlands function and the need for long-term delivery scale monitoring with Dr. Matt Helmers, Director of the Iowa Nutrient Research Center.
Here’s a sneak peak of their conversation:
How do CREP wetlands go about removing nitrate?
The primary process is denitrification. Denitrification is carried out by anaerobic bacteria. They use carbon as an energy source and nitrate as an electron receptor instead of oxygen. They denitrify nitrate into N2 gas -which is 80% of our atmosphere.
What factors influence their performance in removing nitrate?
1. The amount of water that goes into the wetland, also known as hydraulic loading rate. This factor is the easiest to adjust to control overall performance. If the wetland is larger, the hydraulic loading rate is smaller and the higher percentage of nitrate that entered the system is removed.
2. Temperature. Denitrification increases with warmer temperatures and slows during the cooler times of the year.
3. Incoming nitrate concentrations. If the incoming concentration is higher more mass of nitrate is removed by the wetland.
What are the habitat benefits of these sites?
The buffer area is about 3x the pool area. For example, a 10 acre CREP pool has a 30+ acre buffer around it. The buffers are seeded with native prairies mixes of grasses and forbs. Because CREP sites are designed to be wet, even in drought years these sites have not gone dry. They provide critical habitat during drought conditions.
These CREP sites are being used for projects like the Conservation Learning Labs led by the Iowa Learning Farms. Why is delivery scale level of monitoring important to helping meet the Iowa Nutrient Reduction Strategy Goals?
Delivery scale monitoring helps determine if plot scale performance results on nitrate and phosphorus reductions from various practices is what can be expected at field-level implementation.
For the CLL sites at least 50% of each watershed has been seeded to cover crops for 3 years. However, the water quality data has not yet shown a significant response. What are some factors that are contributing to the lack of response?
Scale and weather both play a role in the results. The larger system has a longer lag time compared to plot scale research. Continued long term monitoring at the delivery scale is extremely important as weather influences nutrient loading and management decisions. Both 2017 and 2018 weather limited the amount of cover crop growth, likely reducing their nutrient reduction performance. Dr. Crumpton recommends at least 10 years of monitoring to average out the weather influences on the practices performances and account for lag time in the system.
For more information on nitrate reduction wetlands in Iowa and cost-share opportunities for your farm, be sure to check out our recent virtual field day with Susan Kozak, IDALS Soil Conservation & Water Quality Division Director, and Shane Wulf, IDALS Water Resources Bureau Environmental Specialist.