A unique aspect of the Iowa CREP is that nitrate reduction is not simply assumed based on wetland acres enrolled, but is calculated based on the measured performance of CREP wetlands. As an integral part of the Iowa CREP, a representative subset of wetlands is monitored and mass balance analyses performed to document nitrate reduction. In addition to documenting wetland performance, this will allow continued refinement of modeling and analytical tools used in site selection, design, and management of CREP wetlands.
By design, the wetlands selected for monitoring span the 0.5% - 2% wetland/watershed area ratio range approved for Iowa CREP wetlands. The wetlands also span a four fold range in average nitrate concentration, from less than 10 mg/l to over 20 mg/l. The wetlands thus provide a broad spectrum of those factors most affecting wetland performance: hydraulic loading rate, residence time, nitrate concentration, and nitrate loading rate. Wetlands are instrumented with automated samplers and flow meters at wetland inflows and outflows. Water levels are monitored continuously at outflow structures in order to calculate changes in pool volume and discharge and wetland water temperatures are recorded continuously for modeling nitrate loss rates.
Results for a site with ongoing monitoring.
