Development of a novel framework for modeling field-scale conservation effects of depressional wetlands in agricultural landscapes

Abstract

The intermixed cropland, grassland, and wetland ecosystems of the upper midwestern United States combine to provide a suite of valuable ecological services. Grassland and wetland losses in the upper midwestern United States have been extensive, but government-funded conservation programs have protected and restored hundreds of thousands of acres of wetland and grassland habitat in the region. The value of restored wetlands in agricultural fields is complex, and the USDA Natural Resource Conservation Service, Conservation Effects Assessment Project (CEAP) has been lacking the methodology to include these conservation practices in their analyses. Our aim is to develop a reproducible methodology for simulating wetlands within the CEAP cropland modeling framework used to evaluate other agricultural conservation practices. Furthermore, we evaluate the effect of using upland conservation practices on the functioning of restored wetlands. By simulating the addition of a depressional wetland that effectively removes 6% of the field from crop production, we obtained a 15% reduction in annual runoff and a 29% and 28% reduction in mean annual nitrogen (N) and phosphorus (P) losses, respectively. The presence of the depressional wetland in the field is estimated to also reduce edge-of-field losses of sediments by 20% and sediment-bound N and P by 19% and 23%, respectively. Additionally, adding a grass filter strip around the wetland greatly decreased sediment inputs to the wetland, increasing the effective life of the wetland, in terms of its ability to perform valued services, by decades to centuries. Our method for modeling depressional wetlands embedded in cropped fields provides a means to quantify the effects of wetland conservation practices on field-level losses for regional assessments, such as the CEAP.

The Potential of Prairie Pothole Wetlands as an Agricultural Conservation Practice: A Synthesis of Empirical Data

“…Based on our literature review which shows a lack of spatial range in the available empirical studies assessing wetland nutrient dynamics in the PPR, this highlights our need for more empirical studies to reveal trends in underlying mechanisms of the entire PPR landscape and improve model estimates. Mckenna et al (2020) has demonstrated a new method for simulating depressional wetlands within the Conservation Effects Assessment Project (CEAP) cropland modeling framework using Agricultural Policy/Environmental eXtender (APEX). Their results show reduced runoff from a field by 8% with incorporation of an edge-of-field wetland, a 9% reduction when adding a buffer strip between the field and wetland, and 18% reduction when converting the entire upland to grassland.…”

“…Their results show reduced runoff from a field by 8% with incorporation of an edge-of-field wetland, a 9% reduction when adding a buffer strip between the field and wetland, and 18% reduction when converting the entire upland to grassland. Additionally, reductions in sediment, nitrogen, and phosphorous entering the wetland occurred with the addition of a buffer strip and more so with the complete upland conversion to grassland (Mckenna et al 2020).…”

Prairie Pothole Management Support Tool: A web application for evaluating prairie pothole flood risk

“…Pothole‐specific conservation program trials (USDA, 2020) would also benefit from such a tool. Similarly, the potential for pothole wetlands to be included as a Conservation Effects Assessment Project (CEAP) conservation practice (McKenna et al., 2020) suggests the need for decision making tools. The objective of this technical note is to describe a web application developed for to allow users to explore flood risk of prairie potholes within the DML of Iowa based on morphologic and management characteristics.…”

Assessment of Input Parameters and Calibration Methods for Simulating Prairie Pothole Hydrology using AnnAGNPS

“…A suite of models have been developed and tested. The Agricultural Policy/Environmental eXtender (APEX) model represents potholes as idealized shapes on a generic agricultural landscape (McKenna et al, 2020). This removes key parameters that make potholes unique, which is ultimately the focus of our larger effort to provide a web tool with some level of specificity and localized application.…”