Potential of water quality wetlands to mitigate habitat losses from agricultural drainage modernization

Abstract

Given widespread biodiversity declines, a growing global human population, and demands to improve water quality, there is an immediate need to explore land management solutions that support multiple ecosystem services. Agricultural water quality wetlands designed to provide both water quality benefits and wetland and grassland habitat are an emerging restoration solution that may reverse habitat declines in intensive agricultural areas. Installation of water quality wetlands in the Upper Midwest, USA, when considered alongside the repair and modification of aging agricultural tile drainage infrastructure, is a likely scenario that may mitigate nutrient pollution exported from agricultural systems and improve crop yields. The capacity of water quality wetlands to provide habitat within the wetland pool and the surrounding grassland is not well-studied, particularly with respect to potential habitat changes resulting from drainage infrastructure upgrades. For the current study, we produced spatially explicit models of 37 catchments distributed throughout an important region for agriculture and biodiversity, the Des Moines Lobe of Iowa. Four scenarios were considered - with and without improved drainage and with and without water quality wetlands - to estimate the net potential habitat implications of these scenarios for amphibians, grassland birds, and wild bees. Model results indicate that drainage modification alone will likely result in moderate direct losses of suitable amphibian habitat and large declines in overall habitat quality. However, inclusion of water quality wetlands at the catchment scale may mitigate these amphibian habitat losses while also increasing grassland bird and pollinator habitat. The impacts of water quality wetlands and drainage modernization on waterfowl in the region require additional study.

Keywords: Agricultural intensification; Amphibians; Corn belt; Grassland birds; Pollinators.

Fig. 1.

Diagram of a catchment indicating subsurface drainage district mains and laterals, cropped depressions, and the location of a water quality wetland positioned to capture a large portion of the flows from the catchment. Excess soil water enters field drainage tiles (not shown) before entering the drainage district main and lateral tiles and ultimately exiting the catchment at the outlet (Ditch/Waterway). Adapted from Mitchell et al. (2022).

Fig. 2.

Model catchment locations (dark blue) within the Des Moines Lobe of Iowa (DML-IA; light blue). Grey polygons indicate the location of glacial moraines within the DML-IA. Note that some model catchments are directly adjacent to one another and appear as one catchment at this scale. Adapted from the Iowa – Landforms Regions and Features layer produced by Iowa DNR, Iowa Geological Survey, and the Iowa State University GIS Facility.

Fig. 3.

Model inputs, intermediate steps, and outputs for the InVEST habitat quality model (left) and crop pollination model (right).

Fig. 4.

Land use and land cover designations for the four model scenarios (A) baseline; B) drainage modernization; C) water quality wetland; and D) drainage modernization and water quality wetland) in an example catchment. The catchment is delineated by the white outline. Corn, soy, and grassland depressional areas are indicated using a different shade of their respective land cover class colors. Modeled drainage modernizations only influence drained depressions within model catchment boundaries. LI = low intensity; MI = medium intensity; HI = high intensity; Herb. = herbaceous; Hab. = ; depress. Grass. = depressional grassland; WQ = water quality.

Fig. 5.

Suitable amphibian habitat in four example model catchments (white border). Water quality wetlands (orange border) and surrounding conservation easements (black border) are shown, together with suitable habitat gained from the addition of the modeled water quality wetland (green areas), lost suitable habitat due to drainage modernization (red areas), and suitable amphibian habitat in all scenarios (blue areas). Panel D represents stacked water quality wetlands across two catchments. Basemap imagery from United States Department of Agriculture’s National Agriculture Imagery Program (NAIP).

Fig. 6.

Suitable grassland bird habitat in four example model catchments (white border). Water quality wetlands (orange border) and surrounding conservation easements (black border) are shown, together with additional suitable amphibian habitat resulting from the addition of the modeled water quality wetland (green areas), lost suitable habitat due to water quality wetland installation (red areas), suitable habitat gained from drainage modernization (purple areas), and suitable amphibian habitat in all scenarios (yellow areas). Basemap imagery from United States Department of Agriculture’s National Agriculture Imagery Program (NAIP).

Fig. 7.

Total wild bee pollinator abundance for the A) baseline, B) drainage modernization, C) water quality wetland, and D) drainage modernization and water quality wetland scenarios for an example catchment (white border), model water quality wetland (orange border), and surrounding conservation easement (black border).