Ecosystem services in Iowa agricultural catchments: Hypotheses for scenarios with water quality wetlands and improved tile drainage.

Abstract

Nutrient loads from agricultural runoff in the upper Midwest continue to contribute to Gulf Coast hypoxia and harmful algal blooms due to insufficient retention of nitrogen (N) and phosphorus (P) associated with row crop agriculture and highly productive soils. In the coming decades, much of the drainage infrastructure in this region will be rebuilt to modern design standards. At the same time, the region is developing and implementing strategies to reduce nutrient export. A group of Iowa stakeholders representing agricultural producers, land managers, and researchers met seven times in late 2018 and early 2019 and was asked to describe ecosystem service information needs that could support nutrient best management practice decisions in Iowa. The stakeholder group identified the importance and relevance of a catchment-scale (i.e., small watershed) analysis of a set of priority ecosystem services associated with agricultural tile drainage improvements and targeted water quality wetlands. Water quality wetlands are wetlands installed strategically to intercept agricultural drainage channels and receive runoff and tile drainage. These potential modifications were codified into four scenarios for literature analysis and hypothesis development including (1) a baseline, no change scenario representing the most prevalent current landscape with underperforming tile drainage infrastructure and degraded wetland functions; (2) upgrade of tile drainage infrastructure without a water quality wetland; (3) installation of a water quality wetland at the drainage district catchment scale but with no drainage improvements; and (4) a combination of adding a water quality wetland and tile drainage infrastructure upgrades at the catchment scale. Synthesizing published field-scale and modeling results across a collection of relevant studies suggests that the combined scenario of improved drainage paired with a water quality wetland may result in increased crop yields, habitat, pollination, and educational and cultural services as well as decreased global warming potential relative to the baseline scenario. Nitrate ( ${\text{NO}}_3^{-}$ ) export will likely decrease in the combined scenario, depending on net agricultural export and wetland effectiveness. To better substantiate these findings, more catchment-scale research in the region is required, particularly in the areas of water quality, wetland carbon (C) sequestration, wetland habitat quality, and educational and cultural services. Additionally, research is needed to address the effect of upgrading drainage infrastructure on ecosystem services, as most reported ecosystem service effects have been for new drainage installations. Fully integrated assessments, particularly at the catchment scale, will be key to understanding how land management approaches like adding water quality wetlands and improved drainage affect both agricultural production and ecosystem services.