AMES, Iowa - Do wetlands engineered for water quality treatment function in ways that provide benefits for biodiversity, similar to Iowa’s natural wetlands?
A research project led by Charlie Loewen, assistant professor in the Department of Ecology, Evolution and Organismal Biology at Iowa State University, is trying to better understand these systems, their potential benefits and unintended consequences, with support from the Iowa Nutrient Research Center.
While most of Iowa’s natural wetlands have been drained and converted to farmland or urban spaces, a slowly growing number of wetlands have been created or restored in recent decades, thanks to federal conservation programs that have helped fund their revival. A subset of these are Conservation Reserve Enhancement Program (CREP) wetlands located strategically to catch water from agricultural drainage tiles before it flows downstream.
These engineered, water quality wetlands, developed largely based on research at Iowa State, have been found to be an effective edge-of-field best management practice to reduce nitrogen.
They may also provide important habitat for waterbirds and other wildlife on Iowa’s agricultural landscapes, but these broader co-benefits depend on the ability of the wetlands to support healthy, functioning food webs, according to Loewen.
Another longstanding concern is the potential buildup of phosphorus, an element of fertilizer and manure, that can enter the wetland attached to sediments or dissolved in the tile drainage. Compared to nitrogen, CREP wetlands have much less ability to treat phosphorus. Levels can build up in the water and sediments and lead to lush growth of algae and wetland plants. When these die and decompose, "anoxia," or low oxygen levels, can result, leading to a cascade of negative impacts for aquatic wildlife.
The potential to treat nitrogen without similar reductions in phosphorus may also affect the types of organisms that can thrive in wetlands and their receiving waters.
“Could altering nutrient ratios in these systems lead to unintended consequences, for example, favoring nuisance organisms, including toxin-producing cyanobacteria?” Loewen asked.
“If there are problems, a few small wetlands are not necessarily an issue, but as we’re trying to scale up this practice to hundreds – maybe thousands - across the landscape, it’s important to understand how to optimize their benefits while also avoiding any potential problems,” he said.
Last summer, Loewen and three graduate students extensively studied nine CREP wetlands across Iowa’s Des Moines Lobe landform region, collecting samples of plants, animals and water. They took the same measurements at one “remnant” wetland and two wildlife restoration wetlands to serve as more natural reference sites for comparison.
Their major focus was to identify “bioindicators” of aquatic system health. They surveyed different levels of the wetland food-web, including aquatic plants and plant-like microorganisms (phytoplankton and periphyton) and invertebrates (including zooplankton and aquatic insects) that live either in the water or on submerged plants and bottom sediments. They noted the presence of organisms, like mayflies and damselflies, that generally signal good water quality, as well as flatworms and non-biting midges that often indicate poorer water quality and low oxygen environments.
Incorporating data on water quality from another study of the same CREP wetlands, they are also looking at how varying nutrient levels and ratios of nitrogen to phosphorus appear to influence biological communities both within the wetlands and immediately downstream.
Loewen and his research team are still analyzing the extensive data they gathered and plan to wrap up the study later in 2025.
“At this point, I describe our work as ‘squinting’ at the data as we continue counting organisms in the lab and refining our statistical analyses. We hope that our results will not only shed light on the ecological health of water quality treatment wetlands here in Iowa but also inform future design and management considerations to optimize their multiple biological values,” he said.
A final project report will be available later this year on the INRC’s website, at https://inrc.cals.iastate.edu/node/1251.
Contacts
Charlie Loewen, Ecology, Evolution and Organismal Biology, 515-294-5617, cloewen@iastate.edu
Ann Y. Robinson, Agriculture and Life Sciences Communications, 515-294-3066, ayr@iastate.edu