A recent study conducted by the University of Illinois Urbana-Champaign highlights the effectiveness of wetlands in the Mississippi River Basin in removing nitrogen pollution from agricultural runoff. This research indicates that such natural systems not only improve water quality but also lead to considerable cost savings for local drinking water treatment facilities.
Wetlands play a critical role in the ecosystem, acting as “nature”s kidneys” that filter pollutants from surface water. According to the findings, these areas are instrumental in mitigating non-point source pollution, a significant contributor to deteriorating water quality across the United States. Nutrient runoff from farming can trigger harmful algal blooms and create hypoxic zones, affecting both aquatic life and drinking water safety.
“While many strategies to combat excess nutrients target their sources, wetlands can effectively intervene post-factum and facilitate cleanup,” stated Marin Skidmore, a co-author and assistant professor in the Department of Agricultural and Consumer Economics at the university. She elaborated that wetlands support the nitrogen cycle, promoting the conversion of nitrogen into harmless nitrogen gas.
The research focused on the Agricultural Conservation Easement Program, previously known as the Wetland Reserve Program, which encourages landowners to convert agricultural land into wetlands under long-term contracts. This initiative has seen significant participation since its inception in 1990.
Co-author Nicole Karwowski, an agricultural economist at Montana State University, noted that while prior studies often emphasized individual wetlands or specific watersheds, this research leverages extensive data to assess wetland easements” average effects over time.
The analysis, which covered data from 1990 to 2018, revealed that approximately 9,000 permanent easements had been established, encompassing around 0.22% of the land within the basin. The researchers evaluated water quality trends at the sub-watershed level, examining the impacts on phosphorus, ammonia, and total Kjeldahl nitrogen (TKN) concentrations.
Results showed an impressive 62% reduction in ammonia levels and a 37% decrease in TKN shortly after wetland restoration, with improvements becoming evident within three years and likely persisting for over a decade. “These results are significant, especially given the challenges Illinois and adjacent states face in regulating nitrogen levels as outlined in the Nutrient Loss Reduction Strategy,” Skidmore remarked.
While the study did not identify substantial long-term effects on local phosphorus concentrations, some downstream reductions were noted. The presence of cropland in the watershed was also analyzed for its influence on nutrient runoff.
Karwowski expressed optimism about the findings, indicating that wetlands can effectively filter high-nutrient waters, countering concerns about nutrient overload. The research also assessed potential financial implications for local water treatment facilities. Under the Safe Drinking Water Act, public systems must adhere to strict nitrate limits, which often necessitate costly treatment technologies as nitrogen levels rise.
The team estimated that restoring 100 acres of wetland could reduce annual treatment costs for a large public water system by up to $17,000. Initial investments in wetland restoration may yield returns within 20 to 30 years, with potential annual benefits reaching $200 million.
Skidmore noted that the wetland easement programs represent a financial transfer from the federal government to local communities, with savings aligning with federal expenditures in nitrogen mitigation.
The study”s implications gain importance following a recent Supreme Court ruling that restricts protections for wetlands adjacent to navigable waters, potentially impacting 72% of Illinois wetlands and increasing the risk of development that undermines their ecological benefits.
Future research by Skidmore and Karwowski aims to explore how the distance of wetlands from streams or rivers influences their pollutant removal effectiveness. Initial findings suggest that even non-adjacent wetlands provide substantial water quality improvements.
“Our results should inform policymakers about the vital role wetlands play and the necessity of their protection,” Skidmore concluded. “These ecosystems can complement other nutrient reduction strategies, creating a more effective approach for agricultural areas.”
The full study, titled “Nature”s Kidneys: the Role of Wetland Reserve Easements in Restoring Water Quality,” is published in the Journal of the Association of Environmental and Resource Economists.
