Nutrient retention of newly restored wetlands receiving agricultural runoff in a temperate region of North America

Abstract

Globally, eutrophication is deemed to be the greatest threat to freshwater resources and is particularly problematic for large shallow lakes where the prevalence of cyanobacterial blooms has increased in recent decades. Restored wetlands have been identified as natural infrastructure that can reduce nutrient loads from agricultural landscapes, thereby reducing eutrophication in downstream freshwater systems. While restored wetlands are generally accepted as efficient nutrient transformers and processors, there are relatively few studies that examine nutrient retention based on detailed hydrological budgets across seasons. We determined the nutrient retention capacity for phosphorus and nitrogen species of newly restored wetlands (<8 years old) receiving nonpoint source agricultural runoff over two water years. These restored wetlands are located in an intensive agricultural region that contributes to the central and western basin of Lake Erie. Two-year mean TP and TN wetland retention capacities were 11.7 ± 5.9 and 261.2 ± 112.3 kg ha−1 yr−1, respectively. Two-year mean TP and TN wetland retention efficiencies were 46 ± 13 and 47 ± 8%, respectively. The mean SRP retention capacity and reduction efficiency over the two-year monitoring period were 4.8 ± 1.7 kg ha−1 yr−1 and 60 ± 11%, respectively. Investigating data over two water years revealed that nutrient retention was noticeably different across seasons for both TP and TN, with the highest retention occurring in summer for TP (5.7 ± 2.7 kg P ha−1) and in the spring for TN (99.9 ± 50.0 kg N ha−1). Our findings demonstrate that restored wetlands in agriculturally intensive temperate regions designed primarily for wildlife habitat can effectively reduce nonpoint source nutrients under a range of hydrological conditions. However, further research is needed to investigate the long-term effectiveness of restored wetlands as natural infrastructure for nutrient reduction, and to evaluate the potential environmental trade-offs and economic benefits of their implementation.