Forthcoming Research Paper

29 Years of Nutrient and Element Sequestration in Two Constructed Riverine Wetlands

by Daniel Ruane, Jay Martin, Blanca Bernal, Christopher Anderson,  Robert Nairn, and William J. Mitsch

Abstract

In recent decades, the implementation of constructed wetlands has become an increasingly popular management practice in various settings due to their ability to improve water quality with natural processes. Physicochemical properties of wetland soils impact removal and retention pathways for multiple species of interest, such as nitrogen, phosphorus, and metals. While the impacts of soil characteristics on water treatment processes is understood, it is unknown how these soils evolve long-term. The Olentangy River Wetland Research Park (ORWRP) is an ideal study site to address this gap in knowledge. The site features two experimental wetlands constructed in 1993 with ample data sets published since its inception. We used soil core samples to quantify storage and accumulation of nutrients and elements and identify long-term trends over 29 years. Our results indicate that, similar to previous carbon studies, the nutrient content and storages in both wetlands’ soils have stabilized over time and have amounts comparable  to other constructed wetlands. Average nitrogen and phosphorus storage were 0.29 kg N m-2 and 31.9 g P m-2, which equate to accumulation rates of 0.01 kg N m-2 yr-1 and 1.06 g P m-2 yr-1 since they were constructed. Element contents and storages have changed through time with vertical accretion of soil, with higher amounts in lower depths of soil indicating permanent storage. These wetlands demonstrate the net benefit of constructed wetlands in society, and the importance of management practices to maximize their benefits. Our results indicate that constructing wetlands with high surface area of shallow regions to increase macrophyte cover and excavating deeper regions to increase volume subject to sedimentation are among the most effective ways to extend the duration of greater rates of nutrient reduction.