279-10 The Efficacy of Constructed Vernal Pools in Sequestering Nutrients in Urban Settings

Session: The Current Understanding of the Role of Wetland Hydrology in the Cycling of Elements and other Substances: A Technical Session in Memory of Paul H. Glaser

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Urban waterways commonly have elevated levels of nutrients, like nitrogen and phosphorus, that can be sourced from stormwater runoff, wastewater discharges, and lawn fertilizer applications. Such nutrient inputs can degrade water quality in urban ecosystems. Ephemeral wetlands like vernal pools can serve as valuable nutrient management tools in urban areas, but the nutrient mitigation capacity of constructed vernal pools used in best management practice projects is poorly understood. To address this research gap, we investigated nutrient cycling in four vernal pools within an urban conservation area near St. Louis, Missouri, United States. We compared one natural, forested vernal pool with three constructed vernal pools that varied in age, vegetation type, substrate composition, and distance to a nearby urban stream. Intact soil cores from each vernal pool were collected and manipulated ex situ to simulate nutrient fluxes across the soil-water interface when the cores were inundated for a 21-day period with rainwater (three cores per site) or floodwater from the nearby stream (three cores per site). We periodically sampled the control and inundation waters for nitrate, ammonium, and phosphate. Soil nutrient characteristics in untreated cores (three cores per site) and the treated cores following the experiment were also assessed. While most nutrient species did not change in the rainwater and floodwater controls over time, we observed a significant increase in floodwater nitrate concentrations with time. This finding suggests that organic matter decomposition in urban stream floodwater is a nitrogen source. In the water columns of the experimental cores, total dissolved nitrogen generally increased over time, and the cores that were amended with floodwater usually had higher dissolved nitrogen levels than those inundated with rainwater. Despite small variations in nitrogen species dynamics across the inundation treatments, the water columns of the natural vernal pool cores exhibited similar nitrogen behavior to those of the constructed vernal pools. However, water column phosphate concentrations in the natural vernal pool cores increased significantly over time and were 4–11 times higher than the constructed vernal pool cores for both treatments. The organic matter-rich soils of natural vernal pools may therefore source more phosphorus to their water columns during inundation events compared to constructed vernal pools. Nevertheless, our findings underscore the complex interplay of vernal pool properties and inundation water types.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8324

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