GEOCHEMICAL CHARACTERIZATION OF HYPORHEIC ZONE GEOCHEMISTRY IN A BACKWATER SYSTEM: A CASE STUDY FROM FOURPOLE CREEK, HUNTINGTON, WV

Wetland environments are frequently thought of as buffer regions for nutrient fluxes into major waterways. Agricultural and environmental runoff brings nitrogen, phosphorous, and trace metals into the wetland system that changes in geochemical conditions can either mobilize or entrain within the sediment. Given the nutrient-driven occurrences of harmful algal blooms on the Ohio river, it is critical to characterize the role of backwater wetland systems in either preventing or enhancing these events. Specifically, the impact of hyporheic zone interactions must be characterized to understand microbial activity. Here we show results from the sampling of subsurface waters along the Fourpole Creek in Huntington, W.V. This backwater system fills during high water levels on the Ohio River, trapping both catchment water and Ohio River overflow. We utilized a multi-proxy geochemical approach to characterize changes in the geochemistry of the interstitial waters both along the creek and across the floodplain.

Overall, the hyporheic zone can be identified as the upper 9 inches below the sediment-water interface. This region shows different trace metal and carbon sources than deeper samples, consistent with enhanced microbial activity. Additionally, the analysis of δ¹⁸O, Δ¹⁷O, andδD show that the hyporheic zone waters are isotopically distinct from the underlying water, consistent with higher degrees of flux of fresh water and nutrients. Finally, we see changes in the δ¹³C DIC down the depth profile, supporting the hyporheic zone as a region of carbon cycling.

These results are consistent with recycling of nutrients in the hyporheic zone, likely resulting in enhanced nitrogen removal via denitrification. Future work will expand this record to more sample locations during and after flood events.