RIPARIAN NITROGEN CYCLING AND POLLUTANT REMOVAL UNDER FUTURE CLIMATE SCENARIOS

Riparian buffer zones are crucial for water quality, human health, and ecosystem function. Critical ecosystem services of riparian soils include nitrogen removal via denitrification and phosphorus retention through sorption on mineral surfaces. Soil moisture influences these processes, which will be altered by climate change. This threatens nitrogen cycle dynamics and phosphorus removal in riparian systems. To investigate potential changes, we conducted a lab experiment using soil cores. We hypothesized that climate-induced shifts in moisture dynamics would enhance phosphorus removal but hinder denitrification due to increased oxygen diffusion. Forty-eight soil cores (5cm diameter, 15cm height) were collected, and additional samples were collected for particle size, bulk density, and powder X-ray diffraction (XRD) analyses. Soil treatments were applied in a fully factorial design, considering land uses (cultivated versus uncultivated), antecedent soil moisture (field capacity versus drought), water treatment (flooding versus capillary rise), and pollutant quantity (simulated agricultural runoff versus ultrapure water). XRD analysis revealed a mixed clay mineralogy, including a mixed-layer illite-montmorillonite, IS70R1. Results showed significant changes in nitrogen cycle dynamics, with nitrogen fluxes showing evidence of Dissimilatory Nitrate Reduction to Ammonium (DNRA), Anammox, and nitrogen mineralization in cultivated and uncultivated soils. Statistical analyses of the data, primarily through generalized additive models, indicate significant individual and combined effects (p<0.05) of the simulated treatments on nitrate, ammonium, and phosphate concentrations, along with pH and ARQ. Critically, the clay mineralogy in uncultivated land use plays a statistically significant role in moderating the soil nitrogen cycle and is strongly affected by changes in land use, soil moisture, and water flow predicted in future climate scenarios. Additionally, phosphate concentrations are more affected by soil moisture, water flow, and their interactions. Correlated iron and nitrogen data indicate evidence of the Ferrous Wheel Hypothesis. Our research demonstrates that riparian biogeochemical processes are affected by different future climate scenarios.