Using a simple 2D steady-state saturated flow and reactive transport model to elucidate denitrification patterns in a hillslope aquifer

摘要: In the last 50 years, agricultural intensification has resulted in increasing nutrient losses that threaten health of lakes on volcanic plateau New Zealand's North Island. As part our efforts to understand transport and transformations nitrogen this landscape, 2D vertical groundwater model AquiferSim 2DV was used simulate water flow, nitrate transport, denitrification, discharge surface waters a hillslope adjacent wetland stream discharging into Lake Taupo, Australasia's largest lake. is steady state using finite-difference function method for flow modelling finite-volume mixing cell contaminant modelling. The ratio horizontal hydraulic conductivity must be specified within aquifer domain, as effective porosity denitrification rates. Boundary conditions consist recharge fluxes concentrations, well assumed zone discharge. Hydrodynamic dispersion simulated through numerical dispersion, which depends grid resolution. Denitrification reactions each computational may include both zero-order first-order All parameters spatially heterogeneous. Previous applications have been essentially systems. By contrast, system sloping material layers dynamic table. Extensions were made 2DV, including representation converging/diverging allowed steady-state developed. Comparison predictions with detailed level hydrochemical data from site, however, showed model's attractive simplicity case precluded adequate characterisation what 3D, transient system. While produced reasonable agreement concentration patterns under an average table profile, oxygen concentrations low summer high spring poor. seasonal changes reflected annual pulse fresh, oxidised followed by gradual depletion till next occurs following year, phenomenon could not represented model. This itself provoked fresh thinking about nature chemistry at site.