A Scale-Aware Modeling Framework to Quantify Subsurface Geochemical Exports and River Water Quality
Abstract
Subsurface geochemical exports of metals and nutrients depend upon bi-directional exchange and concurrent biogeochemical transformation at the terrestrial-aquatic interfaces within a watershed. These processes determine the downstream river water quality. Watershed scale models are required for predictive understanding of river water quality to enable effective water resources management. However, detailed watershed-scale models are computationally expensive and inadequately represent finer-scale heterogeneity; hence, they are likely to misrepresent critical processes. Here we develop a scale-adaptive framework that combines process fidelity with computational tractability for modeling coupled surface- and sub-surface watershed-scale hydro-biogeochemical dynamics. This study aims to predict geochemical exports and river water quality as a function of the characteristic watershed features (e.g., topography and a wetness index) and river landform properties (e.g., meanders, sinuosity, and amplitudes) across spatial scales. To investigate how various characteristic watershed and river landform features influence hydro-biogeochemical dynamics, we developed a biogeochemical reaction network and integrated it into the flow and reactive transport code PFLOTRAN. We carried out three-dimensional reactive flow and transport simulations to describe bi-directional exchange and biogeochemical transformations for a 10-meander system in the lower East River watershed area. This area is located within a high elevation catchment in western Colorado and is characterized by rolling to mountainous topography with multiple river meanders. The three-dimensional model was used to predict subsurface hydrological and biogeochemical fluxes, and simulation results demonstrated that the subsurface export of nitrogen along with organic and inorganic carbon follow the power-law nature of the distribution of sinuosity, amplitudes of meanders, and residence times. However, scaling exponents typical for meanders under oxidizing and reducing conditions are significantly different. Efforts are underway to upscale local subsurface geochemical exports to the larger East River system, by making use, in part, of the high-performance computing platforms provided by PFLOTRAN and the NERSC.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H23B..03D
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0466 Modeling;
- BIOGEOSCIENCES;
- 1828 Groundwater hydraulics;
- HYDROLOGY;
- 1849 Numerical approximations and analysis;
- HYDROLOGY