We work at the interface of energy, water, and environment.
Our team focuses on a range of topics where hydrological and biogeochemical coupling between flow, transport, and reaction processes play a key role in determining water composition. We work around a couple of major themes.
Developing predictive understanding of hydrobiogeochemical coupling at the watershed scale
Watersheds are the fundamental earth surface units that support river networks, the blood vessels of Earth’s skin. Watersheds partition water, mass, and energy into distinct compartments (atmosphere, trees, soil, groundwater aquifers) through a complex suite of hydrobiogeochemical processes that mobilize key elements (e.g., C, N, P, metals) into rivers, the fluxes of which govern water quality and support aquatic ecosystems downstream. These hydrobiogeochemical interactions are tightly and nonlinearly coupled through thermodynamic and kinetic laws of physics, chemistry, and biology. Watersheds are Earth’s hydrobiogeochemical complex systems that respond and adapt to changes in external forcings, maintaining a clement environment for life on Earth. These complex processes also govern contaminant spreading from non-point sources and regulate natural water quality and quantity. The Li group has recently developed modeling capabilities (RT-Flux-PIHM) that have enabled us to understand and predict such complex process coupling in pristine and human-impacted watersheds. Two projects are ongoing in this theme.
1. Predictive Understanding of Metal Export from Coal Creek, Colorado
Coal Creek watershed (CO) is a high elevation watershed that are affected by historical mining activities. Coal Creek provides the drinking water resources for the town of Crested Butte, CO. Preliminary data at the site have indicated strong connections between metals such as Cd and Zn and dissolved organic carbon (DOC). Most metal export occurs during the high flow – spring melt period when DOC concentrations are highest. This project is set to develop predictive understanding of hydrology-driven soil carbon decomposition. Such understanding and predictive capabilities are important not only for Coal Creek, CO, but also for other human-impacted watersheds including those in Appalachian Basin that extends thousands of miles. Human activities including historical mining and current natural gas production have threatened water resources that are important for tens of million people. Predicting capabilities are also essential in understanding the responses of these contaminated watersheds to changing climate. We acknowledge the support by the Department of Energy Subsurface Biogeochemistry Research Program.
2. Using the Susquehanna – Shale Hills CZO to Project from the Geological Past to the Anthropocene Future
This project is part of the Critical Zone Observatory (CZO) program supported by NSF. Our goal in this project is to understand watershed hydrogeochemical process coupling and how such coupling controls the export and the loads of chemicals that enter aquatic systems. These chemicals include non-reactive tracer, geogenic species derived from chemical weathering, and biogeochemical relevant species such as organic C and nutrients (N, P). Predictive understanding gained here are important to project the response of watersheds to external perturbation, including contamination events, and external forcings, including the changing climate.
Reactive transport in the natural subsurface
Nature is ubiquitously heterogeneous. Preferential flow path, macro pores, and low-permeability clay-rich zones abound in nature. The spatial distribution patterns of these physical (water-conductive) and chemical (reactive) characteristics determine the interactions among water, rock, and biological components (e.g., bacteria, fungi, roots), as well as the natural attenuation and remediation of contaminants. Understanding the role of spatial heterogeneities in solute reactive transport in the subsurface remains a central theme for the Li reactive transport group. We have published work on the role of spatial heterogeneities in affecting:
1. Contaminant bioremediation
(see Li et al., 2009, 2010, 2011, and Bao et al., 2014 in publication page)
2. Reactive Transport of contaminants from Marcellus Shale waters
(see Cai and Li, 2017, and Cai and Li, in preparation)
3. Critical reactive Interfaces during Water-rock interactions
(see Salehikhoo et al., 2013, 2014; Salehikhoo and Li, 2015; Wen and Li, 2017)