Preferential flow (PF) is a fundamentally important hydrologic process that influences a variety of earth surficial processes (such as runoff, erosion, nutrient cycling, biogeochemical dynamics, ecological functions, biological activities, gas emission, and contaminant fate). However, PF quantification and prediction remain notoriously elusive. This project seeks to break through this bottleneck by advancing two important fronts: 1) A practical means of detecting and quantifying PF across diverse soil-landscapes, and 2) A new conceptualization of dynamic PF networks embedded in the soil-landscape mosaic. The investigators hypothesize that, while the potential for PF to occur in real-world soils is ubiquitous, it takes the right combination of soils and environments for PF to actually happen. The controls of PF occurrence can be grouped into site factors (e.g., landform unit and soil type) and temporal factors (e.g., initial soil moisture, precipitation characteristics, and plant growth stage). They further hypothesize that a dynamic PF flow network embedded in the subsurface resembles (to some extent) an ephemeral stream-like network, which is governed by a dual-flow regime. The investigators will use large real-time soil moisture monitoring databases to investigate the condition, timing, frequency, and mechanism of PF occurrence in diverse soil-landscapes. High-density and multiple depth soil moisture datasets will be systematically analyzed to identify soil moisture response signatures to precipitation events and to identify various flow scenarios and related mechanisms. A set of tools has been developed to efficiently and consistently analyze soil moisture time series profiles, including the determination and visualization of PF and related controls.
This project addresses a grand challenge in hydrologic sciences, i.e., to develop basic hydrologic principles and tools to further understand flow and transport processes through an irregular and interconnected world. Since hydrology often triggers 'hot spots' and 'hot moments' of biogeochemical reactions and ecological functions, improved detection and quantification of PF also have considerable implications for enhanced determination of chemical fluxes and ecosystem functions. This project will make the completed databases and the toolbox developed freely available to the scientific community. An educational computer program will also be developed to spark interest and appreciation of complex subsurface processes among students and the general public. Graduate and undergraduate education will be an integral part of this project. A panel discussion on Preferential Flow and Fundamental Hydrology will be organized at the AGU and the AAAS annual meetings, and a public webinar on this project's outcomes will also be given.
