Dr. Mike O'Driscoll | Current Research
Over the last century, changes in land-use, climate, and population have caused a decline in the availability of clean, fresh water. Associated habitat impairments have altered aquatic ecosystems and diminished valuable ecological services such as filtration and floodwater storage. There is a growing need to quantify eco-hydrological processes to understand how watersheds function and respond to changing land-use and climate. My work focuses on two important aspects of hydrology: 1) surface water-groundwater interactions and 2) nutrient cycling. My goal is to answer the questions: What factors regulate groundwater and nutrients in surface waters and how are hydrological processes altered by anthropogenic disturbances? I use an interdisciplinary approach, capitalizing on hydrogeological, geochemical, geophysical, ecological, and modeling techniques. Ultimately, I seek to advance the understanding of how surface waters interact with groundwater and quantify the signature of human activity on hydrological processes. My recent research has focused on understanding how anthropogenic disturbances affect streamflow processes and non-point source nutrient inputs to shallow aquifers and surface waters. Anthropogenic disturbances to the surficial aquifer (e.g. urbanization) are becoming increasingly important because of their influence on the quality and quantity of groundwater inputs to surface waters.
Like many regions, the southern United States is rapidly urbanizing. While numerous investigations have focused on the effects of urbanization on hydrological processes in the Piedmont settings of the southern United States, significantly less research has been published on the hydrological response to urbanization in the southeastern Coastal Plain. In a recent study, we found that riparian groundwater levels were inversely related to the degree of urbanization (catchment total impervious area (TIA)). As urbanization, TIA, and stormwater runoff increased, the degree of stream channel incision increased and riparian ground-water tables declined, resulting in a shift to drier conditions in the urban riparian zones (“urban riparian hydrologic drought”) (Hardison et al. 2009, Journal of the American Water Resources Association). This study is currently being used by the US EPA on their Causal Analysis/Diagnosis Decision Information System (CADDIS) website to assess aquatic systems.
Land-use changes have also increased nutrient inputs to surface waters in the southeastern Coastal Plain. Excess nutrients have contributed to eutrophication of fresh water and estuarine systems and harmful ecological effects, such as algal blooms and fish kills. Groundwater contributions of nutrients to streams are often difficult to measure, and consequently, are often overlooked. In our current efforts, we have focused on quantifying groundwater nutrient exports from on-site wastewater systems (septic systems). In coastal North Carolina 60% of residences use these systems, but the amount of wastewater nutrients and pathogens transported to surface waters is not well-constrained. Currently, we are testing geophysical approaches (electrical resistivity, ground penetrating radar, and electromagnetic induction) to characterize subsurface wastewater plumes in sensitive coastal watersheds. This work has been funded by the Centers for Disease Control and Prevention (see figure below), the North Carolina Water Resources Research Institute, and the North Carolina Department of Environment and Natural Resources.
Figure (below): This figure shows the groundwater transport of nitrogen from a septic system to the Pamlico River Estuary. Groundwater monitoring was conducted at this coastal residence during a 2-year study funded by the Centers for Disease Control and Prevention.