Landscape Disturbance and River Water Quality: Long- and Short-Term Impacts

Abstract

Landscape disturbances, including suburbanization, fire, and conversion of forested land into agriculture, modify watershed soil and vegetation composition, the pathways of water, and ultimately the hydrological and biogeochemical regimes of the system. This consequently varies constituent concentrations and loads transported to nearby surface waters, often degrading water quality over short and long-time scales. In these presentations, we discuss the short and long-term water quality responses to landscape disturbance and how we can potentially mollify resulting water quality degradation.

Estimating long-term water quality response to disturbance is often informed by trend analysis; however, interpreting drivers of trends can be challenging. In the first presentation, we share work to analyze 20-year and 40-year trends in stream temperature, a key indicator of water quality, across 138 sites in the contiguous US. While annual trends indicate mild warming and even cooling in some rivers, we show that these annual trends mask tremendous variability at the monthly timescale. Overall, trends in stream temperatures generally persisted across sites within the same region despite the type and degree of disturbance.

Historic wetland losses, combined with increased land use intensities, have led to higher nutrient levels across multi-scale watersheds. Wetlands outside of floodplains and embedded within uplands are particularly vulnerable to these losses, yet they impart water quality benefits as “biogeochemical powerhouses”. In the second presentation, we demonstrate – via modeling approaches – how wetlands cumulatively affect downstream water quality and the extent to which restoring wetlands works for water quality improvements. While restoring and constructing wetlands can partially offset nitrate reductions downstream, these effects can be short-lived along the stream network and vary in downstream effectiveness based on wetland characteristics.

Bio

Christa Kelleher is an Assistant Professor in the Department of Civil and Environmental Engineering at Lafayette College. She earned her BS degree in Civil and Environmental Engineering from Lafayette, and her MS and PhD from Penn State. Following her time as a postdoctoral scholar at Duke University, she served as an Assistant Professor at Syracuse University, before transitioning back to her alma mater. Her research focuses on understanding the sensitivity of hydrological systems to change and disturbance, especially the impacts of water regulation and urbanization on streamflow and water quality.

Heather Golden is a Research Physical Scientist with the US EPA’s Office of Research and Development in Cincinnati, Ohio. She earned her BS degree in Earth Science at Frostburg State University, Maryland, and her PhD from the State University of New York College of Environmental Science and Forestry in Syracuse. Her research focuses on modeling watershed-scale hydrology and nutrient cycling, particularly focusing on wetlands and headwaters, and the effects of these processes on aquatic ecosystems.