Stephen Opsahl
Biography
Steve’s interest in science began at an early age and he could usually be found around water. Steve received a bachelor’s degree in microbiology from the University of Texas at Austin and followed this with a Ph.D. in Marine Science from the U.T. Austin Marine Science Institute in Port Aransas, TX. Steve’s research focuses on natural and anthropogenic tracers in aquatic systems and the influence of UV radiation on both biology and chemistry. While in Georgia, Steve developed an appreciation for aquifers including their importance as an ecosystem and for supporting human life. Steve is currently a Hydrologist with the Texas Water Science Center in San Antonio and intends to apply his experiences to help better understand and manage the aquatic network of Texas including watersheds, aquifers, and coastal marine systems.
Science and Products
San Antonio River Sediment and Water Quality Monitoring in an Oil and Gas Production Area
During 2011-2013, baseline concentrations of many different water and streambed-sediment constituents were determined at Phase I sites upstream from, within, and downstream from the area of active oil and natural-gas production within the San Antonio River Basin. With baseline conditions previously established, this study will provide current information that couples recent water and stream-...
Water quality, sources of nitrate, and chemical loadings in the Geronimo Creek and Plum Creek watersheds, south-central Texas, April 2015–March 2016
Located in south-central Texas, the Geronimo Creek and Plum Creek watersheds have long been characterized by elevated nitrate concentrations. From April 2015 through March 2016, an assessment was done by the U.S. Geological Survey, in cooperation with the Guadalupe-Blanco River Authority and the Texas State Soil and Water Conservation Board, to...
Lambert, Rebecca B.; Opsahl, Stephen P.; Musgrove, MaryLynn
New insights into nitrate dynamics in a karst groundwater system gained from in situ high-frequency optical sensor measurements
Understanding nitrate dynamics in groundwater systems as a function of climatic conditions, especially during contrasting patterns of drought and wet cycles, is limited by a lack of temporal and spatial data. Nitrate sensors have the capability for making accurate, high-frequency measurements of nitrate in situ, but have not yet been evaluated for...
Opsahl, Stephen P.; Musgrove, MaryLynn; Slattery, Richard N.
Compounds of emerging concern in the San Antonio River Basin, Texas, 2011–12
The City of San Antonio and the surrounding municipalities in Bexar County, Texas, are among the fastest growing cities in the Nation. Increases in residential and commercial development are changing runoff patterns and likely will increase chemical loads into streams. The U.S. Geological Survey, in cooperation with the San Antonio River Authority...
Lambert, Rebecca B.; Opsahl, Stephen P. Source, variability, and transformation of nitrate in a regional karst aquifer: Edwards aquifer, central Texas.
Many karst regions are undergoing rapid population growth and expansion of urban land accompanied by increases in wastewater generation and changing patterns of nitrate (NO3−) loading to surface and groundwater. We investigate variability and sources of NO3− in a regional karst aquifer system, the Edwards aquifer of central Texas...
Musgrove, MaryLynn; Opsahl, Stephen P.; Mahler, Barbara J.; Herrington, Chris; Sample, Thomas; Banta, John
Sediment conditions in the San Antonio River Basin downstream from San Antonio, Texas, 2000-13
Sediment plays an important role in the ecological health of rivers and estuaries and consequently is an important issue for water-resource managers. To better understand sediment characteristics in the San Antonio River Basin, the U.S. Geological Survey, in cooperation with the San Antonio River Authority, completed a two-part study in the San...
Ockerman, Darwin J.; Banta, J. Ryan; Crow, Cassi L.; Opsahl, Stephen P. Characterizing and simulating sediment loads and transport in the lower part of the San Antonio River Basin
This extended abstract is based on the U.S. Geological Survey Scientific Investigations Reports by Crow et al. (2013) and Banta and Ockerman (2014). Suspended sediment in rivers and streams can play an important role in ecological health of rivers and estuaries and consequently is an important issue for water-resource managers. The quantity and...
Banta, J. Ryan; Ockerman, Darwin J.; Crow, Cassi; Opsahl, Stephen P.
Concentrations of selected constituents in surface-water and streambed-sediment samples collected from streams in and near an area of oil and natural-gas development, south-central Texas, 2011-13
During 2011–13, the U.S. Geological Survey, in cooperation with the San Antonio River Authority and the Guadalupe-Blanco River Authority, analyzed surface-water and streambed-sediment samples collected from 10 sites in the San Antonio River Basin to provide data for a broad range of constituents that might be associated with hydraulic...
Opsahl, Stephen P.; Crow, Cassi L.
Sediment characteristics in the San Antonio River Basin downstream from San Antonio, Texas, and at a site on the Guadalupe River downstream from the San Antonio River Basin, 1966-2013
San Antonio and surrounding municipalities in Bexar County, Texas, are in a rapidly urbanizing region in the San Antonio River Basin. The U.S. Geological Survey, in cooperation with the San Antonio River Authority and the Texas Water Development Board, compiled historical sediment data collected between 1996 and 2004 and collected suspended-...
Crow, Cassi L.; Banta, J. Ryan; Opsahl, Stephen P.
Detections, concentrations, and distributional patterns of compounds of emerging concern in the San Antonio River Basin, Texas, 2011-12
During 2011–12, the U.S. Geological Survey, in cooperation with the San Antonio River Authority, evaluated detections, concentrations, and distributional patterns of selected compounds of emerging concern (hereinafter referred to as “CECs”) from water-quality samples (hereinafter referred to as “samples”) collected at...
Opsahl, Stephen P.; Lambert, Rebecca B.
Quality of surface-water runoff in selected streams in the San Antonio segment of the Edwards aquifer recharge zone, Bexar County, Texas, 1997-2012
During 1997–2012, the U.S. Geological Survey, in cooperation with the San Antonio Water System, collected and analyzed water-quality constituents in surface-water runoff from five ephemeral stream sites near San Antonio in northern Bexar County, Texas. The data were collected to assess the quality of surface water that recharges the Edwards...
Opsahl, Stephen P.
Science to support the understanding of south Texas surface-water and groundwater resources in a changing landscape
Against a backdrop of constant cycles of extreme hydrologic conditions ranging from oppressive droughts to life-threatening floods, the water-resource landscape of south Texas is undergoing constant change. Demands on water resources are increasing because of changes related to population growth, energy demands, agricultural practices, and other...
Ockerman, Darwin J.; Garcia, Travis J.; Opsahl, Stephen P. Suspended material availability and filtration-biodeposition processes performed by a native and invasive bivalve species in streams
Unionid mussels are among the most threatened group of freshwater organisms globally. They are known for their ability to filter food particles from flowing and standing waters. However, invasive bivalve species, such as the Asian clam (Corbicula fluminea) in North America, have the potential to overlap in feeding and potentially out-compete the...
Atkinson, C.L.; First, M.R.; Covich, A.P.; Opsahl, S.P.; Golladay, S.W.