Steve is currently a Hydrologist with the Oklahoma-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.
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.
Science and Products
Water quality, sources of nitrate, and chemical loadings in the Geronimo Creek and Plum Creek watersheds, south-central Texas, April 2015–March 2016
New insights into nitrate dynamics in a karst groundwater system gained from in situ high-frequency optical sensor measurements
Compounds of emerging concern in the San Antonio River Basin, Texas, 2011–12
Source, variability, and transformation of nitrate in a regional karst aquifer: Edwards aquifer, central Texas.
Sediment conditions in the San Antonio River Basin downstream from San Antonio, Texas, 2000-13
Characterizing and simulating sediment loads and transport in the lower part of the San Antonio River Basin
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
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
Detections, concentrations, and distributional patterns of compounds of emerging concern in the San Antonio River Basin, Texas, 2011-12
Quality of surface-water runoff in selected streams in the San Antonio segment of the Edwards aquifer recharge zone, Bexar County, Texas, 1997-2012
Science to support the understanding of south Texas surface-water and groundwater resources in a changing landscape
Suspended material availability and filtration-biodeposition processes performed by a native and invasive bivalve species in streams
San Antonio River Sediment and Water Quality Monitoring in an Oil and Gas Production Area
Edwards Aquifer Recharge Zone Surface-water and Groundwater Interaction
Urban Waters Federal Partnership - Edwards Aquifer Recharge Zone Monitoring Network
Edwards Aquifer Studies in Texas
Science and Products
- Publications
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 characterize nitrate concentrations and to document pAuthorsRebecca B. Lambert, Stephen P. Opsahl, MaryLynn MusgroveNew 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 long-term use in groundwater wells. We measured inAuthorsStephen P. Opsahl, MaryLynn Musgrove, Richard N. SlatteryCompounds 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, evaluated the concentrations and distributional pAuthorsRebecca B. Lambert, Stephen P. OpsahlSource, 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. Samples from streams recharging the aquifer, groundwater wells, andAuthorsMaryLynn Musgrove, Stephen P. Opsahl, Barbara Mahler, Chris Herrington, Thomas Sample, John BantaSediment 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 Antonio River Basin downstream from San Antonio, TexaAuthorsDarwin J. Ockerman, J. Ryan Banta, Cassi L. Crow, Stephen P. OpsahlCharacterizing 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 type of suspended sediment can affect the biologicalAuthorsJ. Ryan Banta, Darwin J. Ockerman, Cassi Crow, Stephen P. OpsahlConcentrations 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 fracturing and the produced waters that are a consequence of hyAuthorsStephen P. Opsahl, Cassi L. CrowSediment 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-sediment and bedload samples over a range of hydrologic cAuthorsCassi L. Crow, J. Ryan Banta, Stephen P. OpsahlDetections, 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 a total of 20 sampling sites distributed throughout the San Antonio River Basin,AuthorsStephen P. Opsahl, Rebecca B. LambertQuality 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 aquifer. Samples were collected from four stream basins tAuthorsStephen P. OpsahlScience 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 human-related activities. In south Texas, the NuecesAuthorsDarwin J. Ockerman, Travis J. Garcia, Stephen P. OpsahlSuspended 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 native species. Yet, the feeding preferences of unioAuthorsC.L. Atkinson, M.R. First, A.P. Covich, Stephen P. Opsahl, S.W. Golladay - Science
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-bed...Edwards Aquifer Recharge Zone Surface-water and Groundwater Interaction
The effects of urbanization across the recharge zone in Bexar County and potential impact on the water quality in the Edwards aquifer is a topic of specific concern for the City of San Antonio. The USGS Texas Water Science Center is simultaneously collecting water-quality data from surface-water runoff sites and paired shallow groundwater wells within the recharge zone of the Edwards aquifer to...Urban Waters Federal Partnership - Edwards Aquifer Recharge Zone Monitoring Network
The USGS Texas Water Science Center is implementing a more complete and integrated monitoring network for the Edwards aquifer to improve the understanding of aquifer water quality and establish a baseline for measuring future water-quality changes.Edwards Aquifer Studies in Texas
The Edwards aquifer in south-central Texas is one of the most productive aquifers in the Nation and is the primary source of water for the rapidly growing San Antonio area. Springs issuing from the Edwards aquifer provide habitat for several threatened and endangered species, serve as locations for recreational activities, and supply downstream users.The USGS Texas Water Science Center (TXWSC)... - Multimedia