Wastewater reuse may be detrimental to smallmouth bass abundance in the Shenandoah River Watershed
Issue: Municipal and industrial wastewater effluent is an important source of water for streams and rivers, especially during periods of low flow. The reuse of wastewater effluent may become even more important if climate change exacerbates low streamflow and drought conditions. However, wastewater effluent often contains chemicals that, when chronically present, can affect the health of aquatic organisms. Such is the case with the ecologically and socioeconomically important smallmouth bass in the Shenandoah River Watershed, where individuals have shown signs of chemical exposure in unison with mortality events of sexually mature bass. What researchers and managers know less about is how the detrimental effects of chemical exposure on individual fish translate to population-level impacts, which is an important aspect in sustaining the smallmouth bass fishery.
USGS Study
To better understand how chemical exposure from wastewater effluent may be affecting smallmouth bass populations in the Shenandoah River Watershed, USGS investigators addressed two goals. The first was to identify how the percentage of wastewater effluent in streamflow (a proxy for chemical exposure) was related to the abundance of young‐of‐year (YOY), juvenile, and adult bass. The second was determine whether the percentage of wastewater effluent in streamflow better explained patterns in smallmouth bass abundance than streamflow alone.
To conduct the analyses, researchers used smallmouth bass survey data collected by the Virginia Department of Wildlife Resources at 33 sites within the watershed from 1998-2018. Data on wastewater effluent flow were obtained from Discharge Monitoring Report databases compiled by state environmental departments for National Pollutant Discharge Elimination System‐permitted facilities discharging into the Shenandoah River. This effluent data set included 98 wastewater treatment plants (WWTPs), 94 of which were in Virginia. Twenty‐two of these were industrial (i.e., nonpublicly owned treatment works; wastewater derived from manufacturing, mining, and/or refining activities) and 76 were municipal (i.e., publicly owned treatment works; wastewater derived from homes, institutions, and small businesses).
Major Findings
- Wastewater effluent explained patterns in the abundance of young of year smallmouth bass, but not the abundance of juvenile or adult bass. Specifically, young-of-year abundance decreased as the percentage of wastewater effluent in total streamflow increased, resulting in an average 41% predicted decline in abundance for this age class. This relationship was driven by the presence of high percentages of wastewater effluent during the previous year and the prespawn period. Since these are time periods before young-of-year are born, this lagged effect suggests adult fish reproductive performance may have been compromised by chemical exposure when streamflow was comprised of a higher percentage of wastewater effluent.
- There was no evidence that the relationship between bass abundance and the percentage of wastewater effluent was due to a streamflow artifact, as the models incorporating wastewater effluent were better at explaining patterns in bass abundance than the streamflow model that excluded the percentage of effluent.
Management Applications
- Although previous studies exploring the impacts of chemicals linked to wastewater effluent in the Shenandoah River Watershed noted detrimental impacts on individual fish, the current USGS study advances our understanding of how these impacts can influence smallmouth bass at the population level. This is particularly valuable for managing the Watershed’s popular smallmouth bass fishery, as management decisions are based on population-level patterns.
- Although investigations of wild populations are correlative and often lack direct information about the specific mechanisms involved, they provide biologically relevant insight directly pertinent to fish and wildlife management decisions. Furthermore, such studies can facilitate the generation of additional hypotheses that lend themselves to testing under controlled conditions, thereby advancing our insights into the complex suite of biotic and abiotic factors influencing the wellbeing of fish populations.
More Information
- The Effects of Wastewater Reuse on Smallmouth Bass (Micropterus dolomieu) Relative Abundance in the Shenandoah River Watershed, USA. https://setac.onlinelibrary.wiley.com/doi/10.1002/etc.5849
Issue: Municipal and industrial wastewater effluent is an important source of water for streams and rivers, especially during periods of low flow. The reuse of wastewater effluent may become even more important if climate change exacerbates low streamflow and drought conditions. However, wastewater effluent often contains chemicals that, when chronically present, can affect the health of aquatic organisms. Such is the case with the ecologically and socioeconomically important smallmouth bass in the Shenandoah River Watershed, where individuals have shown signs of chemical exposure in unison with mortality events of sexually mature bass. What researchers and managers know less about is how the detrimental effects of chemical exposure on individual fish translate to population-level impacts, which is an important aspect in sustaining the smallmouth bass fishery.
USGS Study
To better understand how chemical exposure from wastewater effluent may be affecting smallmouth bass populations in the Shenandoah River Watershed, USGS investigators addressed two goals. The first was to identify how the percentage of wastewater effluent in streamflow (a proxy for chemical exposure) was related to the abundance of young‐of‐year (YOY), juvenile, and adult bass. The second was determine whether the percentage of wastewater effluent in streamflow better explained patterns in smallmouth bass abundance than streamflow alone.
To conduct the analyses, researchers used smallmouth bass survey data collected by the Virginia Department of Wildlife Resources at 33 sites within the watershed from 1998-2018. Data on wastewater effluent flow were obtained from Discharge Monitoring Report databases compiled by state environmental departments for National Pollutant Discharge Elimination System‐permitted facilities discharging into the Shenandoah River. This effluent data set included 98 wastewater treatment plants (WWTPs), 94 of which were in Virginia. Twenty‐two of these were industrial (i.e., nonpublicly owned treatment works; wastewater derived from manufacturing, mining, and/or refining activities) and 76 were municipal (i.e., publicly owned treatment works; wastewater derived from homes, institutions, and small businesses).
Major Findings
- Wastewater effluent explained patterns in the abundance of young of year smallmouth bass, but not the abundance of juvenile or adult bass. Specifically, young-of-year abundance decreased as the percentage of wastewater effluent in total streamflow increased, resulting in an average 41% predicted decline in abundance for this age class. This relationship was driven by the presence of high percentages of wastewater effluent during the previous year and the prespawn period. Since these are time periods before young-of-year are born, this lagged effect suggests adult fish reproductive performance may have been compromised by chemical exposure when streamflow was comprised of a higher percentage of wastewater effluent.
- There was no evidence that the relationship between bass abundance and the percentage of wastewater effluent was due to a streamflow artifact, as the models incorporating wastewater effluent were better at explaining patterns in bass abundance than the streamflow model that excluded the percentage of effluent.
Management Applications
- Although previous studies exploring the impacts of chemicals linked to wastewater effluent in the Shenandoah River Watershed noted detrimental impacts on individual fish, the current USGS study advances our understanding of how these impacts can influence smallmouth bass at the population level. This is particularly valuable for managing the Watershed’s popular smallmouth bass fishery, as management decisions are based on population-level patterns.
- Although investigations of wild populations are correlative and often lack direct information about the specific mechanisms involved, they provide biologically relevant insight directly pertinent to fish and wildlife management decisions. Furthermore, such studies can facilitate the generation of additional hypotheses that lend themselves to testing under controlled conditions, thereby advancing our insights into the complex suite of biotic and abiotic factors influencing the wellbeing of fish populations.
More Information
- The Effects of Wastewater Reuse on Smallmouth Bass (Micropterus dolomieu) Relative Abundance in the Shenandoah River Watershed, USA. https://setac.onlinelibrary.wiley.com/doi/10.1002/etc.5849