Science Inventory

Elevated winter stream temperatures below wastewater treatment plants shift reproductive development of Johnny Darter Etheostoma nigrum: a field and histologic approach


Adams, C., D. Winkelman, P. Schaffer, R. Fitzpatrick, J. Cavallin, M. Ellman, K. Santana Rodriguez, AND D. Villeneuve. Elevated winter stream temperatures below wastewater treatment plants shift reproductive development of Johnny Darter Etheostoma nigrum: a field and histologic approach. Fishes. MDPI, Basel, Switzerland, , N/A, (2022).


Reproductive cycles of fish and other aquatic organisms are regulated by environmental variables including photoperiods and water temperatures. In the face of global climate change and urbanization, annual mean river water temperatures are increasing globally. These environmental changes may be outpacing the ability of organisms to evolve and adapt to new environmental cues and synchronize reproductive activity with conditions that maximize reproductive output as well as survival and fitness of their offspring. The present study examined effects of thermal pollution associated with wastewater treatment plant discharges on the timing of reproductive development in the Johnny darter (Ethestoma nigrum), a sentinel fish species native to Colorado. It examines the impact of high over-winter temperatures compared to other reproductive stressors such as endocrine disrupting chemicals and other contaminants. Results indicate that elevated over-winter temperatures are correlated with accelerated reproductive development in this species and was a stronger explanatory variable than other waste-water associated contaminants. The study provides scientific evidence that helps support the value of the state of Colorado’s winter water temperature standards. Additionally, it provides EPA Region 8 and other stakeholders with insights into potential effects of climate change and thermal stresses associated with urbanization on aquatic organisms and the ecosystem services they provide.


Abstract: River water temperatures are increasing globally, particularly in urban systems. In winter, wastewater treatment plant (WWTP) effluent inputs are of particular concern because they increase water temperatures from near freezing to ~7–15?C. Recent laboratory studies suggest that warm overwinter temperatures impact the reproductive timing of some fishes. To evaluate winter water temperature’s influence in the wild, we sampled Johnny Darter Etheostoma nigrum from three urban South Platte tributaries upstream and downstream of WWTP effluent discharge sites. Fish were collected weekly during the spring spawning season of 2021 and reproductive development was determined from histological analysis of the gonads. Winter water temperatures were approximately 5–9?C greater downstream of the WWTP effluent compared to upstream sites, and approximately 2?C warmer at sampling sites ~5,000 m downstream of the effluent discharge. Females collected downstream of WWTP effluent experienced accelerated reproductive development compared to upstream by 1–2 weeks. Water quality, including water estrogenicity, and spring water temperatures did not appear to explain varying reproductive development. It appears that small increases in winter water temperature influence the reproductive timing in E. nigrum. Further investigations into how shifts in reproductive timing influence other population dynamics are warranted.

Record Details:

Product Published Date:11/29/2022
Record Last Revised:12/23/2022
OMB Category:Other
Record ID: 356613