Elevated Winter Stream Temperatures below Wastewater Treatment Plants Shift Reproductive Development of Female Johnny Darter Etheostoma nigrum: A Field and Histologic Approach

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 River tributaries in Colorado 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 5–10 °C greater ~300 m downstream of the WWTP effluent compared to upstream sites, and approximately 3 °C warmer at sampling sites ~5000 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 total 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.

Impact of wastewater treatment plant effluent on the winter thermal regime of two urban Colorado South Platte tributaries

“…Hobo temperature loggers were initially placed at fish sampling locations as part of another project examining temperature impacts on the reproductive development of Johnny Darters (Adams et al, 2022). The naming of these monitoring sites is in relation to their initial position relative to the WWTP effluent, Far upstream (FU), Upstream (U), Downstream (D), and Far downstream (FD), and the river they are located, either the Big Thompson (BT) or the St. Vrain (SV).…”

“…It controls and regulates important biological functions and behaviors including activity, metabolism, development, and reproduction (Brett, 1956;Bestgen & Williams, 1994;Hester & Doyle, 2011). It has been well documented that abnormal thermal regimes resulting from changes in water temperature can alter fish life history processes, reproductive timing, and hatching success (Bestgen and Williams, 1994;Pankhurst and Munday, 2011;Starzynski and Lauer, 2015;Fraser et al, 2019;Adams et al, 2022). Human induced alterations to water temperature have been documented to have negative impacts on fish populations (Farmer et al, 2015;White et al, 2020).…”

“…For example, bluegill sunfish populations in lakes warmed by electrical power plant cooling systems had shorter life spans than those in nearby ambient lakes (White et al, 2020). Increased winter water temperature also affects the reproductive biology of percid fishes (Farmer et al, 2015;Baum, 2021;Adams et al, 2022). This has led federal and state agencies to create river water temperature standards for protection of fishes and river ecosystems.…”

“…Most other predictive modeling efforts have not prioritized other seasons, particularly winter. This is despite considerable documentation that discharge from wastewater treatment plant (WWTP) effluent increases river water temperatures during the winter months (Kinouchi et al, 2007;Rice et al, 2011;Graham et al, 2014), and evidence that abnormally warm winters impact aquatic communities (Farmer et al, 2015;Firkus et al, 2018;Baum, 2021;Adams et al, 2022). Models investigating the magnitude and spatial extent of WWTP effluent on the thermal regime of streams are needed to make efficient management strategies to mitigate thermal impacts in winter and meet local water temperature standards.…”

“…We chose these tributaries for our study because they have low Winter baseflows, experience WWTP effluent discharge, and are of specific conservation concern due to their recreational importance and high concentration of native species (Woodling, 1985). In addition, we have shown that warm effluent can substantially increase winter water temperature and influence the timing of fish reproduction (Adams et al, 2022). Specifically, we hypothesized that air temperature, river discharge, effluent temperature, and distance from the effluent would influence the spatial pattern of water temperature downstream of the WWTP effluent.…”