Cooperative Fish and Wildlife Research Units Program: Colorado
Education, Research and Technical Assistance for Managing Our Natural Resources

Colorado Project

Field examination of thermal pollution on stream temperature and reproductive development of Johnny Darter, Etheostoma nigrum (Percidae)

May 2021 - April 2022


Participating Agencies

  • Colorado Parks and Wildlife
  • Colorado Parks & Wildlife
  • Colorado Parks & Wildlife
  • CO Division of Parks and Wildlife
  • City of Longmont

Project Description:

Objective 1. Characterizing Wastewater Effluent Water Temperatures

Goal: To characterize WWTP effluent and its effect on stream thermal characteristics.

Background: Wastewater effluents (WWE) will have varying influences on stream temperature depending on the temperature of the effluent and the discharge and temperature of the receiving stream. The effects of WWE will also vary seasonally based on water temperature and discharge. We propose to monitor temperature from sites that characterize various effluent scenarios as a baseline for interpreting biological data (See Objective 2 below). These data will also serve as a temperature baseline for future monitoring and management of eastern Colorado transitional and warm water streams.


Task 1. We propose to meet with managers and scientists from Colorado Parks and Wildlife, other interested agencies, and WWTPs to determine appropriate field sites for monitoring temperature. Once sites are identified, we will deploy temperature-monitoring equipment. We will also and monitor stream discharge and basic water quality seasonally at the same sites. Stream discharge will be measured using standard USGS methods. Basic water quality data will include specific conductance, pH, water temperature, turbidity, and dissolved oxygen. We also propose to gather, collate, and summarize existing historical records for temperature from WWTP’s and other groups that monitor temperature on eastern Colorado transitional and warm water streams.

Task2. To understand the influence of WWTP effluent on stream temperature it is important to consider the longitudinal aspects of water temperature (Figure 1). VerHoef and Peterson’s (2010) spatial statistical network models are a well-recognized tool for analyzing stream attributes like temperature. The GIS tools and R script for implementing these models are available and have been used extensively in temperature modeling (Issak et al. 2014 and We propose to analyze data collected in Task 1 using these models.

Figure 1. Conceptual model of stream temperature measurement and modeling. The x-axis represents distance to and from a WWTP. The hashes on the x-axis represent locations of temperature monitors. The dashed line represents a temperature threshold and this could represent an important temperature for any biological activity (i.e. reproduction). The WWTP effluent raises the base stream temperature. In this example, the temperature decreases exponentially back to the base stream temperature. However, the relationship of stream temperature to distance downstream could be any function. In this example, the stream temperature returns to the threshold between two temperature monitors. If the function is known, then the spatial location of the event can be identified, as well as the uncertainty of that location. The same modeling can be done with other events, such as return to base temperature. Covariates that effect the shape of the function can also be included (i.e. air temperature, discharge, land cover).

Objective 2. Evaluating Johnny Darter reproduction in the field

Goal: To evaluate reproductive condition of Johnny Darter in the wild.

Background: Gonad weight changes seasonally and can indicate reproductive status in fishes. However, inferences that are more detailed can be made using histology and histology is an effective tool to study the reproductive cycle in fishes (Blazer 2002). It is routinely used for sex verification and assessing reproductive development (Blazer 2002). It can also be used to document abnormalities, such as intersex, and diseases, such as tumors and parasites (Blazer 2002). Gonadal histology can provide insights into reproductive timing as well as the effects of various environmental stressors on reproductive health (Blazer 2002).

Approach: We will evaluate reproductive condition using gonad weights and histology. The general strategy will be to collect Johnny Darter seasonally from above and below WWTP’s at the sites identified in Goal 1-Task 1. We will compare fish reproductive status among sites and correlate those observations with water temperature.