Temperature Monitoring

Monitoring Thermal Conditions of Watercourses

The collection of stream temperature allows for an enhanced understanding of how the aquatic ecosystem operates, and helps to define both how the stream functions and what fisheries communities exist in a given watercourse. The thermal conditions of watercourses play an important role in maintaining healthy aquatic ecosystems. The thermal conditions of stream influence the overall water quality and the distribution of individual aquatic species, which can range from insects to fish. It is important to understand both the daily and seasonal fluctuation of instream temperatures to fully understand why the stream behaves the way it does. For instance, temperature influences growth rates of fish and determines what habitat many species can use over the course of the year. Different species can have very different thermal tolerances and upper critical limits.

Citizen Scientists performs continuous temperature monitoring at each of its aquatic monitoring stations each summer. Through analysis an understanding of how each watercourse behaves thermally is developed, for instance, low temperature readings can indicate groundwater input. Analysis can also identify problems and opportunities to enhance aquatic ecosystem integrity. Water temperature fluctuations can occur naturally or as a result of anthropogenic perturbations such as thermal pollution (unnatural temperature discharge to watercourses), deforestation of riparian habitat, water withdrawals that reduce water levels, online ponds/reservoirs created by dams/weirs and climate change.  Citizen Scientists looks to identify these conditions over the course of time, in the hope that corrective or preventative action can be undertaken. Ultimately specific management recommendations may need to be developed to address ecosystem conditions.

The analysis conducted can pinpoint thermal issues that exist onsite or as a result of the cumulative effects from upstream activities or conditions. These issues/activities can occur at large scales and/or along long time frames (e.g. associated with multiple dams on a single watercourse) or they can occur at small scales and short and/or on repeating time scales (e.g. associated with short intense rainfalls on hot impervious surfaces). In either case, chronic/long-term or short stochastic thermal conditions or events can have a significant ecological impact on the aquatic ecosystem.

Citizen Scientists currently examines thermal data in two ways. The first is using the method outlined in the Ontario Stream Assessment Protocol (OSAP) (Stanfield, 2005). This is used to calculate the thermal stability of the watercourse at each aquatic monitoring station. The temperature of the stream is logged for the warmest months of the year, at a minimum for the period between July 1st and September 10th, thus temperature loggers are usually deployed for this period of time. The temperatures selected for this first thermal analysis are based on the following points:

•taken after 12:00 pm and as close as possible to 4:00 - 5:00 p.m;

•taken between July 1st and September 10th;

•taken on days when maximum daily air temperature exceeds 24.5ºC; and

•during a heat wave (> two days) and no rainfall to affect baseflow

The stream temperatures are then compared to the maximum air temperature recorded on a data logger that has been setup within the watershed. The calculation for thermal stability is determined through a formula in the OSAP habprogs database that relates the air temperature to the water temperature that occurs at the site under the above noted conditions.

The second method used to examine watercourse thermal condition is one developed by Wehrly, Wiley and Seelbach “A thermal habitat classification for lower Michigan’s rivers” (Werhly et al. 1999). This method establishes thermal stability and thermal habitat conditions based on the fluctuation in every temperature point logged for the first three weeks in July. The result is a thermal stability rating of either: stable, moderately stable or extremely unstable and a thermal habitat rating of either: cold, cool or warm. This method examines more of the data set than the OSAP method, and may be more representative of the actual stream condition. Additionally this examination may more specifically address the level of groundwater input into the watercourse.

Finally the full temperature data set is examined for point-in-time impacts that are not identified by using the other two methods. These point-in-time impacts (stochastic events) are simply events where stream temperature rises or drops very quickly over a short time frame. These point-in-time impacts can have significant impacts on the aquatic ecosystem. If these events become a chronic or a reoccurring condition it can act to shape the aquatic community and eliminate species. Temperature data will be examined over multiple years to determine if changes in the aquatic ecosystem are likely to take place. This understanding will be combined with the information and understanding developed through other monitoring activities to make determinations about aquatic ecosystem condition.

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