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CADDIS Volume 2

Temperature

Major heat flux processes in streams.Figure 1. Major heat flux processes in streams. Click diagram to view a larger version.
Adapted from Moore et al. (2005) and Johnson and Jones (2000)

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Temperature is the concentration of thermal energy in a substance such as water. The phrase "thermal regime" is used when emphasizing the temporal and spatial distribution of temperature.

Temperatures in streams and rivers are influenced by many atmospheric and hydrologic processes affecting the movement of heat (see Figure 1). In turn, temperature plays a fundamental role in shaping the structure and function of aquatic systems (see Table 1). It is frequently used as a basis for classifying streams (e.g., coldwater, warmwater).

This module provides advice for deciding whether to include temperature in your list of candidate causes. You may go directly to a specific section of interest by clicking on the tabs above.

Table 1. Example Attributes of Aquatic Ecosystems Affected by Temperature
Category Example Attributes
Physical Water density, thermal stratification, solubility of oxygen and other chemicals
Chemical Rates of nutrient cycling, contaminant transformation rates
Biological Organism survival, growth, reproduction, development, behavior, habitat preference, competition

Checklist of Sources, Site Evidence and Biological Effects

Temperature should be listed as a candidate cause when potential or observed human source and activities, site observations or observed effects support portions of the source-to-impairment pathways (see Figure 2). The more the thermal regime departs from the natural regime, the more likely it is to cause undesirable biological effects. Although increased temperature is more often a stressor of concern, impairment also can result from decreased temperatures, increased temperature ranges, and increased rates of temperature change.

The checklist below will help you identify whether to include temperature among your candidate causes. The list is intended to guide you in collecting evidence to support, weaken or eliminate temperature alteration as a candidate cause. For more information on specific entries, go to the When to List tab.

A simple conceptual diagram illustrating causal pathways, from sources to impairments, related to temperature. Figure 2. A simple conceptual diagram illustrating causal pathways, from sources to impairments, related to temperature. Click on the diagram to view a larger version.Consider listing temperature as a candidate cause when the following sources and activities, site evidence and biological effects are present:

Sources and Activities

  • Discharge of heated effluents
  • Removal of riparian vegetation
  • Removal of upland vegetation
  • Impervious surfaces
  • Channel alteration
  • Impoundments or dams
  • Removal of water from surface or groundwater

Site Evidence

  • Reduced riparian cover
  • Temperature measurements

Biological Effects

  • Absence of coldwater taxa where they are expected
  • Absence of warmwater taxa where they are expected
  • Congregation of fish near heated discharges
  • Congregation of coldwater fish near ground inputs
Consider contributing, modifying and related factors as candidate causes when selecting temperature as a candidate cause:
  • Dissolved oxygen
  • Ionic strength
  • Flow alteration
  • Sediments
  • Ammonia

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