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CADDIS Volume 2: Sources, Stressors & Responses


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Other sources/stressors/responses



Authors: K.G. Sappington, S.B. Norton

Major heat flux processes in streams.  Source: adapted from Moore et al., 2005, and Johnson and Jones, 2000.
Click image to enlarge
Figure 1. Major heat flux processes in streams.
Adapted from Moore et al. (2005) and Johnson and Jones (2000).

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 that influence the movement of heat (Figure 1). In turn, temperature plays a fundamental role in shaping the structure and function of aquatic systems (Table 1), and is frequently used as a basis for classifying streams (e.g., cold-water, warm-water).

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
Simplified conceptual model for temperature
Figure 2. A simple conceptual diagram illustrating causal pathways, from sources to impairments, related to temperature. Click on the diagram to go to the Conceptual Diagrams tab and view a larger version.

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 in the conceptual model for temperature (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 most frequently thought of as the stressor of concern, undesirable effects also can be associated with decreases in temperature, increases in temperature ranges, and increased rates of temperature change.

The checklist below will help you identify key data and information useful for determining 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 sources and activities, site evidence, and biological effects listed in the checklist, click on checklist headings or go to the When to List tab of this module.

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:

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