Temperature

First, water possesses many important thermal qualities. For instance, water has a high specific heat, which means water is not subject to rapid temperature fluctuations because it can absorb or lose large amounts of heat with relatively small changes in temperature. Water temperature changes gradually in response to seasonal changes. Small water bodies will be influenced by air temperature more quickly than larger water bodies.

Temperature determines many physical characteristics of a water body during different seasons of the year. In the winter, water's temperature-dependent density allows aquatic life to survive. Ice is formed at 0 degrees Celsius. Thus, ice will remain at the top of the water body. Sun shining through the ice will serve to warm the water below slightly, keeping the temperature just above freezing. Water at 4 degrees C is the most dense, and will sink to the bottom and be replaced by lighter 1 - 3.9 degrees C water. The continual process of heating and sinking keeps the water body from freezing entirely (Smith, 1990).

In addition, temperate lakes stratify during the summer because of water's temperature-dependent density. Stratification prevents the mixing of oxygen and nutrients in the water body, and often encourages dissolved oxygen depletion (see "Dissolved Oxygen: General Information").

Stratification is a seasonal phenomenon that is the result of the heat of the summer substantially raises the temperature of the upper water layers. As water temperatures increase, the density decreases. Thus, sun-warmed water will remain at the surface of the water body (forming the epilimnion), while the more dense, cooler water settles at the bottom (hypolimnion). The layer of rapid temperature change separating the two layers is called the thermocline (Smith, 1990).

During the spring, stratification will break down allowing mixing of oxygen and nutrients. As spring approaches, the ice melts and the water body achieves a uniform temperature of 4 degrees C. Any slight wind will create currents that mix the nutrients and the oxygen throughout the entire water body (spring overturn).

During the fall, the water body loses heat until the temperature of the water body is uniform at 4 degrees C. Wind creates circulation, which distributes oxygen and nutrients throughout the water body (fall overturn). Eventually, the surface water layer falls below 4 degrees C, becomes less dense, and remains at the surface. Ice will form if temperatures are low enough; otherwise, this upper layer will remain just above 0 degrees C. Deeper water will remain roughly at 4 degrees C until spring (Smith, 1990).

Numerical Categories:

Recommended Thermal Criteria for the U.S. Estuarine Biota:

• Cold Temperated Zone, Atlantic Coast (Long Island, NY, to Cape Hatteras, NC)
  
  Temperatures should not exceed an instantaneous maximum of 30.6 degrees Celsius or a daily mean of 27.8 degrees Celsius (USEPA, 1987).
  
• Warm Temperate Zone, Atlantic and Gulf Coasts (Atlantic coast: Cape Hatteras, NC, to Cape Canaveral, FL; Gulf coast: Tampa, FL to Mexico)
  
  Temperatures should not exceed an instantaneous maximum of 32.2 degrees Celsius or a daily mean of 29.4 degrees Celsius (USEPA, 1987).

EPA has developed an equation to determine maximum weekly average temperatures for growth and survival of fish species. In the 1986 Quality Criteria for Water (EPA 1987) values are calculated for juvenile and adult growth and survival during the summer and maxima during the spawning season for egg survival. Please click on the following fish groups for which you wish to examine more detailed temperature preferences.

Warmwater Bass (e.g., Largemouth) Coldwater Bass (e.g., Striped) Trout Salmon Suckers Crappie or Bluegill Common Carp Northern pike Channel catfish Shellfish

Industrial Effects: Higher temperatures are more effective for coagulation and flocculation processes during raw water treatment. Temperatures below 5 degrees C are especially restrictive (USEPA, 1987).

Environmental Effects: Temperature can exert great control over aquatic communities. If the overall water body temperature of a system is altered, an aquatic community shift can be expected. Many coldwater fish, such as trout and salmon, will disappear as a result of egg and fry mortality, direct adult mortality or reduced reproductive activity, and be replaced by warmwater fish, such as sunfish and cyprinids (e.g., carp, minnows). In water above 30 degrees C, a suppression of all benthic organisms can be expected (James et al., 1979). Also, different plankton groups will flourish under different temperatures. For example, diatoms dominate at 20 - 25 degrees C, green algae dominate at 30 - 35 degrees C, and cyanobacteria dominate above 35 degrees C (USEPA, 1987; Dunne et al., 1978).

In addition, there is potential for physiological distress if a fish swims into a localized warm area of the water. Because of water's high heat capacity, water temperatures do not change rapidly under natural conditions. Thus, fish have not evolved the ability to adapt to rapid temperature fluctuations. As a consequence, undetectable physiological damage occurs when fish are introduced into warmer water. The damage caused is not great enough in itself to cause death; instead, motor functions are impaired that make the fish more susceptible to death via "natural" causes. For example, slowed reflexes may cause a fish to be less successful during natural predator-prey interactions. As a result, the fish may starve or be preyed upon (Kennish, 1992).

Fish that have safely acclimated to the warmer water of a thermal discharge plume are still in danger. If the thermal emission ceases at any time, the resulting rapid water temperature drop may cause fish to die of cold shock. When the emission resumes, the fish may then suffer heat shock. In temperate estuaries, temperature-related fish mortalities are common. Estuarine fish that normally migrate to the ocean in the fall when water temperatures drop may become marooned in a thermal discharge plume over the winter. When emissions cease, the fish are plunged into water colder than their lower lethal limit and most die (Kennish, 1992).

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Higher temperatures often exacerbate low dissolved oxygen level problems in lakes and reservoirs. High temperatures encourage the microbial breakdown of organic matter, a process that requires dissolved oxygen. Unfortunately, warm water naturally holds less dissolved oxygen. Thus, persistent warm conditions may lead to a depletion of dissolved oxygen in the water body (USEPA, 1987).

Temperature often serves as a behavioral cue. Anadromous fish, such as salmon, and shellfish, need temperature minima to trigger reproductive behavior (USEPA, 1987). Higher temperatures can shift the timing of reproduction such that predators are most abundant during the early stages of life. Such mis-timing can cause changes in the community structure. Even a few degrees elevation caused a 50% reduction in the softshell clam fishery in Maine because the predator, the green crab, was not reduced by the natural winter die-off and so increased in population (USEPA, 1987).

Sources:

1. Nonpoint sources: Nonpoint sources include changes in channel or water body size, sediment, reduction in streambank and overstory vegetation, irrigation return flows, irrigation withdrawals, stormwater runoff, low flow, hydromodifications, and unusually hot regional temperatures.
   • Changes in channel or water body size: Water bodies become shallower when the channels are widened or the volume of water is reduced. Temperature will increase because a wider channel has more surface area exposed to the sun's rays.
   • Sediment: The deposition of large quantities of sediment on a lake or river bottom will decrease the channel capacity and force the water to spread out over the banks. A wider channel has more surface area exposed to the sun's rays and temperature will increase.
   • Reduction in streambank and overstory vegetation: Removal of vegetation allows the sun's rays to shine directly into the water. Temperatures will rapidly rise.
   • Irrigation return flows: Irrigation water flowing over hot soil will absorb a large quantity of heat.
   • Irrigation withdrawals: If a large quantity of water is withdrawn for irrigation purposes, the water body may experience a decrease in water volume. Temperatures will rise as a water body becomes shallower.
     
   • Stormwater runoff: Impervious areas, such as parking lots and roof tops, absorb the sun's radiation and retain some of the heat. During a precipitation event, the heat is transferred to the runoff flowing over the impervious surface. This warm water is often discharged directly to a surface water body.
   • Hydromodifications: Hydromodification usually drastically changes the appearance of a water body. If a stream is dammed, the water collects and forms a wide pond. Temperatures will increase because both the surface area and the storage time of the water have increased (the warmed water is not readily washed out of the watershed).
   • Unusually hot regional temperatures (natural source): High temperatures will proportionally increase the surface water body temperature.
   
   
   
2. Point source: The primary point source of temperature pollution is heated effluent from an industry.

Sampling Techniques:

1. Temperature probe

   http://www.noaa.inel.gov/capabilities/smartballoon/

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NCSU Water Quality Group

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