Why the Temperature of Water is Important
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Water temperature affects nearly every other water quality parameter.
Temperature is an important factor to consider when assessing water quality. In addition to its own effects, temperature influences several other parameters and can alter the physical and chemical properties of water. In this regard, water temperature should be accounted for when determining 7:
– Metabolic rates and photosynthesis production
– Compound toxicity
– Dissolved oxygen and other dissolved gas concentrations
– Conductivity and salinity
– Oxidation reduction potential (ORP)
– pH
– Water Density
Water Temperature and Aquatic Life
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The metabolic rates of aquatic organisms increase as the water temperature increases.
Considered alone, water temperature can affect the metabolic rates and biological activity of aquatic organisms14. As such, it influences the chosen habitats of a variety of aquatic life 8. Some organisms, particularly aquatic plants flourish in warmer temperatures, while some fishes such as trout or salmon prefer colder streams 8.
Studies have shown a direct relationship between metabolic rates and water temperature. This occurs as many cellular enzymes are more active at higher temperatures 18. For most fish, a 10°C increase in water temperature will approximately double the rate of physiological function 16. This increase in metabolic rate can be handled by some species better than others. Increased metabolic function can be noticed in respiration rates and digestive responses in most species. Increased respiration rates at higher temperatures lead to increased oxygen consumption, which can be detrimental if rates remain raised for an extended period of time. Furthermore, temperatures above 35°C can begin to denature, or breakdown, enzymes, reducing metabolic function 18.
Temperature fluctuations can also affect the behavior choices of aquatic organisms, such as moving to warmer or cooler water after feeding, predator-prey responses and resting or migrating routines 16. Some species of sharks and stingrays will even seek out warmer waters when pregnant 16.
Temperature affects the photosynthetic rates of different algae.
Temperature affects the photosynthetic rates of different algae.
Plants are also affected by water temperature. While some aquatic plants tolerate cooler waters, most prefer warmer temperatures 17. Tropical plants in particular will show restricted growth and dormancy in water temperatures below 21°C 17. While dormancy is appropriate for surviving a cold winter, warmer temperatures are required for most plants to flourish.
Temperature can also inhibit plant respiration and photosynthesis 14. In general, algal photosynthesis will increase with temperature, though different species will have different peak temperatures for optimum photosynthetic activity 14. Above and below this temperature, photosynthesis will be reduced.
Compound Toxicity and Water Temperature
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Water temperature can play a role in the shift between ammonium and ammonia in water.
In addition to its effects on aquatic organisms, high water temperatures can increase the solubility and thus toxicity of certain compounds 1. These elements include heavy metals such as cadmium, zinc and lead as well as compounds like ammonia 19,20. Water temperature can not only increase the solubility of toxic compounds, but it can also influence an organism’s tolerance limit 19. Mortality rates for zinc are significantly higher at temperatures above 25°C than at temperatures below 20°C 19. This occurs because tissue permeability, metabolic rate and oxygen consumption all increase with increased water temperature 19. In one study on labeo bata fish, the 24 hour 50% lethal concentration (LC50) at 15°C was 540 mg/L, while at 30°C, the LC50 dropped to 210 mg/L 19.
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Dissolved oxygen concentrations are dependent on temperature. The warmer the water, the less oxygen that it can hold.
Ammonia is known for its toxicity at high pH levels, but temperature can also influence acute and chronic criteria concentrations 21. At low temperatures and a neutral pH, the following equation remains shifted to the left, producing the nontoxic ammonium ion:
NH3 + H2O <=> NH4+ + OH-
However, for every 10°C increase in temperature, the ratio of unionized ammonia to ammonium doubles 21. In 2013, the EPA determined that the criterion maximum concentration for freshwater species is 17 mg/L Total-Ammonia-Nitrogen (including both NH3 and NH4+) due to its potential jump in toxicity at a higher pH and temperature 21.
Step-by-step explanation:
