Why Water Temperature is More Important Than Air Temperature for Ponds

During the scorching summer months we often seek refuge in the ocean to cool off from the blaring heat of the sun.  But when we run into the water we often scream because we are caught off guard at the cold temperature of the water.  This is because water temperature takes a long time heat or cool compared to the air.  This is why it is important for pond owners to go by the water temperature and not air temperature when it comes to caring for your pond.  Water temperature is the determinant for seasonal preparation as well as feeding schedules for your fish or koi. 

Temperature has a major affect on water quality. It influences several factors and can alter the physical and chemical properties of water. Water temperature should be considered when determining metabolic rates and photosynthesis production, toxicity, amount of dissolved oxygen, flow, pH, and density. 

Water temperature wields a major influence on the biological activity and growth of aquatic life. Usually, the rule of thumb is the higher the water temperature, the greater the biological activity. For most fish, a 50°F increase in water temperature will about double the rate of physiological function.  In layman’s terms, the fish will be more active in higher temperatures meaning their bodies will work harder and need more oxygen and food. Oxygen levels are lower in warmer water temperatures, which can pose a problem for all the aquatic life competing for a small amount of oxygen. The amount of dissolved oxygen that a pond can hold is determined by the temperature.  When the water temperature is colder it can hold more dissolved oxygen and aquatic life need less oxygen during this time.  During higher water temperatures, water can hold less dissolved oxygen, which is dangerous because fish are more active and plants require more oxygen to survive.  This is why aeration is important when the hot summer months come and cause the water temperature to rise.

High water temperatures can increase the solubility and thus toxicity of certain compounds. These elements include compounds like ammonia, which can be toxic to aquatic life. Lower water temperatures can have toxicity problems because they affect the flow of water and the potential to freeze. If the water freezes at too low of a temperature, gases get trapped under the ice and can be fatal to plants and fish. Ponds need some way for gas exchange during cold winter months so using a deicer can allow for toxic gases to be released. 

The depth of your pond can determine the temperature of the water as well.  Because light decreases exponentially with depth in the water column, the sun can heat a greater proportion of the water in a shallow pond than in a deep pond and so the shallow pond can warm up faster and to a higher temperature. This is why the air temperature may be cold but the lower layers of water remain warmer.  This serves an important function for the survival of aquatic life during different seasons.  During the winter, warmer layers at the bottom of the pond allow fish and plants to survive the cold weather.  Checking the water temperature often using a thermometer is good to do to make sure the colder water at the top is not hyper-cooling the warmer waters at the bottom. 

Make sure to check your water temperature regularly so you can effectively take care of your pond and keep its habitants happy and healthy.