The metalimnion is bordered on both top and bottom by an edge called the thermocline. The thermocline is defined as the plane of maximum temperature decrease In other words, when the water temperature begins to significantly drop, the thermocline has been crossed. As temperature and density are related, a second cline, known as a pycnocline exists at the same depths. The pycnocline divides water column strata by density Below the second thermocline and pycnocline is the hypolimnion.
This strata is usually too deep to be affected by wind, solar radiation and atmospheric heat exchanges The temperature of the hypolimnion is usually determined by the spring turnover. This temperature may only change minimally, if at all, while stratified Lakes that completely mix at least once per year are known as holomictic lakes There are six types of holomictic lakes, with definitions based on average temperature and how frequently temperatures align These lakes and their dividing factors can be seen in this flow diagram:.
Lakes that do not mix completely are called meromictic lakes These lakes have a lower strata that remains isolated throughout the year. This bottom layer is known as the monimolimnion, and is usually divided from the collective layers above it mixolimnion by a halocline salinity-based cline Meromictic conditions can occur in a holomictic lake when unusual weather conditions cause the lake to stratify before it has time to completely mix Pressure does not directly alter water temperature.
Instead, it shifts the freezing, boiling and maximum density points. The temperature at which boiling and freezing occur will only hold true at sea level 3. This is due to the effect of atmospheric pressure.
At a lower pressure higher altitude , water will boil at a lower temperature. On the other side of the scale, at higher pressures such as in a pressure cooker , water will boil at a higher temperature Atmospheric pressure does not affect the temperature of the water itself, but only its ability to become vapor, thus shifting the boiling to the left or right.
As the hydrostatic pressure increases, the freezing point lowers At high elevations lower pressure , there is a slight increase in the freezing point, but the change in pressure is not enough to significantly affect the point Water temperature can be affected by many ambient conditions. Shallow and surface waters are more easily influenced by these factors than deep water The greatest source of heat transfer to water temperature is from sunlight Sunlight, or solar radiation, is a form of thermal energy The result is a daily fluctuation in water temperature based on the amount of sunlight received by the water.
If a body of water is deep enough to stratify, sunlight will only transfer heat through the photic zone light-reaching. Most of this energy greater than half is absorbed in the first 2 m of the water This energy will continue to be absorbed exponentially until the light is gone.
The photic zone varies in depth but can be up to m deep in the oceans The depth of the photic zone is based on the amount of solids and other light-scattering elements present in the water. The temperature of water below the photic zone is generally only altered when the water is mixed Thus shallower bodies of water tend to warm quicker and reach higher temperatures than deeper water bodies 1.
As heat always flows from a higher temperature to a lower temperature, this transfer can go both ways 6. When the air is cold, warm water will transfer energy to the air and cool off.
If the air is hot, cold water will receive the energy and warm up. The extent of this transfer is based on the thermal inertia and specific heat of water Water temperature fluctuations are more gradual than air temperature fluctuations Increased turbidity will also increase water temperature.
Turbidity is the amount of suspended solids in water. These suspended particles absorb heat from solar radiation more efficiently than water The heat is then transferred from the particles to water molecules, increasing the temperature of the surrounding water Groundwater, streams and rivers can alter the temperature of the body of water into which they flow.
If a spring or groundwater source is colder than the river it flows into, the river will become cooler. Recalling the rules of heat transfer energy flows from hot to cold , the river loses energy to the cooler water as it warms it up 6. If the inflow is large or fast enough, the equilibrium temperature of the water will be close to the temperature of the inflow 1. Glacial fed streams will keep conjoining rivers cooler near the source of the flow than further downstream 1.
Man-made influences on water temperature include thermal pollution, runoff, deforestation and impoundments. Thermal Pollution Thermal pollution is any discharge that will dramatically alter the temperature of a natural water source This pollution commonly comes from municipal or industrial effluents 1. If the temperature of discharge is significantly warmer than the natural water, it can negatively affect water quality. There are several significant consequences of thermal pollution, including diminished dissolved oxygen levels, fish kills and influxes of invasive species Runoff from parking lots and other impervious surfaces are another form of thermal pollution.
Water that flows off of these surfaces absorb much of their heat and transfer it to a nearby stream or river, elevating the temperature 9. Deforestation It is not only manmade additions that can affect water temperature. Water properties: Temperature. Water Science for School. Water properties: Dissolved oxygen.
Water Science for Schools. Recent advances in stream and river temperature research. Hydrological Processes , 22, Caissie, D. The thermal regime of rivers: a review. Freshwater Biology , 51, Potential impacts of changing temperatures on water quality and mahinga kai Decreases in available oxygen DO with increasing temperatures - reduces oxygen available for mahinga kai.
Increases in fish metabolic rates - sudden changes, like those found at a discharge points, are more likely to cause stress and possibly death. Increases in algal abundance and changes in the dominant species present - as the water gets warmer algal growth increases, often resulting in algae blooms.
Changes in the amount and type of animals present - some animals cannot tolerate extreme changes in temperature and will avoid these areas habitats of a waterway if unfavourable. Changes in migration patterns - water temperature triggers the time of migration for breeding as mahinga kai travel to and from the sea. Changes in water temperature and flow throughout streams or rivers or at localised points can have significant impacts on movement of fish through the water column deep and shallow.
Water temperature and geothermal. What are the impacts of geothermal energy generation activities on water temperatures? Dissolved oxygen comes from the atmosphere and from photosynthesis by aquatic plants, and is depleted through chemical oxidation and respiration by aquatic animals and microorganisms, especially during the decomposition of plant biomass and other organic material. Surface water, near the water-atmosphere interface and with sufficient light for photosynthesis, is generally saturated or even supersaturated with oxygen.
Deeper water receives oxygen through mixing by wind, currents, and inflows. Mixing and aeration also occur at waterfalls and rapids. Dissolved oxygen can be reduced to very low levels during the winter months when water is trapped under ice.
Dissolved oxygen is essential for a healthy aquatic ecosystem. Fish and aquatic animals need the oxygen dissolved in the water to survive. The need for oxygen depends on the species and life stage; some organisms are adapted to lower oxygen conditions, while others require higher concentrations.
Dissolved oxygen can affect the solubility and availability of nutrients, which can be released from sediments under conditions of low dissolved oxygen B. MELP et al.
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