Relationship Between Water Temperatures and Air Temperatures for Central U.S. Streams
Water temperature in lakes is governed by a com- plex heat budget, where the . tonic relationship between air temperature and surface wa-. Air and Illinois River water temperature data at Peoria and Havana, The water- air temperature relationship was found to be essentially a stationary linear. 50% of the Sun's energy is absorbed by the Earth and then released back into the atmosphere. Thus, the temperature of the air in a given location can be greatly.
These salts and minerals enter the water from rocks and sediment in contact with it. As they dissolve and the ionic concentration increases, so will the conductivity of water.
Many salts are more soluble at higher temperatures. The rate at which conductivity increases is dependent on the salts present in solution In addition, there are a few salts that become less soluble at warmer temperatures, and thus will negatively affect conductivity The effect that temperature has on ORP values depends on the chemical species atoms, molecules and ions present in the solution Temperature-dependence data charts are usually available for calibration solutions, but not for field samples This lack of data is due to the difficulty in identifying and measuring every redoxing species that could be present in any given water source.
As these species are difficult to know and quantitatively define in environmental studies, most ORP electrodes will not automatically compensate for temperature.
However, temperature can still alter a reading and should be recorded with each measurement considered when analyzing the data At a pH of 7, the hydrogen and hydroxyl ions have equal concentrations, 1 x M, keeping the solution neutral As the temperature increases or decreases, the ion concentrations will also shift, thus shifting the pH value Any change to a system at equilibrium, such as adding a reactant or altering the temperature, will shift the system until it reaches equilibrium again That means if the temperature of water increases, the equation will shift to the left to reach equilibrium again.
A shift to the left decreases the ions in water, increasing the pH. Likewise, if the temperature were to decrease, the equation would shift to the right, increasing the ionic concentration and decreasing pH. The pH of pure water varies with temperature while remaining perfectly neutral. Pure water only has a pH of 7.
However, that does not mean that temperature changes will make a solution more acidic or basic. Because the ratio of hydrogen and hydroxyl ions remains the same, the acidity of water does not change with temperature Instead, the entire pH range shifts, so that neutral water will have a value other than 7.
Density and Water Temperature Water temperature and water density are directly related. As the temperature of water increases or decreases, it will alter the density of water. This is why ice expands and floats on water. Pure water is also unique in that it achieves its maximum density, 1.
Icebergs are an extreme example of how ice floats on top of water. Water freezes from the surface down, allowing organisms to survive the winter below the ice cover.
- Water Temperature
The maximum density point is particularly important in freshwater. As surface water temperature approaches the maximum density temperature, it sinks and is replaced by warmer, lighter water This process continues until the water is uniformly cool. Any water that is colder than this point will float on top of the denser water. This process occurs seasonally in holomictic mixing lakes, as the water temperature and thus other parameters reach equilibrium Saltwater Temperature Points Freezing point and maximum density decrease as salinity levels increase.
It is important to note that salinity not only affects water density but it can shift the maximum density and freezing points of water. As the salt concentration increases, both maximum density and the freezing point will decrease Average seawater has a salinity level of 35 PPT parts per thousand and has a shifted maximum density of However, this maximum density is never reached Instead, the process on convection simply circulates the cooling water until the entire surface water column reaches the freezing point As the phase boundary between liquid and solid requires the proper pressure as well as temperature, ice only beings to form on the surface The coldest recorded natural seawater temperature was Likewise, the coldest ocean currents recorded were In both cases, hydrostatic pressures allowed water to remain liquid at such cold temperatures Salt water, however, has a lower freezing point.
That is why salt is used in winter to de-ice roads and sidewalks. Average seawater has a salinity level of 35 PPT parts per thousandwhich shifts the freezing point to Ice floats on top of the denser water.
That does not sound like a large difference, but it is enough to keep ice floating on top of water and allows aquatic organisms to survive the winter. This drop in density occurs because the hydrogen bonds in water create an open hexagonal lattice, leaving space between the molecules Ice formed in seawater is even less dense than freshwater ice When saltwater begins to freeze, the water molecules begin to form a crystal lattice just like they do in freshwater.
These crystals only include water molecules, not salt ions, and the formation is known as brine exclusion As the ice structure grows, pockets of concentrated saltwater can be trapped inside the ice, but are not incorporated into its structure. The trapped water can eventually drain, leaving a small air bubble in the ice. The air bubbles left behind reduce ice density significantly — down to 0.
Land and Water Affect Temperature
Multiyear ice in Antarctica is fresher than new sea ice. Older ice structures, called multiyear ice, have no brine left and are fresh enough to drink once melted The lake mixes every spring and fall, realigning the temperature throughout the lake.Temperature and Density
The thermocline exists at different depths depending on the season. Stratification is the division of a water column into strata, or layers, of water with different properties. These divisions are usually defined by temperature and density, though other parameters such as salinity and chemical distinctions can also be used Stratification occurs because work force and displacement is required to mix liquids of different densities As seasons progress, sunlight, wind, ambient temperature and ice in winter cause the lake to restratify Lake stratification — the different layers are separated by thermoclines, or temperature gradients.
When referring to temperature and density strata within a lake, the layers are usually called the epilimnion, metalimnion and hypolimnion from top to bottom The upper layer, the epilimnion, is exposed to solar radiation and thermal contact with the atmosphere, keeping it warmer.
Can air temperature be used to project influences of climate change on stream temperature?
The epilimnion will extend as far as sunlight and wind will allow, and is usually deeper in lakes with greater surface areas Below the epilimnion is a layer of water with a rapidly changing temperature range known as the metalimnion The metalimnion serves as the boundary between the upper and lower layers of water. The temperature in this strata can vary greatly between its top and bottom depths In addition, the metalimnion can fluctuate in thickness and depth due to weather conditions and seasonal changes 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 and Water Temperature Points 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. Pressure can change the boiling point of water.
The Relationship Between Air Temperature and Stream Temperature
This is due to the effect of atmospheric pressure. At a lower pressure higher altitudewater will boil at a lower temperature. On the other side of the scale, at higher pressures such as in a pressure cookerwater 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 pressurethere is a slight increase in the freezing point, but the change in pressure is not enough to significantly affect the point What Factors Influence Water Temperature?
Water temperature can be affected by many ambient conditions. Shallow and surface waters are more easily influenced by these factors than deep water Sunlight 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.
Solar radiation is the greatest influence on water temperature. 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.
Atmosphere Rivers can appear to steam in winter when colder air flows over the warmer water. 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 Turbidity Turbidity monitoring during the Passaic river dredge project. Turbidity can increase water temperatures. 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 Confluence As the river flows into the lake, it can affect the temperature of the water.
Roberto Araya Barckhahn via Wikimedia Commons Groundwater, streams and rivers can alter the temperature of the body of water into which they flow.
Water Temperature - Environmental Measurement Systems
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 coldthe 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. Third, due to thermal inertia, stream temperature does not respond instantaneously to changes in air temperature.
Including lags in air temperature effects can improve estimates for models with short time scales Benyahya et al. Fourth, while the amount of stream temperature data available worldwide is increasing very rapidly Webb et al. Very few study regions have a complete matrix of sample sites and years: Incomplete within-year data will have variable effects on estimation depending on the extent and timing of the missing data.
Effects of missing data will also depend on model type. For simple linear models, within-year missing data may not have a large effect on estimation because of the linear relationship between stream and air temperature.
Fifth, spatial and temporal autocorrelation can cause estimation problems Caissie, ; Benyahya et al. Autocorrelation occurs when data points in space or time are not independent, i. Finally, air temperature is not the only important predictor of stream temperature Webb, ; Caissie, Many regression-based models have evaluated effects of landscape and environmental drivers on stream temperatures Hawkins et al. Here, we develop a model for mean daily stream temperature that improves accuracy of statistical models by addressing most of the issues listed above.
To avoid fitting a relationship between stream and air temperature when there is none e. This metric is flexible among years and sites. To address hysteresis, we estimate a non-symmetrical trend across the synchronized days with a hierarchical structure to accommodate missing data. We also add an autoregressive term to the model to deal with temporal autocorrelation and we estimate spatial covariance to accommodate spatial autocorrelation.
Because data presented here are spatially constrained to four sites in a small network, we do not include landscape variables in the model. The two environmental drivers in the model are air temperature and stream flow.
In addition to presenting the model, we analyze trends in estimates over time and conduct a detailed missing observations analysis. A dense canopy of mixed hardwood with some hemlocks provides cover throughout the watershed.