Freshwaters surface water temperature

Evaporation and Evaporative Fractionation of Water. Evaporation from standing water bodies is the principal fractionation mechanism in most hydrological systems. Evaporative isotopic enrichment is a function of numerous factors (e.g., temperature, salinity, and relative humidity) that cause considerable variation in the lsO/ ieO and D/H ratios of natural surface waters. Craig and Gordon (22) evaluated isotopic effects on precipitation and evaporation in the ocean-atmosphere system. Much of what was developed in that work is directly applicable to the freshwater systems discussed here. 

Before discussing in detail any of the fate and transport processes occurring in surface waters, the major characteristics of surface waters must be defined. As illustrated in Fig. 2-1, rivers and streams are relatively long, shallow, narrow water bodies characterized by a pronounced horizontal movement of water in the downstream direction. Often the water flow is sufficiently turbulent to erode the stream channel and carry sediment for considerable distances. Due to this movement of sediment, some river channels are constantly shifting in geometry. Compared with rivers, lakes tend to be deeper and wider and are not dominated by a persistent downstream current (Fig. 2-2). Lakes are often vertically stratified for part of the year, with two distinct layers of water whose temperatures and chemistries are markedly different. Estuaries (Fig. 2-3), the interfaces between rivers and the ocean, also are often vertically stratified, due to the denser saline seawater sinking beneath the freshwater discharged from the river. Estuaries have tides due to their connection to the ocean, and they tend to be rich in nutrients. 

Stratification in estuaries is in some respects similar to stratification in lakes, although in estuaries the density difference is primarily due to the difference in salinity between freshwater and ocean water, instead of being primarily due to temperature differences, as in most lakes. Freshwater has a density of approximately 1.00 g/cm3, whereas ocean water has a density of approximately 1.03 g/cm3 due to dissolved salts [primarily sodium (Na+), chloride (Cl-), calcium (Ca2+), and sulfate (SO4 ). This is a much larger density difference than that which occurs due to temperature differences in surface waters hence, the stratification may be very strong. Whatever its cause, stratification always inhibits the vertical transfer of dissolved chemicals from layer to layer. 

Deuterium contents of seawaters from major oceans, rivers, lakes, and different water sources in North America and the Indian subcontinent have been surveyed. These studies show that water from the ocean depth has an average D-content of 156 1 ppm, with little variation, whereas the same for surface water is lower. D-content of tropical seawaters is around 160 1 ppm. Freshwater samples show large variations due to isotopic fractionation, which occur when water evaporates from land or sea and is condensed from air. Various factors such as local weather conditions, altitude, latitude, mean air temperature, drainage pattern, distance from the ocean, average precipitation, etc. are responsible for these variations. 

The solubility of elements in freshwater is limited and the solubility of calcium and magnesium carbonates are of particular importance in freshwaters. The solubility of carbonates is inversely proportional to the temperature of the water. In other words, as the water temperature increases, calcium and magnesium carbonates become less soluble. If the solubility decreases sufficiently, carbonates will precipitate and form a scale on the surfaces of the system. This scale can provide a protective barrier to prevent corrosion of the metallic elements in a system. Excessive scale deposits can interfere with water flow and heat transfer. The quality of the scale is dependent on the quantity of calcium that can precipitate as well as water flow and the chloride and sulfate content of the water. The tendency of water to precipitate a carbonate scale is estimated from corrosion indices such as the Langelier Saturation Index (LSI) and Caldwell-Lawrence calculations [6-8] which use calcium, alkalinity, total dissolved solids, temperature and pH properties of the water. Other indices, such as the Ryznar Index... 

As liquid water is heated above the melting point, hydrogen bonds continue to break. The molecules become even more closely packed, and the density of the liquid water continues to increase. Liquid water attains its maximum density at 3.98 °C. Above this temperature, the water behaves in a "normal" fashion Its density decreases as temperature increases. The unusual freezing-point behavior of water explains why a freshwater lake freezes from the top down. When the water temperature falls below 4 °C, the denser water sinks to the bottom of the lake and the colder surface water freezes. The ice over the top of the lake then tends to insulate the water below from further heat loss. This allows fish to survive the winter in a lake that has been frozen over. Without hydrogen bonding, all lakes would freeze from the bottom up and fish, small bottom-feeding animals, and aquatic plants would not survive the winter. The density relationship between liquid water and ice is compared in Figure 12-8 with the more common liquid-solid density relationship. 

Fluids on the Earth s surface that are in hydrostatic equilibrium may be stable or unstable depending on their thermal structure. In the case of freshwater (an incompressible fluid), density decreases with temperature above ca. 4°C. Warm water lying over cold water is said to be stable. If warm water underlies cold, it is buoyant it rises and is unstable. The buoyant force, F, on the parcel of fluid of unit volume and density p is ... 

These changes may be related to the two warm winters that occurred in 1998 and 1999, which could affect the balance between input of freshwater from the rivers and saline water from the Bosporus and the winter formation of the oxygen-rich CIL. These years are remarkable for the increase of the Sea surface temperature (Fig. 8), increase of temperature in the core of the CIL [82,85-87], and shoaling of the CIL in the density field [48]. All these events can be connected with the weather condition oscillations, as follows from North Atlantic oscillation (NAO) index behavior (Fig. 8). 

The 5 0 from the calcite tests of benthic foraminifera preserved in ocean sediments can be used to estimate upper-ocean density because both the 5 0 of calcite (S Ocaicite) and density increase as a result of increasing salinity or decreasing temperature (Lynch-Stieglitz et al., 1999a). The fractionation between calcite precipitated inorganically and the water in which it forms increases by 0.2%c for every 1 °C decrease in temperature (Kim and O Neil, 1997). The relationship between S Ocaidte and salinity is more complex. The S Ocaidte reflects the 5 0 of the water in which the foraminifera grew. The 5 0 of seawater (S Owater) primarily reflects patterns of evaporation and freshwater influx to the surface of the ocean. Because salinity also reflects these same processes, salinity and... 

Working together, salinity and temperature regulate water s density. Density of water is an important factor because it determines where water will be located in the water column, water below the surface. Since denser water sinks below less dense water, both very salty and extremely cold waters move to the lowest levels of water columns. Cold, salty water is the densest kind. Warm seawater that is mixed with some freshwater is not dense, so it rides on top of the water column. In many coastal areas, the influx of freshwater from streams and rivers reduces the density of the ocean water. 

The horizontal ice distribution simulated with such a low order ice model resembles the observed distributions of sea ice however, the storage of freshwater in the ice and the formation of a new water mass by freezing with brine release and by melting is neglected. To include these features, the three-level ice model of Winton (2000) is coupled with MOM-3.1 to provide an improved representation of sea ice for long-term simulations. The sea ice is vertically resolved by two ice layers and a snow cover, with different development of thickness and temperature. As shown in Fig. 19.3, this local thermodynamic description yields arealistic simulation of the interannual variation in the thickness and the spatial extent of the ice cover in the Baltic Sea. The transfer of wind momentum to the currents and to surface waves is exponentially damped out if the ice thickness exceeds a critical value, for example, 10 cm, assuming fast ice. 

Water s great versahlity stems, in part, from a tendency TO form aqueous SOLUHONS by DISSOLVING A LARGE VARIETY OF SOLIDS AND OTHER LIQUIDS THE FACT THAT IT EXISTS AT NORMAL AIR TEMPERATURE AS A LIQUID IS DUE TO THE UNIQUE PROPERTY OF ITS MOLECULES. Even though water covers 70 percent of Earth s surface, IT IS RARE TO FIND PURE WATER IN NATURE. SeAWATER AND FRESHWATER SOURCES ALIKE CONTAIN DISSOLVED MINERALS AND CONTAMINANTS SUCH AS FERHLIZERS AND INDUSTRIAL POLLUTANTS. AS FOR THE WATER THAT COMES FROM THE TAP, IT GENERALLY CONTAINS FLUORIDES (ADDED TO REDUCE TOOTH DECAY) IN ADDIHON TO MINERALS (PRINCIPALLY CHLORIDES, SULFATES, BICARBONATES OF SODIUM, POTASSIUM, CALCIUM, AND MAGNESIUM), AND POSSIBLY ADDIHONAL CHLORINE (TO KILL BACTERIA) AND LEAD (IF THE PIPES CARRYING IT ARE MORE THAN 80 YEARS OLD). 

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