Salinity surface water

The density of seawater thus depends both on its temperature and salinity. Highly saline waters at about 4°C are the most dense and will tend to sink, whereas warm, less saline water is less dense, and will tend to rise. This behavior has important implications for vertical motions in the sea. Descent of surface waters to the deep ocean is possible only where saline waters are cooled. This actually occurs in only a few locations, most notably in the North Atlantic off Greenland, and in the Weddell Sea, part of the Antarctic Ocean south of the Atlantic. North Atlantic deep water has a temperature of 2.5°C and a salinity of 35 g salt per kg of seawater. Deep water forming in the Weddell Sea has a temperature of — 1.0°C and a salinity of 34.6 g salt per kg seawater. In both of these locations, saline surface waters are cooled and sink, a process known as downwelling. The surface waters are made saline by evaporation nearer the equator in the case of the North Atlantic, and by the formation of sea ice in the case of the Weddell Sea. Shallower downwelling, to intermediate depths in the oceans, also occurs in areas of high evaporation. 

Hydrosphere Large quantities of water are used for irrigation. Some of the water is lost by transpiration Irom plants, and some by infiltration to groundwater. Water returned to the hydrosphere irom irrigation may have an excessively high salinity. Surface water and groundwater may become contaminated by solids, fertilizers, and herbicides Irom crop production. 

Water in Industry. Freshwater for industry can often be replaced by saline or brackish water, usually after sedimentation, filtration, and chlorination (electrical or chemical), or other treatments (22). Such treatment is not necessary for the largest user of water, the electric power industry, which in the United States passed through its heat exchangers in 1990 about 40% of the total supply of surface water, a quantity similar to that used for agriculture, and it was 48% of the combined fresh and saline water withdrawals (10). Single stations of 1000 MW may heat as much as 12 Mm /d by as much as 10—15°C. 

Variability of Seawater Vertical sections through seawater showing the distribution of temperature, salinity, and oxygen for the Pacific Ocean and Western Atlantic Ocean are shown in Figures 21.3 and 21.4. The global variability of natural seawater and its effects on corrosion have been reviewed in particular with respect to seasonal variation of temperature, salinity, oxygen and pH in the Pacific surface water. Data is also given on... 

Ocean prevents eutrophication. Much more water flows into the Mediterranean Sea than is required to replace evaporation from it. The excess, high salinity water exits Gibraltar below the water flowing in af fhe surface. Nufrients that enter the Mediterranean Sea from pollution sources are utilized by marine phytoplankton that sinks and exits with the outflow. Another example is that estuaries often have lower salinity or even freshwater at the surface with a denser saline layer at the bottom. An estuarine circulation occurs with nutrients being trapped in the saline bottom water. 

When TBTO is released into ambient water, a considerable proportion becomes adsorbed to sediments, as might be expected from its lipophilicity. Studies have shown that between 10 and 95% of TBTO added to surface waters becomes bound to sediment. In the water column it exists in several different forms, principally the hydroxide, the chloride, and the carbonate (Figure 8.5). Once TBT has been adsorbed, loss is almost entirely due to slow degradation, leading to desorption of diphenyl-tin (DPT). The distribution and state of speciation of TBT can vary considerably between aquatic systems, depending on pH, temperature, salinity, and other factors. 

Figure 3. Time series of nitrate (Slagle and Heimerdinger 1991) and dissolved, particulate, and total in surface water at 47°N, 20°W (Atlantic Ocean) in April-May 1989. activity calculated as 0.0686 salinity (Chen et al. 1986). The production of biogenic particles during the bloom enhances the scavenging of Th, resulting in growing disequilibrium with time due to sinking of particles.

Surface water information, including drainage patterns (overland flow, topography, channel flow pattern, tributary relationships, soil erosion, and sediment transport and deposition), surface water bodies (flow, stream widths and depths, channel elevations, flooding tendencies, and physical dimensions of surface water impoundments structures surface water/ groundwater relationships), and surface water quality (pH, temperature, total suspended solid, salinity, and specific contaminant concentrations)... 

For comparison, the periods of enhanced blue crab yield, of maxima of air temperatures at Philadelphia (which is close to the Chesapeake Bay), of minima of rainfall at Philadelphia, and of enhanced tidal forces (leading to high tides) are listed in Table 5. The explanation we offer for the agreement among the periods so listed is that high tides wash nutrient into the surface waters of the Bay, and higher temperatures warm the surface waters, and minimum rainfall allows the surface waters to become more saline, all of which factors are salubrious for crab growth. 

In general, silver concentrations in surface waters of the United States decreased between 1970-74 and 1975-79, although concentrations increased in the north Atlantic, Southeast, and lower Mississippi basins (USPHS 1990). About 30 to 70% of the silver in surface waters may be ascribed to suspended particles (Smith and Carson 1977), depending on water hardness or salinity. For example, sediments added to solutions containing 2 pg Ag/L had 74.9 mg Ag/kg DW sediment after 24 h in freshwater, 14.2 mg/kg DW at 1.5% salinity and 6.9 mg/kg DW at 2.3% salinity (Sanders and Abbe 1987). Riverine transport of silver to the ocean is considerable suspended materials in the Susquehanna River, Pennsylvania — that contained as much as 25 mg silver/kg — resulted in an estimated transport of 4.5 metric tons of silver to the ocean each year (USEPA 1980). The most recent measurements of silver in rivers, lakes, and estuaries using clean techniques show levels of about 0.01 pg/L for pristine, nonpolluted areas and 0.01 to 0.1 pg/L in urban and industrialized areas (Ratte 1999). 

Analysis for such isotopes as carbon and deuterium has been conventionally used to assess the relative age of groundwater, and in evaluating its origin (i.e., meteoric, juvenile, formation, etc.), chemistry, and total salinity. Isotope composition of ground-water and surface water has also been used to correlate between areas of precipitation and groundwater, thus providing an indication of source area(s) of recharge. 

It is difficult to compare recoveries obtained by different laboratories because their extraction conditions (pH, phase ratio, number and time-length of extractions, salinity) are generally different. Sample volumes can be very high, up to 200 1 [433], and 50 1 of surface water [434] or 201 of sea water allow the extraction of 5 ng/1 of alkanes. When using a specific detection method, the sample volume can be lower 2 ng/1 of PAH was determined from 11 of river water using liquid chromatography and fluorescence detection [435]. Chlorophenols below the 10 ng/1 level were determined from 100 ml of sea water with electron capture detection (ECD) GC [436]. 

Concentrate can be harmful to the environment due to either its higher than normal salinity, or due to pollutants that otherwise would not be present in the receiving body of water. These include chlorine and other biocides, heavy metals, antisealants, coagulants and cleaning chemicals. Of particular concern is the effect of pollutants on delicate ecosystems and endangered or threatened species. However, with appropriate measures in place, the discharge of concentrate to surface water can remain a viable method for seawater desalination plants. 

This is why the salinity of seawater is nearly the same throughout the open ocean, varying by only a few parts per thousand. (As per Figure 3.3, 75% of seawater has a salinity between 34 and 35 %o.) The small degree of spatial variability is a consequence of geographic variations in the balance of evaporation versus precipitation in the surface waters. Recall that these surface waters are the source waters for intermediate and deep water masses. Since shifts in the relative rates of evaporation versus precipitation involve only addition or removal of water, the major ion ratios are unaltered. This is why the major ion ratios do not exhibit little if any spatial differences within the open ocean. 

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