Watersheds Surface waters

Surface Water Naturally available fresh water on the earth s surface in rivers, lakes or wetlands is called surface water. Natural replenishment of surface water takes place through precipitation. Surface water is depleted through natural processes like evaporation, discharge to seas and oceans and sub surface seepage. Human activities can have severe detrimental effects on the quality and availability of surface water. The upper limit of human consumption is restticted by the rate of precipitation within a watershed. Pulling in water from other watersheds through canals or pipelines can increase natural surface water in a particular watershed. Surface water is more prone to pollution from various human actions and needs extensive treatments to make it suitable for human consumption. 

Consider a lake with a smaU watershed in a forest ecosystem. The forest and vegetation can be considered as an acid concentrator. SO2, NO2, and acid aerosol are deposited on vegetation surfaces during dry periods and rainfalls they are washed to the soil floor by low-pH rainwater. Much of the acidity is neutralized by dissolving and mobilizing minerals in the soil. Aluminum, calcium, magnesium, sodium, and potassium are leached from the soil into surface waters. The ability of soils to tolerate acidic deposition is very dependent on the alkalinity of the soil. The soil structure in the... 

Many hydrologic reservoirs can be further subdivided into smaller reservoirs, each with a characteristic turnover time. For example, water resides in the Pacific Ocean longer than in the Atlantic, and the oceans surface waters cycle much more quickly than the deep ocean. Similarly, groundwater near the surface is much more active than deep reservoirs, which may cycle over thousands or millions of years, and water frozen in the soil as permafrost. Typical range in turnover times for hydrospheric reservoirs on a hillslope scale (10-10 m) are shown in Table 6-4 (estimates from Falkenmark and Chapman, 1989). Depths are estimated as typical volume averaged over the watershed area. 

The role of radionuclides as tracer of the chemical transport in river is also reinforced by the fact that each of the U-Th-Ra elements has several isotopes of very different half-lives belonging to the U-Th radioactive series. Thus, these series permit comparison of the behavior of isotopes of the same element which are supposed to have the same chemical properties, but very different lifetimes. These comparisons should be very helpful in constraining time scales of transport in rivers. This was illustrated by Porcelli et al. (2001) who compared ( " Th/ U) and ( °Th/ U) ratios in Kalix river waters and estimated a transit time for Th of 15 10 days in this watershed. The development of such studies in the future should lead to an important progress in understanding and quantifying of transport parameters in surface waters. This information could be crucial for a correct use of U-series radioactive disequilibria measured in river waters to establish weathering budgets at the scale of a watershed. 

One weakness of some multimedia models that must be considered by the user is inconsistency of time scales. For example, if we employ monthly averaged air concentrations to get rainout values on fifteen-minute interval inputs to a watershed model, large errors can obviously occur. The air-land-water-simulation (ALWAS) developed by Tucker and co-workers (12) overcomes this limitation by allowing for sequential air quality outputs to provide deposition data to drive a soil model. This in turn is coupled to a surface water model. 

Atmospheric deposition is an important source of mercury for surface waters and terrestrial environments that can be categorized into two different types, wet and dry depositions. Wet deposition during rainfall is the primary mechanism by which mercury is transported from the atmosphere to surface waters and land. Whereas the predominant form of Hg in the atmosphere is Hg° (>95%), is oxidized in the upper atmosphere to water-soluble ionic mercury, which is returned to the earth s surface in rainwater. In addition to wet deposition of Hg in precipitation, there can also be dry deposition of Hg°, particulate (HgP), and reactive gaseous mercury (RGM) to watersheds [9-11]. In fact, about 90% of the total Hg input to the aquatic environment is recycled to the atmosphere and less than 10% reaches the sediments [12]. By current consensus, it is generally accepted that sulfate-reducing bacteria (SRB)... 

Hall, L.W., Jr., M.C. Scott, and W.D. Killen. 1998. Ecological risk assessment of copper and cadmium in surface waters of Chesapeake Bay watershed. Environ. Toxicol. Chem. 17 1172-1189. 

Surface water samples were also collected at a number of sites throughout the Ruby Creek watershed although only data collected from active stream flow were utilized here. The surface water data was also categorized into background areas (n=13) and sites downstream from mineralization area (n=21). 

Table 2. Significant differences between median (mg/L) background (BACK) and mineralized(MINER) area in ground and surface water in the Ruby Creek Watershed...

Very little recent information on concentrations of endrin in water could be found in the available literature. Unlike DDT, chlordane, aldrin/dieldrin, and a variety of other chlorinated pesticides, endrin was never used extensively in urban areas. This is reflected in the results from EPA s Nationwide Urban Runoff Program, which showed no detections in 86 high-flow water samples from 51 urbanized watersheds from 19 cities (Cole et al. 1984). Analysis of EPA STORET monitoring information from ambient surface water showed a significant percentage of detections for endrin (32% of 8,789 samples), but most were near the detection limits, with a national median concentration of 0.001 ppb (Staples et al. 1985). A similar analysis of STORET data for endrin aldehyde showed that this compound was not found in 770 samples of ambient surface water. More recently, endrin was not detected (detection limit 49 ng/L [0.045 ppb]) in surface water from the Yakima River Basin, Washington (Foster et al. 1993). However, in... 

The COLEX units operated between 1955 and 1963. Approximately 24 million pounds of mercury were employed and, unfortunately, a good deal was lost through waste, accidental spills, and evaporation. In fact, about 2 million pounds have not been accounted for. The process discharged approximately a quarter million pounds into the surface waters in the vicinity of the plant, and much of this remains in the bottom sediments of the watershed. 

Hites 1978, 1979). The annual mean concentration of phenol in water from the lower Mississippi River was 1.5 ppb (EPA 1980). River water in an unspecified location in the United States was reported to contain 10-100 ppb of phenol (Jungclaus et al. 1978). Phenol was detected, but not quantified, in a Niagara River watershed (Elder et al. 1981) and in 2 of 110 raw water samples analyzed during the National Organic Monitoring Survey (EPA 1980). In the STORET database, 7% of 2,181 data points for U.S. surface waters were positive for the presence of phenol the mean and range of the reported concentrations were 533 ppb and 0.002-46,700 ppb, respectively (EPA 1988c). 

Surface Water. Endosulfan sulfate was identified as a metabolite in a survey of 11 agricultural watersheds located in southern Ontario, Canada (Frank et al, 1982). When endosulfan (a- and p-isomers, 10 pg/L) was added to Little Miami River water, sealed, and exposed to sunlight and UV... 

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