Estuary

Water flow in estuaries is more complicated than in rivers and in lakes it is influenced by the inflow of freshwater from rivers and streams, by the tides of the ocean, and by the large salinity—and hence density—difference between fresh- and ocean water. The density difference tends to create a strong stratification, while the back-and-forth movement of water driven by the tides 

Mean Salinity Profile Mean Velocity Profile 

FIGURE 2-9 (a) An idealized estuary in cross section. In this well-stratified estuary, a distinct 

Simple transport models have significant limitations in a complex estuarine setting commonly, sophisticated numerical models are employed to predict transport in estuaries. In long, narrow estuaries, however, a simple onedimensional model, such as is used in rivers, that incorporates a longitudinal dispersion coefficient and a time-averaged seaward water velocity can be useful. The results of such a model must be averaged over the tidal cycle concentrations at each point in the estuary may be expected to vary significantly with the state of the tide. See Fischer et al. (1979) for a more complete discussion of transport in estuaries. 

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. 

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Monna and co-workers studied the use of radioactive isotopes as a means of dating sediments collected from the bottom of lakes and estuaries. To verify this method they analyzed a 208po standard known to have an activity of 77.5 decays/min, obtaining the following results... 

The environmental sampling of waters and wastewaters provides a good illustration of many of the methods used to sample solutions. The chemical composition of surface waters, such as streams, rivers, lakes, estuaries, and oceans, is influenced by flow rate and depth. Rapidly flowing shallow streams and rivers, and shallow (<5 m) lakes are usually well mixed and show little stratification with... 

Sediments from the bottom of streams, rivers, lakes, estuaries, and oceans are collected with a bottom grab sampler or with a corer. Grab samplers are equipped with a pair of jaws that close when they contact the sediment, scooping up sediment in the process (Figure 7.5). Their principal advantages are ease of use and the ability to collect a large sample. 

Sources of water for aquaculture include municipal suppHes, wells, springs, streams, lakes, reservoirs, estuaries, and the ocean. The water may be used directly from the source or it may be treated in some fashion prior to use (see Water). 

Fig. 5. Typical thermal stratification of a lake, reservoir, or poorly mixed estuary in summer which, because of density differences, estabUshes discrete 2ones...

With the possible exception of systems using sea water, estuarial waters, and/or industrially contaminated waters for cooling, condi-... 

W. P. Davis and S.A. Bortone, Advances in Modern Environmental Toxicology Volume XXL Chemically-Induced Alterations in Sexual and Eunctional Development The Wildlife/Human Connection, ed. T. Colborn and C. Clement, Princeton Scientific, New Jersey, 1992, p. 113. D.L. MacLatchy, Z. Yao, L. Tremblay and G.J. Van Der Kraak, in Proceedings of the 5th International Symposinm on Reprodnctive Physiology of Eish, University of Texas, Austin, 1997, p. 189. P. E. Gibbs and G. W. Bryan, in Biomonitoring of Coastal Waters and Estuaries, ed. K. J. M. Kramer, CRC Press, Boca Raton, FL, 1994, p. 205. 

This removal may also include diffusion of soluble U(VI) from seawater into the sediment via pore water. Uranium-organic matter complexes are also prevalent in the marine environment. Organically bound uranium was found to make up to 20% of the dissolved U concentration in the open ocean." ° Uranium may also be enriched in estuarine colloids and in suspended organic matter within the surface ocean. " Scott" and Maeda and Windom" have suggested the possibility that humic acids can efficiently scavenge uranium in low salinity regions of some estuaries. Finally, sedimentary organic matter can also efficiently complex or adsorb uranium and other radionuclides. 

In 1974, the Harmonized Monitoring Programme was set up by the Department of the Environment (DoE). The objective was to provide a network of sites at the lower end of catchments, where water quality data could be collected and analysed in a nationally consistent manner, allowing the loads of materials carried through river catchments into estuaries to be estimated and long-term trends in river quality to be assessed. The complete list of substances to be monitored is diverse and specifies about 115 substances. The pesticides aldrin, dieldrin, y-HCH, heptachlor, p,p -DDT and p,p -DDE are included. Figures 1 and 2 show the downward trend of y-HCH and dieldrin over the past 20 years at the Harmonized Monitoring Sites. This confirms that reductions in environmental concentrations have been achieved, particularly over the past 10 years. 

Similarly, contaminant concentrations in rivers or streams can be roughly assessed based on rate of contaminant introduction and dilution volumes. Estuary or impoundment concentration regimes are highly dependent on the transport mechanisms enumerated. Contaminants may be localized and remain concentrated or may disperse rapidly and become diluted to insignificant levels. The conservative approach is to conduct a more in-depth assessment and use model results or survey data as a basis for determining contaminant concentration levels. 

Equalizing basin A holding basin in which variations in flow and composition of liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir. Estuaries Bodies of water which are located at the lower end of a river and are subject to tidal fluctuations. 

Ships in passage travel fairly close to the jetties and sea walls of the river bank within the area. All vessels within the estuary are navigated under requirements of the Thames Navigation Sen,dce of the Port of London Authority. 

As the result of a mix-up at a distribution center, two tank track drivers received each other s papers. One of the trucks carried a load of sodium chlorite solution, and the other carried epichlorohydrin. The chlorite truck went to the customer who was expecting epichlorohydrin and was off-loaded into a tank that already contained some epichlorohydrin. The result was an explosion and a serious fire fumes and smoke led to the closure of the bridges over the Severn Estuary. UK [12, 13]. 

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