Bottom sediments inputs

POCs proportions and content of POCs in river waters compared with maximum permissible concentration (MPC, for DDT, HCH and PCB, are equal to 100,20 and 1 ppb correspondingly for water and 100,100 and 100 for bottom sediments) behavior of toxic compounds in the water body factors promoting an increase of the ecological risk of polluted riverine input into the Caspian Sea (Figure 4). 

Bottom sediments in water bodies accumulate various toxic compounds due to their high adsorption rate on the particle surface (this varies with particle type) and low temperature of the bottom layer, which reduces the transformation rates. The largest amount of toxic compounds is accumulated in the subsurface silt or clay layers with anaerobic conditions (Rhee et al., 1989). At present a hundred thousands tons of POCs have been stored in the bottom sediments, and their continued input into the water column adds to present contamination (Afanasiev et al., 1989). 

Thus, at present, the input of unused DDT and HCH insecticides in water and bottom sediments of the rivers and reservoirs of the Caspian Sea basin is mainly connected with loss or leaching from old RPA or young LPA. As regards PCBs, their input is mainly related to industrial sources. The high toxicity of POCs for organisms and their persistence in the water and sediments are the principal forms of ecological risk for rivers and the Caspian Sea. The behavior of POCs in the northern part of... 

Permanent accumulation of Hg in the bottom sediments was roughly balanced by atmospheric inputs on an annual basis. 

Particulate material (e.g., sand, silt, clay) which has been transported and deposited in the bottom of a body of water. Sediment input to a body of water comes from natural sources, such as erosion of soils and weathering of rock, or as the result of anthropogenic activities, such as forest or agricultural practices, or construction activities. The term can also describe a material that has been experimentally prepared (formulated) using selected particulate material (e.g., sand of particular grain size, bentonite clay, etc.). Volume 1(2), Volume 2(5,9). 

Some amounts of sand riverine sediments are transported in channels in the form of sand ripples, waves and dunes formed on the river bed under the influence of the near-bottom currents. This sediment load (called bedload) usually comprises about 10% of the suspended sediment load. Taking into account this fact, we find that the total river sediment input to the Black Sea may range up to 84 x 106 tyear-1. 

FIGURE 14.14 Sedimentary fluxes of total organic carbon (TOC), total nitrogen (TN), and total phosphoms (TP) subdivided into vertical flux (1), near bottom lateral input (2), release flux back to the water (3), and sediment net accumulation (4) in surface sediments of the Eastern Gotland Basin below 150-m water depth. Arrow thickness indicates the relative proportion of lateral and vertical input and release. The gray hue represents the sediment surface. 

Bordovsky (1974) is right in his belief that HA of marine deposits is of autochthonous and allochthonous origin, the latter playing a minor role. Based on chemical investigations and isotope determinations of C in HA isolated from ocean sediments, Nissenbaum smd Kaplan (1972) do not seree with this point of view. The allochthonous HA in the bottom sediments of the ocean is evidently at the limits of detection of the analyticsil methods employed. According to Table IX the total annual input of water humus to the ocean constitutes 1.5 X 10 g C, provided the distribution is proportional, this amounts to 1 pg C T . 

Level II Model The added refinement involves accounting for losses from compartments either by advection or reaction. A steady state is achieved where input is balanced by the loss from the system, but the compartments remain at equilibrium as indicated by the fluid height in the tank analogy (Fig. 10.9). Quantities defining the loss of 1,2,3-trichlorobenzene from the system by advection and reaction are compiled in Table 10.8. Photochemical reactions would be the most likely processes involved in air and water, while microbial degradation would be active in soil and bottom sediments, and the use of first-order rate constants (h ) is an appropriate approximation. 

Air and water transport of technical chlordane has resulted in the detection of chlordane and its metabolites in nonbiological samples worldwide. Chlordane enters the atmosphere mainly through aerial applications of dust and spray formulations, soil erosion by wind, and volatilization from soil and water. In aquatic systems, chlordane enters by way of surface runoff and rainfall chlordane is rapidly adsorbed onto bottom sediments, where it persists. Atmospheric transport of chlordanes is considered the major route of global dissemination. Levels of chlordane compounds in the marine atmosphere of the southern hemisphere are nearly the same as those of DDT and its metabolites this strongly suggests that chlordane compounds are globally distributed and dispersed. The yearly input of m-chlordane to the Arctic Ocean from atmospheric sources is... 

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