Sediments redeposition

Sediments redeposited during solifluctional and other mass movements of the glacials of the Pleistocene are also included here. 

Where the waves and currents weaken, resuspended sediment settles back down to the seafloor. Given the small particle sizes of the suspended material (mostly 3 to 10 pm), redeposition can take many years. The resulting redistribution of sediments creates patches of clay, mud, and exposed rock on the continental margins. In other words, resuspension from waves and currents can cause some sediments to become reUct deposits. Hard bottoms can serve as good habitats for some members of the benthos as they promote the formation of coral reefs. For paleoceanographers, relict deposits are problematic because they represent gaps, or imconformities, in the sedimentary record. 

Turbidity and contour currents resuspend and transport the sediments that lie on the continental margin. These sediments are redeposited when the currents weaken. 

The capital cost for construction and initial testing of a single 25,000 ton a year transportable AER is approximately 4 million, not including permits and trial burns. With six units, it would require approximately 3.5 years to treat 382,000 m of sediment. Including dredging and transport for treatment and redeposition or treated sediments the overall cost estimate would equal 829 to 942/m2 (D13468J, p. 53). 

The estimated cost for the Soilex process is 856 to 913/m of treated soil. This estimate includes dredging, transportation, treatment, and redeposition of the treated sediments (D13464F, p. 67). 

Assuming most PAH are stable in the atmosphere, which we feel is an excellent assumption, we ask what happens to these compounds after they are released from combustion systems throughout the world. We suggest that PAH are transported to a-quatic sediments either by direct airborne transport or by sediment resuspension and redeposition. 

In the biosphere, vanadium can be considered to be of two forms, one of which is highly mobile, whereas the other is a virtually immobile form. These are closely connected to the oxidation state of vanadium, where the mobile chemically reactive form conforms more or less, but certainly not exclusively, to the V(V) oxidation state. This is the state that vanadium will predominantly have in gas effluents in ash from oil, coal, and gas burners in some minerals and in surface water. Vana-dium(IV) complexes of the types found in minerals will often be relatively immobile but, if subjected to an oxidative environment, can enter the mobile phase in the V(V) oxidation state. Sequestered forms of vanadium can be transported by mechanical processes such as by movements of suspended materials in creeks and rivers, where translocation from terrestrial to lake or marine environments accounts for a high percentage of the movement of vanadium. This procedure does not release the vanadium into the environment in the sense that release from the substrate does rather, the vanadium is simply redeposited as the sediments settle. However, because of the high surface area of the suspended materials, vanadium can efficiently be removed from the suspended material by chemical reactions and enter into the environment as active species by this process. 

Figure 7.19b Susquehanna River discharge (a), 7Be atmospheric deposition (b), and 7Be inventories in Chesapeake Bay (USA) (c-h), showing lower inventories at the SUSQ station relative to the higher inventories at the BALT and CALV stations due to inputs of 7Be-rich sediments from the head of the Bay followed by redeposition farther down in the estuary. (Modified from Dibb and Rice, 1989.)...

A third research theme suggested by our geochemical studies of Pre-dynastic ceramic technology at Hierakonpolis deals with the differences in methods of production between Plum Red and Straw Tempered wares. Initially, we suggested that the somewhat increased Ca content in the Plum Red Ware may have been due to the deliberate addition of Ca salts (27). The present studies of the wadi sediments and Unit C suggest, however, that the older Nile sediments contain an acid-soluble Ca phase deposited, much like the Fe, on the surface of particles. Finer grained particles with more surface area appear to contain most of this soluble Ca. This Ca probably originates from the Ca salt deposits in the older shale sediments that are redeposited from solution onto the Nile sediments. 

The rate constants calculated by EF profiles (Equation (4.6)) are necessarily crude as several assumptions must hold the initial enantiomer composition is known, only a single stereoselective reaction is active, and the amount of time over which transformation takes place is known. These assumptions may not necessarily hold. For example, for reductive dechlorination of PCBs in sediments, it is possible for degradation to take place upstream followed by resuspension and redeposition elsewhere [156, 194]. The calculated k is an aggregate of all reactions, enantioselective or otherwise, involving the chemical in question. This includes degradation and formation reactions, so more than one reaction will confound results. Biotransformation may not follow first-order kinetics (e.g. no lag phase is modeled). The time period may be difficult to estimate for example, in the Lake Superior chiral PCB study, the organism s lifespan was used [198]. Likewise, in the Lake Hartwell sediment core PCB dechlorination study, it is likely that microbial activity stopped before the time periods selected [156]. However, it should be noted that currently all methods to estimate biotransformation rate constants in field studies are equally crude [156]. 

The change in character of sedimentation at the beginning of the Late Precambrian is explained by the fact that by this time a thick mantle of Middle Precambrian (Lower Proterozoic) sediments had arisen on the ancient continents. Subsequent denudation, erosion, and redeposition of these rocks, granitized to a considerable extent, contributed to further profound differentiation of matter. An increase in the role of the life activity of various organisms in sedimentation also was an important fact. 

Before the beginning of deposition of iron the original sediments were redeposited siliceous-aluminous products of terrestrial or submarine leaching of basalts. 

Wallace et al. (1995) and Wallace (2001) have explored this issue in detail, and ScaiUet et al. (1998, 2003) and ScaiUet and Pichavant (2003) have advanced petrological modeUng approaches to circumvent the problem by estimating the volatile contents contained in the vapor phase prior to emption. Another problem with petrological estimates of volatile yields is that they scale linearly with the emption magnitude, which is often only poorly constrained from the rock record. This is especially tme in cases where tephra dispersal is very widespread, perhaps largely at sea, and where substantial burial, erosion or redeposition limit efforts to identify original thicknesses of sediment in the field. 

Particulate RI compounds sink to the sediments, where I is released during diagenesis. Some decomposition occurs in the deep waters, releasing low levels of T to the deep waters where it is not likely to be chemically reoxidized. Some of the volatile iodine compounds or sea salt spray containing iodide are reoxidized in the atmosphere, perhaps to iodate, which is redeposited to the ocean as wet or dry deposition. 

All stations in less than about 20 m of water are subject to constant resuspension of surface sediment creating highly turbid conditions. During major storms the upper few centimeters at these stations may be eroded and redeposited (Aller and Cochran, 1976 McCall, 1978), but normally only the top 1 mm or so is subject to resuspension (Bokuniewicz,... 

In the ocean, the material advected by the rivers participates in the formation of new sediments whereby the geochemical cycle is closed. The suspended load is redeposited in the continental shelf regions. The dissolved elements are temporarily stored in the ocean reservoir before they, too, are incorporated into sedimentary deposits. In the long run, the river influx must be balanced by an appropriate sedimentary output for each element considered. A certain degree of accumulation is nevertheless evident from the higher concentrations of the principal ions in seawater as compared to those in river water (Table 11-7, columns 6 and 7). Residence times in the ocean can be computed by means of Eq. (4-11) from the ratio of the reservoir s mass content to the observed river influx. The residence times... 

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