River sediment discharge

The accumulation of sediments in estuaries appears to be so effective that Meade (1981) has estimated that, "Probably less than 5 percent of all river sediment discharged into the tidal waters of the Atlantic seaboard is deposited on the floor of the continental shelf or the deep sea". These sediments contain an often dramatic imprint of human activity and impact on the estuary and its watershed. But it is an imprint which results not only from the input of materials, but also from the interaction of a great variety of physical, chemical and biological processes in the estuary. We are only beginning to learn to read that record, but the early results suggest that we may learn more about what flows between rivers and the sea from the humble muds on the estuary floor than we can from the water above. 

River Sediment discharge (106 ty 1) Sediment discharge rank Water discharge (109 m3 y 1) Water discharge rank Drainage basin area (106 km2)... 

A summary of physical and biochemical parameters for the Amazon shelf are presented in Table 17.1. These data were used to develop the mass balance calculations described in the remainder of the paper. The rate of Amazon River sediment discharge that is cited in most studies (Meade et al. 1985) characterizes the flux at Obidos, which is hundreds of kilometers from the river mouth. The sediment fluxes that have been documented for the Amazon coastal area are the fine-grained sediment accumulation rate on the shelf (6.3 x 10 g yr, Kuehl et al. 1986, 1996) and the advection rate of particulate material northward out of the study area, primarily in nearshore environments (-1.2 X 10 g yr, Allison et al. 1995). Because some sediment may be deposited between Obidos and the river mouth, we have chosen to use the sum of the shelf... 

Milliman, J. D. and Syvitski, J. P. M. (1992). Geomorphic/tectonic control of sediment discharge to the ocean The importance of small mountainous rivers. /. Geol. 100, 525-544. 

Liquete C, Canals M, Ludwig W, Amau P (2009) Sediment discharge of the rivers of Catalonia, NE Spain, and the influence of human impacts. J Hydrol 366 76-88... 

Ying, M., Li, J.F., Wan, X.N., Shen, H.T. 2005. Study on Time Series of Sediment Discharge at Datong Station in the Yangtze River. Resources and Environment in the Yangtze Basin, 14(1), 83-87(in Chinese). 

The major part of the biosphere is aerobic and consequently priority has been given to the study and assessment of biodegradability under aerobic conditions. Nevertheless, there are environmental compartments that can be permanently (e.g. anaerobic digesters) or temporarily anaerobic (e.g. river sediments and soils) and surfactants do reach these. The majority of surfactants entering the environment is exposed to and degraded under aerobic conditions. This is the predominant mechanism of removal even in cases of absence of wastewater treatment practices (direct discharge) and it is estimated that less than 20% of the total surfactant mass will potentially reach anaerobic environmental compartments [1]. Only in a few cases, however, will the presence of surfactants in these compartments be permanent. The presence of surfactants in anaerobic zones is not exclusively due to the lack of anaerobic degradation. Physico-chemical factors such as adsorption or precipitation play an important role as well as the poor bioavailability of surfactant derivatives (chemical speciation) in these situations. 

Although adequate information is available from rivers of the temperate regions, they are very scarce for those of tropical rivers. Data reviewed by Milliman and Meade (1983) show that about 70 % of the total sediment discharge to the oceans occur via the Southeast Asian rivers (Fig. lt). Inclusion of sediment data and the organic matter associated with these sediments might change drastically the net POC transport from land to sea. 

Data collected over the first two years of our study on DOC and POC were used to calculate annual fluxes of carbon from land to sea. The data are presented not for the individual rivers, but for rivers of a particular continent (Fig. 5). The measurement made in the major rivers of a continent were extrapolated to include the total water and sediment discharge from that particular continent. In terms of quantity maximum POC is being transported by the rivers of Asia, followed by those draining North America, Oceania, Africa and Europe, in that order. South American rivers carry maximum amounts of DOC, followed by the rivers of Asia, North America, the Arctic, Africa, Europe and Oceania. 

Livingstone, 1963 Burton and Liss, 1976 Meybeck, 1979 Berner and Berner, 1996). When examining the relationship between drainage basin area and total sediment discharge in major rivers of the world it becomes clear that factors other than basin area are important (table 4.2). In addition to basin area other factors typically include the following relief... 

Table 4.2 Sediment discharge and rank, water discharge and rank, and drainage basin area of the dominant rivers in the world.

By contrast, the sediment load of the Danube River has decreased because of reservoir construction, which was started in the Danube basin in the middle of the 20th century (Table 12). These data show marked human-induced decrease in the suspended sediment discharge and concentration with time. Reduction of the suspended sediment load of the Danube River was especially significant after 1971 and 1984, when the Iron-Gate-1 and Iron Gate-II reservoirs were put into operation (Fig. 5). 

Fig. 5 Long-term changes in the annual suspended sediment discharges of the Danube River at the delta head over the period 1840-2002 (six year moving mean was used)...

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