Suspended sediments

Disinfection - water completely free of suspended sediment, is treated with a powerful oxidizing agent usually chlorine, chlorine and ammonia (chloramine), or ozone. A residual disinfectant is left in the water to prevent reinfection. Chlorine can form harmful byproducts and has suspected links to stomach cancer and miscarriages. 

The most recent comprehensive assessment of the quality of rivers in the USA is that of Smith et al. 12), This followed an earlier assessment by Wolman et al. in 1971 (iS). The former 1987 assessment was based on 24 water quality measures from 161-383 stations around the country covering the period 1974-1981. Trends observed included major increases in nitrate, phosphorous, sodium, suspended sediment, fecal bacteria, dissolved oxygen deficit, arsenic and selenium. Major decreases were observed with nitrate, suspended sediment, fecal bacteria, dissolved oxygen deficit and lead. 

Rivers transport suspended sediments derived from the disintegration of basin surface layers. With reduced velocity, sediment is deposited in the river channel. The finest material is carried to the sea. It has been estimated that the average mechanical denudation rate for continents is 0.056 mm year (35). This is based on a total suspended load of 13.5 x 10 metric tons year (S). Presently, about two-thirds of the world s total suspended sediment load derives from Southern Asia and large Pacific Islands. Berner has estimated the increase in sediment loss in the U.S. and world since prehuman times to be approximately 200% (35). Current estimated erosion rate from the major land forms is provided in Table I. The relatively recent construction of large sediment trapping dams that normally caused sediment to be deposited in river valleys or transported to the ocean has drastically reduced sediment yields in great rivers. 

Figure 4. Discharge of suspended sediment from world rivers in 10 tons ear. Sediment yield in tons/km ear for major drainage basins is shown by pattern (see key).

Figure 8-8 Annual suspended sediment discharge. Relative discharge is indicated by the width of the arrows. (From Milliman and Meade, 1983, reproduced with permission from University of Chicago Press.)...

The travel time for suspended load is controlled by the flow velocity and the distance to the basin outlet. Flow velocities do not change much downstream in a typical river system (Leopold, 1953) and typically range from 0.1 to several m/s. Hence, suspended load should be able to travel at least 10 to 100 km per day and the travel time for suspended sediment to traverse even the longest rivers in the world should be less than a season. Although some of the suspended load will be deposited in floodplains, the component of the suspended load that does not get sequestered in terrestrial depositional environments is delivered almost as fast as the water that it flows in. Bedload travels much more slowly. In mountain drainage basins, the velocity of individual bedload clasts is on the... 

Tarras-Wahlberg NH, Lane SN (2003) Suspended sediment yield and metal contamination in a river catchment affected by El Nino events and gold mining activities the Puyango river basin, southern Ecuador. Hydrol Process 17 3101... 

Water quality issues for the lower Sacramento and San Joaquin rivers and for the Delta include salinity, dissolved organic carbon (DOC), suspended sediment. 

Hall IR, Schmidt S, McCave IN, Reyss J-L (2000) Suspended sediment distribution and Th-234/U-238 disequilibrium along the Northern Iberian Margin implication for particulate organic carbon export. Deep-Sea Res 147 557-582... 

DeMaster DJ, Kuehl SA, Nittrouer CA (1986) Effects of suspended sediments on geochemical processes near the mouth of the Amazon river - examination of biological silica uptake and the fate of particle-reactive elements. Cont Shelf Res 6 107-125... 

Winters and Lee134 describe a physically based model for adsorption kinetics for hydrophobic organic chemicals to and from suspended sediment and soil particles. The model requires determination of a single effective dififusivity parameter, which is predictable from compound solution diffusivity, the octanol-water partition coefficient, and the adsorbent organic content, density, and porosity. 

Atmosphere Water Soil Sediment Suspended Sediment Fish... 

The following assumptions apply. The air fugacity is defined and is not affected by the water or sediment processes. Common fugacities apply to (i) the air, air particles and rain (f.), (ii) to water,suspended sediment in the lake and flowing from it(f ), and to the inflow water and suspended sediment f ). If fish concentrations are to be included, they can be calculated as fyZg, but the amount in fish is considered negligible. 

FISH a SUSPENDED SEDIMENT IN EQUILIBRIUM WITH WATER... 

Subscripts are - A air, W water, S sediment, P suspended sediment, B biota. 

The evaluative lake environment is similar to the "unit world" described by Mackay and Paterson (2), consisting of a 1 km square area with an atmosphere 6000 m high, a water column 80 m deep (the approximate depth of Lake Michigan) containing suspended solids (5 parts per million by volume) and biota (considered to be fish) of 1 ppm by volume, and underlain by a sediment 3 cm deep. The bottom sediment contains 4% organic carbon and the value for suspended sediment was arbitrarily selected as ten times these bottom sediment values reflecting the enhanced sorption discussed by O Connor and Connally (14). 

The Level I calculation (Fig. 3) suggests that the dominant compartment is sediment which contains 57% of the chemical, followed by air (25%), water (10%) and suspended sediment (7%). 

Recent studies provide evidence for rapid dermal absorption of inorganic lead in adults however, these studies have not quantified the fraction of applied dose that was absorbed (Stauber et al. 1994). The quantitative significance of the dermal absorption pathway as a contributor to lead body burden remains an uncertainty. In children who experience extensive dermal contact with lead in soil, sand, or surface water and suspended sediment (e.g., beach or shoreline exposure scenario), even a low percent absorption... 

The Qwasi model estimate the fate of a chemical in a water system (lake, river, etc.) consisting of water, bottom and suspended sediments, and air. The model is... 

The Level II calculation includes the half-lives of 17 h in air, 170 h in water, 550 h in soil and 1700 h in sediment. No reaction is included for suspended sediment or fish. The input of 1000 kg/h results in an overall fugacity of 6 x 10 6 Pa, which is about 20% of the Level I value. The concentrations and amounts in each medium are thus about 20% of the Level I values. The relative mass distribution is identical to Level I. The primary loss mechanism is reaction in air, which accounts for 802 kg/h or 80.2% of the input. Most of the remainder is lost by advective outflow. The water, soil and sediment loss processes are unimportant largely because so little of the benzene is present in these media, but also... 

Suspended sediment (5) 2.977E-02 9.355E-07 7.307E-05 4.871 E-05 7.307E-02 7.307E-05... 

Suspended sediment (5) 170 1.214E+02 2.977E+01 1.859E-07 5.921 E-05 1.452E-05 7.373E-06... 

Dissociation const, pKa 4.74 Suspended sediment/water 1.38E+04 ionic 8.817... 

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