Riverine particulate material

Table 3 A comparison of the concentration of major elements in average riverine particulate material and surficial rocks...

The Cu concentration of crustal rocks (32 34 p,g g ) is approximately equivalent to that for average soils (25 4 p,g g ). However, as the earth material is weathered and transported to streams-lakes-shaUow marine sediments there is a minimal enrichment in Cu concentration (39 = 34 = 43 p,g g ) (Table 4). And, as for Pb-Zn-Cd, riverine particulate matter is greatly enriched (100p,gg ) relative to the other sedimentary materials. While the Pb-Zn-Cd concentrations of deep-sea clay are enriched 1.5 times that of the continental sedimentary materials, Cu is enriched approximately five times. The substantial enrichment of Cu in oceanic pelagic clay relative to terrestrial earth materials is due to the presence of ubiquitous quantities of ferromanganese oxides in surficial ocean sediments (Drever, 1988). 

The Ni concentration of crustal rocks (58 53 p,g g ) is substantially greater than the average world soils (23 3 p,g g ), but essentially equal to continental sedimentary materials (49 13 p,gg ). Riverine particulate matter (90p,gg ) is nearly twice the Ni concentration of these continental sedimentary materials and deep-sea clay is nearly three times (230 p-g g ) that concentration. As noted for Cu, the substantial Ni enrichment of deep-sea clays is due to the presence of ferromanganese micronodules in the oxidized surficial sediment column (Drever, 1988). 

Aggregation of dissolved humic substances can also occur with particulate materials in the estuarine water column. Preston and Riley (1982) showed that the adsorption of riverine humic substances onto kaolinite, montmorillonite, and illite increased with increasing salinity and dissolved humic substance concentration. Adsorption increased in the order kaolinite < illite < montmorillonite, which they ascribed to increasing cation-exchange capacity of the clays. They found considerable quantitative differences between the extent of adsorption of riverine versus extracted sedimentary humic substances, indicating the importance of using materials of proper origin in experiments of this type. 

The titrimetry approach is subject to a number of possible interferences. For example, in aqueous samples that are enriched in particulate material (riverine, estuarine, sewage) filtration is recommended (typically through a 0.45 pm membrane filter) to remove any particulate surfaces that might contribute to the solution alkalinity. In addition, aqueous samples that contain high concentrations of surfactants (e.g., industrial, sewage) may need longer pH electrode equilibration times during the alkalinity titrations. 

The rivers play a major role in the transfert of carbon and mineral nutrients from land to the sea and influence significantly the biogeochemical processes operating in coastal waters. Quantification of the material transport, both in the dissolved and particulate forms, has been attempted by several authors in the past (Clarke, 1924 Holeman, 1968 Garrels McKenzie, 1971 Martin et al., 1980 Meybeck, 1982 Milliman Meade, 1983). Depending on the type of sampling techniques and methods of calculations employed there are differences in the reported fluxes. A major problem in such calculations is the paucity of reliable data from some of the major rivers of the world especially of Asia (see e.g. Milliman Meade, 1983). Additionally the difficulty of obtaining representative samples from the rivers will adversely affect flux calculations. Most of the inferences drawn on the nature and transport of riverine materials rest on data collected randomly - at different points in time and space. Seasonal variations in the transport of materials are very common in some of the major world rivers, and in some cases more than 60 % of the material transport occurs within a very short period of time. Furthermore, available data are not always comparable since the analytical techniques used differ from river to river. 

The range of riverine suspended particulate matter that may be solubilized once it enters the marine realm (e.g., the so-called reactive-F ) is derived from three sources. Colman and Holland (2000) estimate that 45% may be reactive, based on RSPM-P compositional data from a number of rivers and estimated burial efficiency of this material in marine sediments. Bemer and Rao (1994) and Ruttenberg and Canfield (1994) estimate that 35% and 31% of RSPM-P is released upon entering the ocean, based on comparison of RSPM-P and adjacent deltaic surface sediment phosphorus in the Amazon and Mississippi systems, respectively. Lower estimates have been published (8% Ramirez and Rose (1992) 18% Froelich (1988) 18% Compton et al. (2000). Higher estimates have also been published (69% Howarth et al. (1995). 

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