Rivers particle flux

Up welling flux + River runoff flux = Downwelling flux + Particle flux (91)... 

Figure 3.5 Schematic illustration of particle fluxes in the Clyde and Humber Estuaries. Arrow size denotes relative magnitude of the flux. The broken line represents the boundary of the saline intrusion and the river. REM and MEM denote river and marine end-members, respectively. All terms are defined in the text.

The role of water column particles in capturing dissolved trace elements has been known for a long time (e.g., Schindler, 1975). The practical significance of this was demonstrated by Santschi (1984), who showed how the water column residence times of trace elements could be predicted from the particle flux. The simplest model which links fluxes of particles, supply of trace elements, and capture by sediments, is that of Schindler (1975). At the heart of the model is the distribution coefficient, (sometimes referred to as the partition coefficient), which quantifies the relationship between the dissolved and particulate concentrations. Most subsequent formulations of the model are built around this concept (e.g., Imboden et al, 1980 Diamond etal., 1990 Hilton et al. 1995 Appleby, 1997). These models all assume reversible sorption of dissolved elements to particle surfaces. This simplistic view is broadly supported by recent studies of suspended particles in rivers (Findlay et al., 1996 Ferriera et al., 1997) and more rigorous chemical models of binding (e.g.. Lofts Tipping, 1998). 

In summary, extensive research has been carried out on the lanthanide geochemistry of marine hydrothermal vent systems. Lanthanides are good indicators of water/rock reactions between hydrothermal fluids and basalt, and reactions between Fe oxide particles and seawater. While the lanthanides undergo an active geochemical cycle in and above venting fluids, this cycle is not quantitatively significant with respect to river water fluxes and oceanic cycles and inventory. 

The transfer of P from the continents to the ocean is separated into two distinct pathways. The flux of reactive P (F25) is estimated via measurements of dissolved organic and inorganic P in rivers. A small correction (33% after Kaul and Froelich, 1984) is added to the measured values to account for P released from particles within the estuaries. This P is transported directly to the surface ocean and is... 

A small flux is shown between the land and atmosphere. This represents the transport of dust particles to the atmosphere (F28) and the deposition of these particles back on land either as dry deposition or associated with atmospheric precipitation (F82). Similarly, fluxes that represent the transport of seasalt from the surface ocean to the atmosphere (Fss) and the deposition of soluble (F85) and insoluble (F81) atmospheric forms are also shown. As already discussed for the river fluxes, the insoluble particulate flux is represented as a direct transport of P to the sediment reservoir. 

The problem is to calculate the steady-state concentration of dissolved phosphate in the five oceanic reservoirs, assuming that 95 percent of all the phosphate carried into each surface reservoir is consumed by plankton and carried downward in particulate form into the underlying deep reservoir (Figure 3-2). The remaining 5 percent of the incoming phosphate is carried out of the surface reservoir still in solution. Nearly all of the phosphorus carried into the deep sea in particles is restored to dissolved form by consumer organisms. A small fraction—equal to 1 percent of the original flux of dissolved phosphate into the surface reservoir—escapes dissolution and is removed from the ocean into seafloor sediments. This permanent removal of phosphorus is balanced by a flux of dissolved phosphate in river water, with a concentration of 10 3 mole P/m3. 

Model simulations of particle volume concentrations in the summer as functions of the particle production flux in the epilimnion of Lake Zurich, adapted from Weilenmann, O Melia and Stumm (1989). Predictions are made for the epilimnion (A) and the hypolimnion (B). Simulations are made for input particle size distributions ranging from 0.3 to 30 pm described by a power law with an exponent of p. For p = 3, the particle size distribution of inputs peaks at the largest size, i.e., 30 pm. For p = 4, an equal mass or volume input of particles is in every logaritmic size interval. Two particle or aggregate densities (pp) are considered, and a colloidal stability factor (a) of 0.1 us used. The broken line in (A) denotes predicted particle concentrations in the epilimnion when particles are removed from the lake only in the river outflow. Shaded areas show input fluxes based on the collections of total suspendet solids in sediment traps and the composition of the collected solids. 

This simple two component model for the Fe isotope composition of seawater does not consider the effects of the Fe isotope composition of dissolved Fe from rivers or from rain. Although the dissolved Fe fluxes are small (Fig. 19) the dissolved fluxes may have an important control on the overall Fe isotope composition of the oceans if they represent an Fe source that is preferentially added to the hydrogenous Fe budget that is ultimately sequestered into Fe-Mn nodules. In particular riverine components may be very important in the Pacific Ocean where a significant amount of Fe to the oceans can be delivered from rivers that drain oceanic islands (Sholkovitz et al. 1999). An additional uncertainty lies in how Fe from particulate matter is utilized in seawater. For example, does the solubilization of Fe from aerosol particles result in a significant Fe isotope fractionation, and does Fe speciation lead to Fe isotope fractionation ... 

The distribution of sediment types in the Pacific Ocean is much different from that of the Atlantic. Except for the coastline of the northwest United States, the Pacific is ringed by deep-sea trenches and, hence, has relatively narrow continental shelves. The trenches effectively trap all the terrigenous particles carried to the sea by river runoff. The Pacific Ocean is much wider than the other oceans thus the flux of wind-borne lithogenous particles is spread over a much greater area and produces a much lower mass flux, on an areal basis, to the seafloor. This makes other particles relatively important in determining the composition of the sediments in the Pacific ocean. 

The overall effect of the terrestrial weathering reactions has been the addition of the major ions, DSi, and alkalinity to river water and the removal of O2, and CO2 from the atmosphere. Because the major ions are present in high concentrations in crustal rocks and are relatively soluble, they have become the most abimdant solutes in seawater. Mass-wise, the annual flux of solids from river runoff (1.55 x 10 g/y) in the pre-Anthropocene was about three times greater than that of the solutes (0.42 x 10 g/y). The aeolian dust flux (0.045 X 10 g/y) to the ocean is about 30 times less than the river solids input. Although most of the riverine solids are deposited on the continental margin, their input has a significant impact on seawater chemistry because most of these particles are clay minerals that have cations adsorbed to their surfaces. Some of these cations are desorbed... 

The high vertical flux of particulates in river/estuarine plume regions commonly results in the accumulation of particles in the formation of a benthic boundary layer (BBL) and/or mobile and fluid muds (see chapter 6 for more details). The BBL is defined by Boudreau and Iprgensen (2001, p. 1) as those portions of sediment and water columns that are affected directly in the distribution of their properties and processes by the presence of... 

---