Fluvial Input

Surface water enrichment is the result of aeolian and fluvial inputs, which are thought to be the most important sources of Th to the ocean. Thorinm-232 has been proposed as a link between the radiogenic thorium isotopes and trace metals and anthropogenic pollutants. " While the pathways are very different for the radiogenic thorium isotopes, Th is delivered to the ocean in a fashion similar to many pollutants and trace metals. For example, Guo et found Th distributions in the Gulf of Mexico and off Cape Hatteras in the North Atlantic Ocean agreed well with the general distribution pattern of aluminum. 

A survey of available Th data for the ocean basins demonstrated that the highest concentrations are found nearer to the coasts, and it was concluded that while eolian inputs likely dominated the budget in the open ocean and could account for increases near the coast, fluvial inputs may be more important in coastal regions. This implies that some a mechanism causes recycling of Th that has been removed to estuarine sediments (Huh et al. 1989). A study of an ice-covered region of the western Arctic Ocean found that significant amounts of °Th and Th were advected into the basin (Edmonds et al. 1998). Therefore, it appears that while long-lived Th isotopes are rapidly removed into estuarine sediments, transport into the ocean basins may continue. 

Figure 11 Changes in water ehemistry in Lake Balkash as a funetion of distanee from fluvial input of the Hi River. Precipitation of calcite causes Ca/Mg to decrease as waters become more evaporatively concentrated (after Versilin...

Yunker MB, MacDonald RW, Fowler BR, Cretney WJ, Dallimore SR, McLaughlin FA (1991) Geochemistry and fluxes of hydrocarbons to the Beaufort Sea shelf A multivariate comparison of fluvial inputs and coastal erosion of peat using principal components analysis. Geochim Cosmochim Acta 55, 255-273. 

The fluvial input of dissolved and suspended material to the ocean presents a boundary condition, which can reliably be estimated (cf. Fig. 1.2). Apart from eolian particle transport, which may be of great importance in areas adjacent to the great desert regions, this mode of transport represents the major pathway of element... 

Basically, sedimentation rate decreases with increasing distance from the sediment source. Since for terrigenous sediments fluvial input is the major source sedimentation rate decreases with distance from river mouth and/or coast. The... 

Figure 3 Concentrations of dissolved metals in the Humber Estuary as a function of salinity in winter with high fluvial input (solid symbols) and spring with reduced fluvial input (open symbols) (A) cadmium (B) total mercury (C) lead.

The Susquehanna River fluvial input of atrazine in the Upper Bay region is 1,700 kgtyr (8). The Chester and Choptank Rivers discharge proximately 100 kgtyr. Both contributions yield a total surface flux of 1,800 kg/yr into this region. To estimate the amount of atrazine introduced as groundwater inflow. 

However, even the dissolved freshwater metal inputs are geochemically scavenged in the mixing zone of each sub-estuary (5,22), so that in this regard, the fluvial inputs represent maximum input to the open waters of the Inland Bays. In contrast, atmospheric deposition represents direct, predominantly dissolved (i.e., readily-assimilated) inputs to surface photic zones. 

---