Transport by rivers

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

The material transported by rivers consists of dissolved ions (dissolved load), sediment suspended in the flow (suspended load), and sediment transported along the bed of the river (bedload). The total load and the proportion of the load represented by these phases varies widely among rivers in different environments. In particular, climate, topography, and erosion influence the amount and composition of riverine sediment loads. 

MacKenzie and Garrels equilibrium models. Most marine clays appear to be detrital and derived from the continents by river or atmospheric transport. Authigenic phases (formed in place) are found in marine sediments (e.g. Michalopoulos and Aller, 1995), however, they are nowhere near abundant enough to satisfy the requirements of the river balance. For example, Kastner (1974) calculated that less than 1% of the Na and 2% of the K transported by rivers is taken up by authigenic feldspars. 

Some of the clays that enter the ocean are transported by river input, but the vast majority of the riverine particles are too large to travel fer and, hence, settle to the seafloor close to their point of entry on the continental margins. The most abundant clay minerals are illite, kaolinite, montmorillonite, and chlorite. Their formation, geographic source distribution and fete in the oceans is the subject of Chapter 14. In general, these minerals tend to undergo little alteration until they are deeply buried in the sediments and subject to metagenesis. 

Most of the organic matter in seawater was created in situ by marine processes and is, hence, classified as autochthonous. Organic matter of nonmarine origin is classified as allochthonous and is primarily terrestrial detritus, transported by rivers or winds. The input of organic matter from rivers is small (0.4 Pg C/y) compared to primary productivity (40 to 50 Pg C/y). The aeolian input is unknown but thought to be significant. 

The products of chemical weathering, Ca, H4Si04, and 2HCOj, are transported by river runoff into the ocean, where they are then available to be returned to biogenic form by marine plankton. (Marine plankton have an enzyme, carbonic anhydrase, that converts bicarbonate to CO2.)... 

The physical transport of mass is essential to many kinetic and d3mamic processes. For example, bubble growth in magma or beer requires mass transfer to bring the gas components to the bubbles radiogenic Ar in a mineral can be lost due to diffusion pollutants in rivers are transported by river flow and diluted by eddy diffusion. Although fluid flow is also important or more important in mass transfer, in this book, we will not deal with fluid flow much because it is the realm of fluid dynamics, not of kinetics. We will focus on diffusive mass transfer, and discuss fluid flow only in relation to diffusion. 

In 1986, J.I. Hedges and colleagues (see reference) reported on how dissolved and particulate organic material transported by rivers can provide... 

As Krapivin (1995) showed, complex evaluation of the pollution level in the Arctic Basin as a whole is possible by synthesizing a mathematical model of pollutant transport by rivers from adjacent territories. 

Should the data concerning carbamazepine be of more general validity, estuarine areas, and even more the deltas because of their shallower water, could be important locations for the photochemical transformation of pollutants transported by river water. Also note that carbamazepine underwent oxidation and dimerization in the presence of Fe(III) + chloride, and chlorination only to a... 

Figure 16.2 Model-predicted latitudinal distribution in the North Atlantic Basin (a) estuarine denitrification (b) total nitrogen transport by rivers. (Modified from Seitzinger, 2000.)...

Pollutants in surface waters are transported by rivers either in the dissolved or in the particulate states, and they may later accumulate in lakes or in the estuaries into which they flow. Ocean currents can transport pollutants over long distances. 

The sources of particulate phosphorus to the seabed include detrital inorganic and organic material transported by rivers to the ocean, biogenic material produced in the marine water column that sinks to the seabed, and atmospheric... 

In natural water, trace metals can be present in the form of free ions, complexes or organo-metallic compounds. They also may be adsorbed onto particidate matter. Many phenomena affect the distribution of trace metals between dissolved and particulate forms when they enter estuaries, having been transported by rivers. The origin of these phenomena is that the metals are exposed to an environment with increasingly different physical and chemical characteristics. In order to understand the distribution, transport, bioavailability, etc., of trace metals, their physico-chemical... 

The most important flux of the freshwater phosphorus cycle is the large amount of phosphorus transported by river runoff. This flux has been esti-... 

Mud, silt and sandy sediments form mainly by weathering—the breakdown and alteration of solid rock. Usually, these sedimentary particles are transported by rivers to the oceans, where they sink onto the seabed. Here, physical and biological processes and chemical reactions (collectively known as diagenesis) convert sediment into sedimentary rock. Eventually these rocks become land again, usually during mountain building (orogenesis). 

Substance Mining production1) (million tons/yr) Transport by river to oceans2) (million tons/yr) Atmospheric washout3) (million tons/yr)... 

Weathering, atmospheric deposition, and the fixation of atmospheric gases are the ultimate sources of the material transported by rivers. These... 

The composition of dissolved and solid material transported by rivers in mountain belts of the humid... 

Garrels and Mackenzie (1971) calculated global river loads based on Livingstone s (1963) data. From these figures, Kempe (1979a) deduced the following fluxes of carbon to the oceans transported by rivers ... 

---