Continental runoff

UV absorption and fluorescence, leads to an enhancement of microbial decomposition and remineralization, whereas photodegradation of DOM with minimal CDOM has no net effect or reduces subsequent microbial decomposition and remineralization. Continental runoff is rich in CDOM, and photodegradation results in substrates that enhance microbial decomposition and the remineralization of terrestrial DOM (Miller and Moran, 1997 Smith and Benner, 2005). Very little CDOM in the open ocean appears to be of terrestrial origin (Hernes and Benner, 2006), and the photodegradation of surface water DOM results in a reduction in microbial decomposition, whereas photodegradation of deep water DOM results in an increase in microbial decomposition (Benner and Biddanda, 1998). 

Vorosmarty, C. J., K. Sharma, B. Fekete, A. H. Copeland, J. Holden, J. Marble, and J. A. Lough. 1997a. "The storage and aging of continental runoff in large reservoir systems of the world." Ambio 26 210-19. 

Peucker-Ehrenbrink B. and Blum J. D. (1998) The effects of global glaciation on the osmium isotopic composition of continental runoff and seawater. Geochim. Cosmochim. Acta 62, 3193-3203. 

Figure 8.1. Strontium input (moles) versus Sr/ Sr required to explain the enhancement observed by Martin and Macdougall [1] in foraininifera across the K/T boundary. The Sr/ Sr ratio of modem continental runoff is indicated by the arrow...

As shown by equation 20, the phosphorus concentration dissolved in the sea is controlled by (1) the upwelling rate of deep seawater, (2) the fraction of particles falling to the deep sea that survive oxidation, (3) the phosphorus content of average river water, and (4) the rate of continental runoff. 

The distribution pattern of heavy metals in surface marine sediments is regulated not only by their concentrations, but also by their physical-chemical characteristics, mineralogical composition, grain size distribution, organic matter contents, etc. Several environmental conditions such as marine currents, wind, and continental runoff must also be considered (38). Some data on trace metals in Antarctic sediments have been published, but the information available for Potter Cove is limited (27, 39- 2). 

The 20 largest rivers on Earth carry about 40% of the total continental runoff, with the Amazon alone accounting for about 15% of the total. These rivers give the best indication of global average riverwater chemical composition, which can be compared with average continental crust composition (Table 5.1). Three features stand out from this comparison ... 

The surface runoff from the World s land plays an important role in the global carbon mass exchange. The continental runoff supply of HCO is 2.4 x 10 tons/year, that is, 0.47 x 10 tons/year for carbon. Besides, the stream water contains dissolved organic matter at 6.9 mg/L, which makes up to an annual loss of 0.28 x 10 tons/year. The average carbon concentration of suspended insoluble organic matter in the stream discharge is 5 mg/L, which gives the loss of about 0.2 x 10 tons/year. Most of this mass fails to reach the open ocean and becomes deposited in the shelf and the estuarine delta of rivers. We can see that equal amounts of Cc and Co (0.5 x 10 tons for each) are annually lost from the World s land surface (Dobrovolsky, 1994). 

The species Si02(aq) may be taken as a measure of dissolution and weathering of silicate minerals in the surficial zone of the continental crust, but the same does not apply to other dissolved constituents of continental runoff. All the major cations (Ca2 +, Mg2+, Na +, and K + ) originate from different rock types and in... 

Bice K.L., Barron E.J., Peterson W.H. (1997) Continental runoff and early Cenozoic bottom-water sources. Geology 25, 951-4. 

Another pathway whereby tritium enters the ocean is through continental runoff and river flow. Tritium deposited to the continents ultimately flows to the oceans via lakes, rivers and groundwater flow, but is retained within the continental hydrosphere for time-scales of many years, thereby introducing a delayed input to the oceans. Further, when computing the time-evolving tritium inventory within an ocean basin, it is necessary to consider inflow and outflow across the basin s boundaries. 

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