Watershed processes runoff

One major difficulty in assessing the accuracy of any transport simulation method is the inaccuracy in runoff estimations. The basin selected for the study described was of minimum size for application of the Stanford watershed model. This is reflected in the corresponding uncertainties in all computations. However, it is worth noting that the measured and simulated concentrations of Sr and 137Cs seldom differed by more than a factor of two. This observation suggests that increasing the accuracy of simulated runoff processes will result in an increased accuracy in radioaerosol transport estimates as well. 

Whereas higher nitrate concentrations in surface (compared to bottom) waters reflect NO3 sources in watershed runoff, higher concentrations of NH4 in bottom waters derive from recychng processes occurring in the aphotic sediments (Fig. 18.6 Kemp and Boynton, 1992). Seasonal variations in bottom water NH4... 

The recovery, processing, and transport of petroleum hydrocarbons have also resulted in spillage or pollution in both freshwater and coastal wetlands. Although much attention to oil pollution in wetlands has been associated with major spills, chronic continuing input from munici-pal/industrial sources and storm water runoff from urban areas are also sources of petroleum hydrocarbons and other toxic organics to drainage and watersheds that ultimately empty into wetlands. 

All of these surface water systems are intercormected, both among themselves and with the land areas from which they receive runoff from precipitation. The watershed, or catchment, of a particular surface water body is that area which drains to the surface water body. Sizes of catchments may vary from a fraction of a square kilometer for a small pond to substantial portions of entire continents for oceans. It cannot be overemphasized that each individual water body is an ecosystem whose functioning depends not only on interactions of chemical, physical, and biological processes internal to the ecosystem but also on interconnections with the surrounding land area, the groimdwater, and the atmosphere. 

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