Case Studies The Dynamics of Watersheds

The watershed or drainage basin, at any scale, is the natural unit for the study of the relationships between the geology, the terrestrial ecosystems, and the soil cover on the one hand, and the hydrological system on the other. The scale ranges from watersheds of a few hectares to basins of huge rivers that cover large portions of continents (Johnson et al., 1968 Likens, 1985 Stallard, 1985 Velbel, 1985 Clayton, 1986 Dethier, 1986 Paces, 1986 Pavich, 

In arid areas, run-off is often the main source of the water reaching the bottom of valleys. The rivers carry a load consisting mainly of particles, and the nutrient content, N and P, is high. Throughout the world, estuaries of rivers draining arid lands, or the lakes they empty into, are incredibly rich in aquatic life. 

In wetlands, river loads originate within the organo-mineral compartment. Therefore, the rivers are rich in nutrients. But in numerous cases, especially in cold climates, the acidity of the water does not allow the development of an important aquatic biomass and wildlife. 

7-1 Discuss the nature of the physical weathering operating in each of the following environments  

7-2 In some ecosystems, such as those dominated by red alder Aldus rubra Bong.), there is a large production of HNO3. Under these conditions, where the HNO3 is the major proton donor, would you expect podzolization to occur  

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