Subsurface runoff

Subsurface runoff. When precipitation hits the land surface, the vast majority does not go directly into the network of streams and rivers in fact, it may be cycled several times before ever reaching a river and the ocean. Instead, most precipitation that is not intercepted by the vegetation canopy and re-evaporated infiltrates into the soil, where it may reside as soil moisture, percolate down to ground-water, or be transpired by plants. 

Fig. 6-7 Vertical cross-section showing pathways for surface and subsurface runoff. Path 1 HOF path 2 groundwater flow path 3 subsurface stormflow path 4 SOF. (From Dunne and Leopold, 1978.)...

The other output from watershed and slope landscapes positions is related to the surface and subsurface runoff of trace metals. The ecosystems of waterlogged glacial valleys, geochemically subordinate to the above mentioned landscape, can receive with surface runoff an additional amount of various chemical species. This results in 3 1-fold increase of plant productivity in comparison with elevated landscapes and in corresponding increase of all biogeochemical fluxes of elements, which are shown in Table 6. For instance, the accumulation of trace metals in dead peat organic matter of waterlogged valley was assessed as the follows Fe, n x 101 kg/ha, Mn, 1-2 kg/ha, Zn, 0.1-0.3 kg/ha, Cu, Pb, Ni, n x 10-2 kg/ha. 

Culley, J. L. B. and Phillips, P. A. (1982). Bacteriological quality of surface and subsurface runoff from manured sandy clay loam soil. J. Environ. Qual. 11,155-158. 

Gaynor, J.D., D.C. MacTavish, and W.L Findlay (1995). Atrazine and metolachlor loss in surface and subsurface runoff from three tillage treatments in com. J. Environ. Qual., 24 246-256. 

Rohde, W.A., L.E. Asmussen, E.W. Hauser, M.L. Hester, and H.D. Allison (1981). Atrazine persistence in soil and transport in surface and subsurface runoff from plots in the coastal plain of the southern United States. Agro-Ecosystems, 1 225-238. 

Figure 2. Conceptual scheme of a small catchment ecosystem. Fluxes of element i between a hydrological basin and its surroundings Wi, total weathering of rocks Pi, wet atmosphere deposition Di, dry deposition Ai, possible anthropogenic inputs (e.g. fertilization) Ri, surface and subsurface runoff of soluble substances Mi, possible water erosion of solid substances Bi, biomass export (harvesting) (Moldan and Cherny, 1994).

As rainfall decreases, overland flow also decreases, but subsurface runoff continues for several days after the storm as water gradually drains from the soil. This explanation assumes that three water sources of differing chemical characteristics contribute to stream flow, in contrast to the assumption of two water sources made by other authors, for example, Pinder and Jones (45). 

The hydrology and chemistry of lakes and streams are highly individualistic. Lakes surrounded by poorly buffered soil and underlain by granitic bedrock appear to be more susceptible to acidification when exposed to acid rain (Havas et al. 1984). Other lake characteristics such as dominance of atmospheric input or surface/subsurface runoff as the major source of water, type and depth of soil, bedrock characteristics, lake size and depth, area of the drainage basin, and residence time of water in the lake are all features that influence the response of a lake to acid rain. 

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