Irrigation-Induced Water Quality Problems (1989) / Chapter Skim
Currently Skimming:
Understanding the Scientific Dimensions of an Environmental Problem
Understanding the Scientific Dimensions of an Environmental Problem
Pages 37-52
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From page 37... ...
Chapter 3 examines the relevant institutional issues. HOW IRRIGATION DRAINAGE ALTERS WATER QUALITY Irrigation, simply defined, is the act of supplying land with water by artificial means.
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From page 38... ...
This happens because all irrigation water contains dissolved salts, and these salts are left behind as the water evaporates from the soil surface or is taken up by plants and returned to the atmosphere. If irrigation is to be maintained, adequate water must move down through the soil profile to reduce the concentration of dissolved material in the root zone.
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From page 39... ...
Highly saline drainage waters may also displace good-quality ground water. The leaching of soluble minerals from the soil and the displacement of ground water are natural processes.
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From page 40... ...
(A "mound" of water develops under the irrigation project.) On its subsurface path toward an outlet and ultimate disposal or dispersal, the drainage water displaces older ground water; frequently, this ground water contains dissolved salts of geologic origin.
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From page 41... ...
This situation has added a new dimension to the problem of irrigation water management. Drainage must now be managed not only to reduce salt accumulation in the root zone and salt disposal in streams, but also to limit the toxic effects of selected trace elements contributed by the local geology.
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From page 42... ...
The confining clay layers underlying the valley's west side inhibit deep infiltration of the irrigation waters. Thus, as irrigation water was introduced from outside the valley, the level of the prevailing water table rose.
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From page 43... ...
Very likely, the San Joaquin Valley's problems with selenium would never have surfaced had it not been for human intervention. Natural drainage from the valley was provided by the San Joaquin River system, and dissolved salts, including selenium, were transported by this system through to the delta and thence to the ocean.
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From page 44... ...
EARTH'S SOURCE: National Research Council, 1976. CORE MOLTEN -ROCK RUNNIN; AND GROUND WATERS / IGNEOUS ROCKS the selenate (+6)
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From page 45... ...
Likewise in poorly drained, periodically hooded areas where parent materials are high in selenium (e.g., Kesterson NWR) under alkaline conditions, both terrestrial and aquatic vegetation may accumulate sufficient selenium to harm aquatic organisms, waterfowl, and wildlife.
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From page 46... ...
Public concern for the quality of the habitat provided at Kesterson NWR was the major force motivating cleanup efforts at that problem site and is but one example of society's increased attention to non-economic environmental values. Once again, the California example is illustrative.
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From page 47... ...
Many wildlife refuges in the arid West are, in essence, terminal points for irrigation drainage schemes. These areas often are located in closed basins with no outlet to the sea, and so water quality problems can become severe.
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From page 48... ...
PUBLIC HEALTH CONSIDERATIONS Irrigation drainage waters often contain elevated concentrations of many elements of geologic origin, as well as agricultural chemicals. When the presence of elements of concern results in potential direct or indirect exposure of humans, a public health concern may arise.
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From page 49... ...
Studies initiated on behalf of the San Joaquin Valley Drainage Program on human health concerns associated with selenium in or near the Kesterson Reservoir indicated that there was no basis for serious alarm in that region (Klasing and Pitch, 1988~. That does not mean, however, that there is no reason for further study of selenium uptake into food plants from irrigation water in other areas.
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From page 50... ...
The historic conversion of wetlands and wildlife habitats to agricultural and other uses compounds the need to protect the remaining natural areas and to ensure an uncontaminated water supply for state and federal refuges and other wetlands. The discovery of selenium poisoning in Kesterson NWR raises the question of whether similar problems are occurring elsewhere.
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From page 51... ...
1988. Agricultural drainage water contamination in the San Joaquin Valley: A public health perspective for selenium, boron, and molybdenum.
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From page 52... ...
1986. An Agricultural Dilemma: Drainage Water and Toxics Disposal in the San Joaquin Valley.
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