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<br />VII, DESERT FISHES
<br />
<br />393
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<br />Arizona, at least, severe overgrazing by domestic cattle in the period
<br />1870-1890 resulted in death of about 75% of the herd when protracted
<br />drought grasped the region in 1891-1894. Effects of this catastrophe on
<br />water and vegetation are vividly documented by paired photographs pub-
<br />lished by Hastings and Turner, which contrast the late 1800's with the
<br />present. There is little doubt that aquatic habitats, and fishes, especially
<br />those of streams, were also severely affected. The largest streams have,
<br />in addition, been subjected to channelization and stabilization of flow
<br />through impoundment (Beland, 1953; Miller, 1961a), which has essen-
<br />tially eliminated the indigenous fauna (Minckley and Deacon, 1968;
<br />Minckley, 1971), and appears to have substantially altered and decreased
<br />the value of the introduced sport fishes as well (Beland, 1953).
<br />
<br />B, SPRINGS AND MARSHES
<br />
<br />'Desert springs (Fig. 2a,b) range from swift-flowing origins of creeks
<br />(rheocrenes), to quiet, limpid pools (limnocrenes) in caves, in travertine
<br />cones, or at ground level (the last perhaps best fitting the classical concept
<br />of the oasis), and through mere trickles along canyon walls to extensive
<br />seepages into raised marshes. Larger, permanent springs in arid lands are
<br />most often positioned at points of discharge of meteoric waters along frac-
<br />ture zones, in regions of intensive, relatively recent geologic activity such as
<br />folding and faulting. Many emit thermal, magmatic waters, or meteoric
<br />water heated by contact with volcanics or by passage through the normal
<br />geothermal gradient, which in regions of relatively undisturbed, uniform
<br />rocks means a temperature increase with depth of lOC for each 15-30
<br />meters (Waring, 1965), Confined aquifers rising as springs along faults
<br />are perhaps most common. Less frequent are those flowing in the lower
<br />parts of basins just above the seal created by impervious lake beds, or
<br />at the toes of bajadas leading from montane catchments. Large, limestone
<br />springs, such as those of humid, karsted regions of many continents (Swin-
<br />nerton, 1942; Easterbrook, 1969) are rare in deserts, but a few important
<br />ones exist in arid parts of New Mexico, Texas, northern Mexico, and else-
<br />'where. These often are rcprcsented by deep sinkholes, in the bottoms of
<br />which water and aquatic organisms persist.
<br />Desert springs often are supplied from catchments located as many as
<br />a few hundrcd kilometers away, with water moving by intcrbasin transport
<br />to the dischargc point (Maxey, 1968). These types of recharge areas, or
<br />origins from deep, magmatic sources, favor relative independence of dis-
<br />charge from local patterns of precipitation. Climatic shifts do, however,
<br />result in changes in discharge of springs of meteoric origin (Haynes,
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