VII. DESERT FISHES
393
Arizona, at least, severe overgrazing by domestic cattle in the period
1870-1890 resulted in death of about 75% of the herd when protracted
drought grasped the region in 1891-1894. Effects of this catastrophe on
water and vegetation are vividly documented by paired photographs published by Hastings and Turner, which contrast the late 1800's with the
present. There is little doubt that aquatic habitats, and fishes, especially
those of streams, were also severely affected. The largest streams have,
in addition, been subjected to channelization and stabilization of flow
through impoundment (Beland, 1953; Miller, 1961a), which has essentially eliminated the indigenous fauna (Minckley and Deacon, 1968;
Minckley, 1971), and appears to have substantially altered and decreased
the value of the introduced sport fishes as well (Beland, 1953).
B. SPRINGS AND MARSHES
Desert springs (Fig. 2a,b) range from swift-flowing origins of creeks
(rheocrenes), to quiet, limpid pools (limnocrenes) in caves, in travertine
cones, or at ground level (the last perhaps best fitting the classical concept
of the oasis), and through mere trickles along canyon walls to extensive
seepages into raised marshes. Larger, permanent springs in arid lands are
most often positioned at points of discharge of meteoric waters along fracture zones, in regions of intensive, relatively recent geologic activity such as
folding and faulting. Many emit thermal, magmatic waters, or meteoric
water heated by contact with volcanics or by passage through the normal
geothermal gradient, which in regions of relatively undisturbed, uniform
rocks means a temperature increase with depth of 1°C for each 15-30
meters (Waring, 1965). Confined aquifers rising as springs along faults
are perhaps most common. Less frequent are those flowing in the lower
parts of basins just above the seal created by impervious lake beds, or
at the toes of bajadas leading from montane catchments. Large, limestone
springs, such as those of humid, karsted regions of many continents (Swinnerton, 1942; Easterbrook, 1969) are rare in deserts, but a few important
ones exist in arid parts of New Mexico, Texas, northern Mexico, and elsewhere. These often are represented by deep sinkholes, in the bottoms of
which water and aquatic organisms persist.
Desert springs often are supplied from catchments located as many as
a few hundred kilometers away, with water moving by interbasin transport
to the discharge point (Maxey, 1968). These types of recharge areas, or
origins from deep, magmatic sources, favor relative independence of discharge from local patterns of precipitation. Climatic shifts do, however,
result in changes in discharge of springs of meteoric origin (Haynes,
393
Arizona, at least, severe overgrazing by domestic cattle in the period
1870-1890 resulted in death of about 75% of the herd when protracted
drought grasped the region in 1891-1894. Effects of this catastrophe on
water and vegetation are vividly documented by paired photographs published by Hastings and Turner, which contrast the late 1800's with the
present. There is little doubt that aquatic habitats, and fishes, especially
those of streams, were also severely affected. The largest streams have,
in addition, been subjected to channelization and stabilization of flow
through impoundment (Beland, 1953; Miller, 1961a), which has essentially eliminated the indigenous fauna (Minckley and Deacon, 1968;
Minckley, 1971), and appears to have substantially altered and decreased
the value of the introduced sport fishes as well (Beland, 1953).
B. SPRINGS AND MARSHES
Desert springs (Fig. 2a,b) range from swift-flowing origins of creeks
(rheocrenes), to quiet, limpid pools (limnocrenes) in caves, in travertine
cones, or at ground level (the last perhaps best fitting the classical concept
of the oasis), and through mere trickles along canyon walls to extensive
seepages into raised marshes. Larger, permanent springs in arid lands are
most often positioned at points of discharge of meteoric waters along fracture zones, in regions of intensive, relatively recent geologic activity such as
folding and faulting. Many emit thermal, magmatic waters, or meteoric
water heated by contact with volcanics or by passage through the normal
geothermal gradient, which in regions of relatively undisturbed, uniform
rocks means a temperature increase with depth of 1°C for each 15-30
meters (Waring, 1965). Confined aquifers rising as springs along faults
are perhaps most common. Less frequent are those flowing in the lower
parts of basins just above the seal created by impervious lake beds, or
at the toes of bajadas leading from montane catchments. Large, limestone
springs, such as those of humid, karsted regions of many continents (Swinnerton, 1942; Easterbrook, 1969) are rare in deserts, but a few important
ones exist in arid parts of New Mexico, Texas, northern Mexico, and elsewhere. These often are represented by deep sinkholes, in the bottoms of
which water and aquatic organisms persist.
Desert springs often are supplied from catchments located as many as
a few hundred kilometers away, with water moving by interbasin transport
to the discharge point (Maxey, 1968). These types of recharge areas, or
origins from deep, magmatic sources, favor relative independence of discharge from local patterns of precipitation. Climatic shifts do, however,
result in changes in discharge of springs of meteoric origin (Haynes,