404
JAMES E. DEACON AND W. L MINCKLEY
surrounding the Cuatro Ciénegas basin, Coahuila, were influenced in this
manner in July, 1968, with little discernible result other than temporary
turbidities.
Emphasis on floods and their direct and indirect effects may detract the
reader from the far greater importance of constant, specific influences of
everyday, or normal, current (a term used by us to embrace both net,
unidirectional flow and the turbulence within that flow). Repeated reference to this in past (and future) sections therefore will be summarized
and expanded later, emphasizing modal conditions as more important than
the extremes. The latter seem invariably stressed in works such as this
since they catch the human interest, and of course provide insight into
the ways of life of the animals under discussion.
2. Suspended Solids and Sedimentation
In rivers or lakes situated in areas of finely divided soils, under conditions of drainage from denuded basins, or sometimes persistently in shallow
windswept lakes or highly degrading streams, turbidity and sedimentation of silts have great impact on aquatic habitats and fishes. Exceedingly
high concentrations of suspended solids may physically suffocate fishes by
accumulation in the branchial chamber and on the gill filaments (Wallen,
1951; Buck, 1956). Kills of small-mouthed, riffle-inhabiting catostomids
have been recorded in nature in the United States (Black, 1949; Trautman,
1957; Minckley, 1971), and similarly of species of cyprinoids and
other groups in montane regions of India and Afghanistan (Nikolsky,
1963). Mass mortalities in the last areas were related to greatly increased
suspension of solids produced by runoff from monsoon rains, and even
a sisorid catfish, Glyptosternum reticulatum, highly adapted for life in
swift, turbid waters, died under conditions that prevailed.
Some fishes, notably a lungfish (Lepidosiren) and an eel (Pisodonophis
boro), possess body mucus that precipitates or coagulates finely divided
sediments (principally clays). Precipitation is effected as a result of
neutralization of negative charges on colloidal clays, by a rapid change
from circum-neutral to acidic in the mucus. This change occurs when
the mucus contacts water (van Oosten, 1957), and the fish moves in
a cell of clear water through fine muds that often comprise its habitat.
In addition, mucus has a lubricating effect on suspended particles, tending
to move them away from the skin or surfaces of the gills.
High turbidity tends to shade aquatic habitats and suppress development
of algae and other plants, but on the other hand, input from land is obviously necessary in the overall trophic economy of natural waters. Sedimentation of suspended solids, however, may have a detrimental effect on
JAMES E. DEACON AND W. L MINCKLEY
surrounding the Cuatro Ciénegas basin, Coahuila, were influenced in this
manner in July, 1968, with little discernible result other than temporary
turbidities.
Emphasis on floods and their direct and indirect effects may detract the
reader from the far greater importance of constant, specific influences of
everyday, or normal, current (a term used by us to embrace both net,
unidirectional flow and the turbulence within that flow). Repeated reference to this in past (and future) sections therefore will be summarized
and expanded later, emphasizing modal conditions as more important than
the extremes. The latter seem invariably stressed in works such as this
since they catch the human interest, and of course provide insight into
the ways of life of the animals under discussion.
2. Suspended Solids and Sedimentation
In rivers or lakes situated in areas of finely divided soils, under conditions of drainage from denuded basins, or sometimes persistently in shallow
windswept lakes or highly degrading streams, turbidity and sedimentation of silts have great impact on aquatic habitats and fishes. Exceedingly
high concentrations of suspended solids may physically suffocate fishes by
accumulation in the branchial chamber and on the gill filaments (Wallen,
1951; Buck, 1956). Kills of small-mouthed, riffle-inhabiting catostomids
have been recorded in nature in the United States (Black, 1949; Trautman,
1957; Minckley, 1971), and similarly of species of cyprinoids and
other groups in montane regions of India and Afghanistan (Nikolsky,
1963). Mass mortalities in the last areas were related to greatly increased
suspension of solids produced by runoff from monsoon rains, and even
a sisorid catfish, Glyptosternum reticulatum, highly adapted for life in
swift, turbid waters, died under conditions that prevailed.
Some fishes, notably a lungfish (Lepidosiren) and an eel (Pisodonophis
boro), possess body mucus that precipitates or coagulates finely divided
sediments (principally clays). Precipitation is effected as a result of
neutralization of negative charges on colloidal clays, by a rapid change
from circum-neutral to acidic in the mucus. This change occurs when
the mucus contacts water (van Oosten, 1957), and the fish moves in
a cell of clear water through fine muds that often comprise its habitat.
In addition, mucus has a lubricating effect on suspended particles, tending
to move them away from the skin or surfaces of the gills.
High turbidity tends to shade aquatic habitats and suppress development
of algae and other plants, but on the other hand, input from land is obviously necessary in the overall trophic economy of natural waters. Sedimentation of suspended solids, however, may have a detrimental effect on