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U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 1 of 3--Contamination From Hard-Rock Mining, Water-Resources Investigation Report 99-4018A

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Aquatic Physical Habitat and Hydrology in Abandoned Mined Land Studies

By Robert T. Milhous

This report is available in pdf format (no figures available): pdf milhous.pdf 62KB


Abiotic and non-chemical factors may limit the ability of a stream to respond to improvements in traditional water quality parameters because physical habitat and sediment characteristics may also limit the populations of aquatic animals. A reach of the Upper Animas River in southwestern Colorado is analyzed to show possible limits caused by physical habitat and sediment. Habitat for trout in the Animas River near Howardsville may be limited by high streamflows (because of high velocities) and by winter conditions (by velocities too high for winter habitat needs and low depths). The characteristics of the substrate (bed material) may offset the impacts of high velocities in the spring and the depths and velocities in the winter. The characteristics of the sediment in the river limit the winter habitat. In the river below Howardsville, large rocks provide shelter to trout during winter and spring runoff; fewer velocity shelters are available above Howardsville. Spawning gravels are available in the river below Howardsville but these gravels occur above the water surface of the fall spawning flows, but would be covered by spring spawning flows. Taken as a whole, it is expected the numbers and sizes of the fish would be larger below Howardsville than above if the number and size of velocity shelters is the only factor limiting fish populations. If the location of the spawning gravels is also a limiting factor, then the river spawning fish would be spring spawners, such as cutthroat trout. There are beaver ponds upstream of Howardsville that may provide fall spawning habitat for brook trout. An informal goal for the Upper Animas River is to establish a brown trout fishery. This is not a desirable goal because: (1) brown trout require that 50-70% of the river be pools and that the river must be shaded, however, there are few pools in the subject reach; and (2) brown trout spawn in the fall but the spawning gravels are high in the cross section where they can only be used by spring spawners. The existing Animas River requires a trout that can use the substrate in the main channel as habitat during most of the year. The trout most adapted to a river with few pools and gravel/cobble/rubble substrate is the brook trout. Cutthroat trout could also use the river because spawning gravels are available during spring runoff.

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