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Introduction The Fort Union Coal Formation in the Northern Great Plains can potentially provide sufficient energy at present American consumption rates for 200 to 300 years (Freeman, 1975). Recent intensive mining operations in this area have caused considerable interest in impact of coal strip mining. Although land reclamation has been of primary interest, the impact on flowing waters through the area has recently been closely observed. Several large rivers run through the formation. These include the Yellowstone River and its tributaries, the Big Horn River, Rosebud Creek, the Tongue River, and the Powder River. Because the Tongue runs through the greatest portion of the formation, it is likely to suffer the greatest impact. Indeed, with seams being at depths of two meters and the substrate of the river being a coal seam in places, the Tongue has been diverted in order to strip the original stream bed. Under the Surface Mining and Reclamation Act of 1977 (SMCRA, 1977, PL 95-87), if possible, the river must be returned to its original channel.
The Tongue River arises in the Big Horn Mountains of Wyoming and flows northeast through the Big Horn Mine at Sheridan, Wyoming into Montana where it eventually joins with the Yellowstone River (see map, Figure 1). At the Big Horn Mine, the river had been diverted into the Brown-Williams pit for several years. Within the pit, an excellent sport fishery had been established. In 1978 it was decided to return the river to its original channel configuration. With consideration of the recommendations of Wesche (1974) and Cooper and Wesche (1976), the channel was cut and graded to its approximate pre-mining configuration and gradient. Banks were hydromulched and planted with various combinations of grasses and local riparian trees and shrubs by PKS personnel (Table 1). The substrate of the new river channel contained relatively uniform layers of topsoil, gravel, and small to medium cobble (Wentworth: 32-129 mm diameter). Embankments were lined with large, angular "quarried" boulder "rip-rap" at the estimated new water line. A predicted uniform depth of 46 cm of water was to run through the new channel. At intervals along the length of the channel large boulders (up to 3 meters diameter) were placed to provide pooling and cover for potential fish colonizers. In addition, pine trees were anchored and cabled into the bank and substrate to act as "snags" to provide additional cover for fish invaders. Three sets of snags were placed in the new channel.
Thus, the construction of this new channel allowed us to examine the sources of various reclamation methods (snags, rip-rap, etc.) as well as assess the development of the benthic and fishery communities.
Additionally, the new channel allowed us to test several theories of invasion and colonization. Because the channel was reconstructed from materials not originally associated with the channel, it acted as an "island" to be colonized (or, in the case of macrobenthos, a chain of islands). This island channel allowed us to examine the equilibrium postulates of MacArthur and Wilson (1967) and in particular their application to aquatic ecosystems. Predictions of attainment of equilibrium density of benthos has varied from 14 to 21 days (Sheldon, 1977; Khalaf and Tachet, 1977) to 120 or more days (Williams and Hynes, 1977). We hoped to derive a model of benthic colonization in order to predict equilibrium attainment for a given set of circumstances. Previously, fisheries recolonization had been shown to be by young-of-the-year (Krumholz and Minckley, 1964; Gunning and Berra, 1969) and sport fish—in particular, highly territorial fish, like Centrarchids—would take several years to leave old territories to invade new areas (Larimore, Childers, and Heckrotte, 1959). Our assessment involved examination of new colonizers as well as the effectiveness of a "transplant" operation of the game fish from the Brown-Williams pit to the new river channel.
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