Northern Glaciated Prairie Stream
Provisional State Rank
(see reason below)
State Rank Reason
The number of high-quality occurrences in the state is unknown, but it is likely that ~50% of the original stream numbers have suffered from game fish introductions, especially northern pike. The unimpaired stream community contains northern redbelly dace and the Montana Species of Concern northern redbelly/finescale hybrid dace (S3), pearl dace (S2), and the potential Species of Concern, Iowa darter, creek chub, plains minnow and brassy minnow. The occurrence of numerous rare, threatened or declining fish and macroinvertebrate species, and consistent (e.g. water diversions, northern pike populations) or future threats (natural gas wells) warrants a state rank of S3. This ecosystem is also negatively impacted by small dams, water diversions and stock ponds. The native fish community suffers from fish introductions and community homogenization (in the far eastern Montana drainages). Because it is fairly rare to find biologically intact river miles of this ecological system the S-rank denotes this as a potential Ecological System of Concern.
This ecosystem is distributed widely throughout the Northern Glaciated Plains and Northwestern Great Plains Ecoregions. Habitats are small to medium (3rd-4th order, 30-100 river miles long, average wetted width = 6m), perennial cool/warm-water streams. In low elevation (800-1000m) areas, these are meandering streams with long runs and wide continuous pools (0.5-1.5m in depth), connected by narrow (average wetted width ~2m,) infrequently spaced riffles that may maintain connectivity throughout the year. However, riffles may be absent in incised and degraded channel sections. Substrate characteristics are typically cobble/pebble riffles (when present) to pebble/gravel runs and deeply silted pools. Side channel vegetation, undercut banks and vegetated deep pools provide the most diverse fish habitat. Woody debris is largely absent from the typical C006 and C008 stream. The C006c is a prairie stream system within 5 river miles from a confluence with a larger river (i.e,/ more than 2 stream orders larger) and contains a biological fish community that is significantly affected by its large river connectivity.
The diagnostic resident fish community is dominated by the Core Prairie Stream and the Brook Stickleback Assemblages and, in clear, vegetated, non-degraded streams, the Northern Redbelly Dace Assemblage. Without aquatic macrophytes in the pools or runs, brook stickleback or northern redbelly dace will be rare. The Creek Chub Assemblage may be present, especially near the confluence areas with a medium praire stream, C006c. A typical Northern Glaciated Prairie Stream community will have fathead minnow, lake chub (not as common), brook stickleback, northern redbelly dace, pearl dace, and brassy minnow in the vegetated pools, and white sucker, longnose dace and sometimes plains minnow, stonecat and Iowa darter in the cobble/pebble riffle and gravelly run sections. Unfortunately, northern pike has been widely introduced as a gamefish in the northern regions of Montana, and small prairie streams containing reproducing populations of these predators quickly lose their water column species, such as northern redbelly dace, pearl dace, Iowa darter, plains minnow, and brassy minnow. A fish community with the introduced pike will usually degrade to bullheads and white suckers. The Macroinvertebrate Community consists of the Large Prairie River and Prairie Stream Assemblages in the riffles, and the Medium River Side-Channel and Prairie Pool Assemblages in the slow current areas, side channels and vegetated pools. The community indicator species are characterized by the crustaceans (Hyalella and Gammarus), damselfly genera (Coenagrion/Enallagma spp. and Enallagma civile), many genera and species of the water boatman (Corixidae: Sigara grosslineata, Trichocorixa and Corisella), snails (Physella, Gyraulus, and Stagnicola) and mayflies (Caenis and Callibaetis), in the cobble riffles; and caddisflies (Hydropsyche morosa group, and Cheumatopsyche), and riffle beetles (Dubiraphia and Microcylloepus). The giant floater mussel (Pyganodon grandis) can be found in the gravel to silted side-channels since two of its host fish species are members of the Brook Stickleback Assemblage.
The Northern Glaciated Prairie Stream ecological system occurs throughout the north-central glaciated region of North America within the Missouri and Mississippi River Drainages. Within Montana this community exists in a multitude of streams such as Woody Island Coulee, upper Battle, upper Whitewater, Snake, Smoke, Beaver, People’s, Stinky, Big and Little Warm, Assiniboine, Willow, Little Cottonwood, Porcupine and Little Porcupine Creeks and the West Fork Poplar River.
Small dams, water diversions, stock ponds and introduced gamefish species have had the most significant negative impact on this community (Winston et al. 1991). Other threats include heavy cattle intrusions to the riparian areas, which causes bank erosion and subsequent sedimentation and siltation. Anywhere dams occur, even small stock pond earthen dams, the downstream reaches are affected by altered water temperatures, unnatural water level fluctuations, and changes in sediment and nutrient transport.