Montana Field Guide

This ecosystem is found in the foothills and valleys of the Middle Rockies Ecoregion east of the Continental Divide. Elevation is 1200-2000m. These medium to large (average wetted width from 2-15m, average summer temperature <15°C) rivers have moderated permanent groundwater flow with strong seasonal variability. Waters are mineral-rich and circumneutral to alkaline with pH of 7.0-8.2; clarity is often high. These factors contribute to lush growth of submerged aquatic vegetation, which may include watercress (Nasturtium officinale), Potamogeton spp., and Myriophyllum spp.. These streams represent groundwater discharge input; therefore they do not experience severe flooding or drastic temperature shifts and have more constant flow. The substrate of these streams is usually cobble riffles and gravel/sand runs and pools, with extensive beds of aquatic vegetation and and, unless they are degraded by cattle, flow silt-free and clear.

Fish are from the Traditional Trout Stream Assemblage. The spring creek community historically had native species including westslope cutthroat, mottled sculpin, longnose dace, mountain whitefish, with Yellowstone cutthroat trout and mountain sucker in the Yellowstone drainages. However, the introduced brook, brown, and rainbow trout tend to dominate and become the focal species of these systems. Abundant populations of spring creek macroinvertebrate communities are diagnostic of this system, but diversity is relatively limited. This unique low-diversity community consists of a combination of members from the Medium Coolwater Transitional, the Traditional Trout Stream, and the Foothills Transitional Assemblages. The community is dominated by the mayflies [Tricorythodes and Ephemerella spp. (usually Ephemerella inermis and E. infrequens)], the amphipod crustacean (Gammarus), and many Chironomidae. Other community indicator species include Baetis tricaudatus, caddisfly species (Hydropsysche, Amiocentrus aspilis, Cheumatopsyche, and Brachycentrus occidentalis), beetles (Optioservus spp.), and snails (Gyraulus, Physella).

The Spring Creek type has been identified in the foothill and valleys of many Montana drainages, particularly some of the more famous trout fishing springs: Armstrong’s, Depuy’s, Nelson’s Spring Creeks of the Yellowstone and Thompson, Ben Hart (tributary to the E. Gallatin), O’Dell, Warm Spring and Big Spring Creeks of the Missouri drainage. Additionally, Layout Creek, Bridger and Piney Springs in the foothills of the Bighorns and Wyoming Basin are medium to large volume spring streams.

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Surface topography usually has a moderate gradient but can be undulating or hummocky. Disturbance by cattle is widespread, as these springs often represent the only water source in the uplands.

Spring water ecosystems are tied to climate, groundwater discharge, and water quality. Impacts to these parameters, as well as their natural variability, will have a corresponding effect on spring biological and ecological systems. Long-term drought, groundwater withdrawal at local and regional levels, and local diversions at or near the orifice are common impacts on water quantity at spring sites throughout the Western United States.

Livestock use around the riparian areas is common and can have strong local effects resulting in sedimentation and streams becoming wider or shallower. High-density cattle usage can cause severe degradation, sedimentation and siltation on the riffle habitats and gravel spawning areas downstream.