Northwestern Great Plains Intermittent Stream
Provisional State Rank
(see reason below)
State Rank Reason
The number of quality occurrences in the state is unknown, but probably fairly common. This is a difficult community type to quantify given the past years of drought in the state and the tenuous nature of this aquatic system. Intermittent pools containing the Ostracoda group should be inventoried for unique crustaceans, such as fairy or tadpole shrimp.
This ecological system is widely distributed throughout the coulees, small streams (1st to 3rd order) and headwaters of Medium Prairie Rivers (B005) and Great Plains Prairie Streams (C005) within the Northwestern Great Plains Ecoregion. These are small, warm-water, low to moderate gradient and elevation (900-1200m) intermittent streams. Stream sections in the moderate gradient reaches (riffles/runs) are the first to lose flowing water connections and become interrupted pools (D005). Once these systems lose their connectivity to fish recruitment pools of downstream reaches (this may be due to climatic factors such as prolongued drought) they become fishless isolated pools (E005). Throughout their range, these clear to turbid streams are characterized by short to long (~2-25m) pools that are sometimes vegetated with silted gravel to cobble substrates. The fishless pool community type provides substantial amphibian breeding and rearing habitat in otherwise harsh, dry upland conditions, so Bufo spp. (toads), Boreal Chorus Frogs (Pseudacris spp.), Tiger Salamanders (Ambystoma tigrinum), and Rana pipiens (northern leopard frog) tadpoles and adults are usually present. The E005c is a prairie stream reach within 1 river mile of a confluence with a larger river (at least 2 stream orders larger) and contains a biological fish community that is significantly effected by the large river connectivity.
The E005 ecological system type will be fishless. Intermittent stream pool indicator species rely on seasonal pools as essential habitat. These species, sometimes also referred to as obligate species, are dependent upon these unique pools for their continued existence. One of the defining characteristics of the seasonal pool biotic community is a lack of permanent populations of predatory fish. Isolation and periodic drying keep predatory fish from colonizing and occupying the pool. This reduced-predator environment allows amphibian larvae and invertebrate larvae to thrive. Different species of amphibian and invertebrate seasonal pool indicator species occur across the Northern Great Plains Steppe of the United States. In Montana and northwestern North and South Dakota, amphibian indicators include Woodhouse’s toad (Bufo Woodhousii), boreal chorus frogs, spadefoots (Spea bombifrons) and tiger salamanders (Ambystoma tigrinum). These amphibians depend upon seasonal pools for optimal breeding. Additionally, a crustacean group, the fairy shrimp, Branchinecta and Eubranchipus, the clam shrimp Caenestheriella, and the tadpole shrimp Lepidurus rely on these pools for their entire life cycle. The diagnostic community of intermittent prairie stream invertebrates consists of the Prairie Pool assemblage (#12, Stagliano 2005). The community indicator species are characterized by tolerant, damselfly taxa (Coenagrion/Enallagma, Lestes and Ishnura), the crustaceans (Hyalella and Gammarus), many genera and species of the water boatman (Corixidae: Sigara alternate, Trichocorixa nais, and Corisella), the snails (Physella, Gyraulus, and Stagnicola), mayflies (Caenis and Callibaetis), and beetles (Oreodytes, Laccophilus, Hydroporus and Hygrotus). As the complexity of the pool habitat decreases the clinger habitat species are lost, such as the damselflies and many of the water boatman taxa.
In Montana, the Northwestern Great Plains Intermittent Stream Ecosystem occurs throughout the non-glaciated Great Plains regions of northern North America within the Missouri and Mississippi River Drainages. Within Montana, this community exists in a multitude of streams and coulees mostly situated south of the Missouri River and within the Yellowstone River basin. Some of the many examples include Upper Otter, Bear, Hanging Woman, Trail, East Fork Trail, East Fork Hanging Woman, and Little Pumpkin Creek.
Intermittent stream pool indicator species rely on seasonal pools as essential habitat. These species, sometimes also referred to as obligate species, are dependent upon these unique pools for their continued existence. One of the defining characteristics of the seasonal (intermittent) pool biotic community is a lack of permanent populations of predatory fish. Isolation and periodic drying keep predatory fish from colonizing and occupying the pool.
Small stock ponds, dams, and cattle intrusions have had the most significant negative impact on this community. Anywhere stock ponds and dams occur the downstream reaches are affected by altered water temperatures and flow, and changes in sediment and nutrient transport (Winston et al. 1991). The spring flows backed up behind stock pond dams could have potentially filled numerous E005 pools, and possibly connected these pools for a brief period to downstream fish populations for recolonization. Therefore, unless there is sufficient outflow, streams and coulees below stock ponds usually do not develop this community type. Another threat to this community is cattle intrusions, which cause trampling of stream banks with the subsequent siltation and nutrient inputs into the pools. This siltation and nutrient loading may eliminate aquatic macrophytes and cause blue-green algae blooms.