Northern Plains Ecoregion - National Rivers and Streams Assessment 2013-14
The Northern Plains ecoregion covers approximately 205,084 square miles, or 7% of the conterminous U.S. It includes the western Dakotas, Montana east of the Rocky Mountains, northeast Wyoming, and a small section of northern Nebraska. This ecoregion is the heart of the Missouri River system and is almost exclusively within the Missouri River’s watershed. Federal lands account for 52,660 square miles, or nearly 26% of the total area.
Human economic activity in this ecoregion is primarily agriculture, including crop production and cattle and sheep grazing. Coal mining occurs in the portions of North Dakota, Montana, and Wyoming that are within the ecoregion, and petroleum and natural gas production are growing.
This ecoregion’s terrain consists of irregular plains interspersed with tablelands and low hills. The Great Prairie grasslands were once an important feature of this ecoregion, but they have largely been replaced by other vegetation or land uses, particularly cropland. The total river and stream length represented in NRSA 2013–14 for the Northern Plains ecoregion is 27,108 miles.
The climate in this ecoregion is dry and characterized by short, hot summers and long, cold winters. Temperatures average 36°F to 46°F, and annual precipitation totals range from 10 to 25 inches. High winds are an important climatic factor in this ecoregion, which is also subject to periodic intense droughts and frosts.
The macroinvertebrate MMI showed that 50% of river and stream length in the Northern Plains ecoregion was of good quality (based on the least-disturbed reference distribution). The fish MMI showed that 35% of river and stream length was of good quality. Twenty-one percent of river and stream length was not assessed or, for various reasons, had insufficient data to calculate the fish MMI.
Chemical and Physical Habitat Indicators
The percentage of miles rated good for chemical and physical habitat indicators varied widely within the Northern Plains ecoregion. Phosphorus and nitrogen tended to have a higher percentage of river and stream miles with good quality, 40% and 47% respectively, compared to other ecoregions; but unlike other ecoregions, salinity had a higher percentage of rivers and streams rated poor. Physical habitat measures such as riparian vegetation cover and instream fish habitat showed high percentages of river and stream miles with good quality, 72% and 69% respectively.
Human Health Indicators
Human health indicators measured within the Northern Plains ecoregion showed that most of the river and stream miles were below levels of concern. Enterococci were at or below the national benchmark for 80% of river and stream length. Microcystins were at or below the national benchmark for 100% of river and stream length. Mercury in fish tissue plugs was at or below the national benchmark for 49% of river and stream length, with 40% unassessed for a variety of reasons, including the absence of fish, the lack of habitat to support fish that met the minimum size requirement, inability to obtain permits, inclement weather, and site access denial.
To access more indicator graphics please visit the interactive NRSA Dashboard.