Agroecoregions are zones having unique soil, landscape, and climatic characteristics which confer unique limitations and potentials for crop and animal production. The 9,570,000 acre Minnesota River basin was subdivided into 13 unique agroecoregions primarily upon distinctions between soil types and geologic parent material, slope steepness, natural and artificial internal drainage, erosion potential and climatic factors influencing crop productivity (click here for a map of agroecoregions). Each agroecoregion contains unique physiographic factors that influence the potential for production of non-point source pollution and the potential for adoption of farm management practices.
It is essential to note that each of the twelve major watersheds in the basin encompasses at least two and as many as six agroecoregions. One of the most diverse watersheds is the Chippewa River watershed, which encompasses six agroecoregions. The characteristics of these six agroecoregions range from steep, well drained loamy soils, to flat, poorly drained silty clay soils. Also included are flat sandy outwash soils that can support irrigation, several stream banks and steep vally walls. The variability in soils and landscapes within a watershed is important for a proper understanding of sources of non-point source pollution and the potential for adoption of various agricultural management practices.
The Minnesota River basin encompasses 27 geomorphic classes involving broad classes of soil and geologic parent material. Examples of these classes include various types of glacial outwash and alluvial material, till, moraine, and lacustrine sediment . Glacial outwash tends to occur on relatively flat landscapes with well drained sands or poorly drained loams (click here for a map). Glacial till tends to occur on flat to moderately steep landscapes with loamy to silt loam textures and a complex mixture of well drained and poorly drained soils. Glacial moraines tend to have moderate to steep slopes, loamy well drained soils. Lacustrine sediments tend to occur on flat landscapes and be poorly drained.
The top five geomorphic classes by extent of areal coverage are the Blue Earth Till Plain (30.3% of the basin), the Waconia-Waseca Moraine (9.6%), the Alexandria Moraine Complex (8.6%), the Ivanhoe- Worthington Coteau (8.2%), and the Olivia Till Plain (8.0%) (click here for a table).
The landscapes of the Minnesota River basin are complex, and have been divided into 7 slope steepness classes (click here for a map). Approximately 37.7% of the basin is covered by the 2-6% slope steepness class, 33.6% by the 0-2% steepness class, 12.1% by the 6-12% steepness class, 7.8% by the 2-12% steepness class, 7.6% by the 6-45% steepness class, and 1% by the 12-45% steepness class (click here for a table). In general, increases in slope steepness result in a greater potential for water erosion and runoff. The MRAP report recommended targeting highly erodible land for implementation of best management practices to control erosion.
There are three major hydrologic classes of internal drainage for the soils of the Minnesota River basin, including well-drained, poorly drained, and poorly drained soils improved by tiling (click here for a map). Well drained soils have faster internal infiltration until saturated, while poorly drained soils have slower internal infiltration and tend to pond water at the surface. Ponded water limits trafficability of cropped soils, and is undesirable for production agriculture. Approximately 58.2% of the basin is covered by well drained soils, while 20.9% of the basin is covered by poorly drained soils (click here for a table). Many of the poorly drained soils are tile drained. Another 20.2% of the basin is covered by soils that were improved to well drained from poorly drained conditions by installation of tile drainage systems.
Extensive subsurface tiling and surface tile inlets have been installed on poorly drained soils of the Minnesota River basin to improve the trafficability and productivity of these soils. Such hydrologic alterations have increased the peak flow of water discharging into streams and rivers of the basin, increasing the potential for bank and bed erosion. Sediments and nutrients, as well as fecal matter from barnyards, feedlots, and animal water lagoons can enter surface tile inlets and be rapidly transported into surface waterways. Tile drainage systems can also illegally carry human sewage from improperly designed residential septic tanks.
Crop productivity for the Minnesota River basin was estimated using factors such as precipitation, growing degree days, slope steepness, soil texture, soil drainage, and rooting depth (click here for table). Approximately 31.2% of the basin (towards the eastern portion of basin) has an average annual precipitation exceeding 28 inches. Growing degree days for corn range from 1500 to 2750 in the western and eastern portions of the basin, respectively. Crop productivity follows gradients in precipitation and growing degree days, and varies from low to medium in the western portion of the basin, to high in the eastern part of the basin.
Hydrologic features are important to the transport and attenuation of non-point source pollution in the Minnesota River basin. These features include lakes, permanent or intermittent streams, drainage ditches, and wetlands. Lands adjacent to waterways are generally considered to be more likely to adversely impact water quality by non-point source pollution than land set back from the waterways. In the Minnesota River basin, approximately 65.6% of the cropland is not bordered by any water, while 20.0% of the land is bordered by streams, 8.2% borders drainage ditches, and 5.7% borders lakes (click here for a table).
The MRAP report recommended targeting land adjacent to waterways for implementation of best management practices to control sediment losses. Land bordering permanent streams and rivers in the Minnesota River basin frequently has a slope steepness exceeding 6% (click here for a table). For example, of the land bordering permanent streams and rivers, approximately 33% exceeds 6% in slope steepness in the Upper Minnesota River watershed. In the Pomme de Terre River watershed, about 57% of the land bordering streams and rivers is steep, while the corresponding percentage is 36% in the Hawk Creek-Yellow Medicine watershed. In the Chippewa River watershed 63% of the land next to rivers is steep, while 20% of the land next to rivers is steep in the Redwood River watershed. In the Middle Minnesota River watershed, 11% of the land next to rivers is steep, while the corresponding percentage is 20% in the Le Sueur River watershed.
Individual units for geomorphic classification, slope steepness, internal drainage, and crop productivity were grouped into larger units with similar characterisics using a geographic information system.
The resulting 13 agroecoregions can be viewed with overlays for streams and rivers, as well as boundaries for the entire basin, major watersheds (click here for a map), or county boundaries (click here for a map). A general description for salient features of each agroecoregion is given below.
An extensive GIS database for the Minnesota River basin has been compiled. This database has been processed to provide the following information describing the characteristics of major watersheds in the Minnesota River basin and its agroecoregions. (Click here for a table with agroecoregion acreage within major watersheds)
The Steep Dryer Moraine encompasses 829,900 acres in the northern portion of the Minnesota River basin. It includes portions of Pope, Otter Tail, Grant, Douglas, Pope, Swift, and Kandiyohi counties. The northern portions of the Pomme de Terre, Chippewa, and Hawk Creek watersheds include land in the Steep Dryer Moraine (click here for a table). Much of the land adjacent to rivers is steep in this agroecoregion, producing a large potential for sediment delivery to streams. The Steep Dryer Moraine is characterized by landscapes with a complex mixture of moderate to steep slopes with 80% land having 6-45% slope steepness. A large proportion of land borders one of the many lakes that characterize this region. Soils are predominantly loamy in texture and are well drained. Approximately 84% of lands in this agroecoregion have a very high potential for erosion by water.
The Olivia Till includes 1,365,100 acres crossing portions of Grant, Stevens, Big Stone, Swift, Chippewa, Kandiyohi, Renville and Nicollet counties. Portions of the Upper Minnesota, Pomme de Terre, Hawk Creek, and Chippewa watersheds are crossed by the Olivia Till (click here for a table). Much of the land adjacent to rivers is moderately steep in this agroecoregion, producing a moderate potential for sediment delivery to streams. The Olivia Till is characterized by landscapes with moderate slope steepness, and roughly 51% of this agroecoregion has a moderate water erosion potential. Soils are mostly loams and silt loams, with roughly two thirds of these being well drained, and the remainder being tile drained. Roughly one fourth of all land in the Olivia Till is adjacent to streams or drainage ditches.
The Coteau includes 848,100 acres of land in Yellow Medicine, Lincoln, Lyon, Murray, Redwood, Pipestone, Laq Qui Parle and Cottonwood counties. Portions of the Lac Qui Parle, Yellow Medicine, and Redwood watersheds are in the Coteau (click here for a map). About one third of the land in this agroecoregion is adjacent to streams, with most of this having slopes of from 2-6% steepness (click here for a table). The Coteau is characterized by landscapes with long northeast facing slopes of moderate steepness, and 70% of the Coteau has a very high water erosion potential. Soils are predominantly loamy and well drained.
The Dryer Blue Earth Till includes 1,660,400 acres of land in Lac Qui Parle, Brown, Watonwan, Yellow Medicine, Lyon, Redwood, Cottonwood, and Jackson counties. Portions of the Upper Minnesota, Lac Qui Parle, Yellow Medicine, Redwood, Cottonwood, Middle Minnesota, and Watonwan watersheds are included in the Dryer Blue Earth Till (click here for a table). About one third of the land in this agroecoregion is adjacent to streams and drainage ditches, with most of this land having flat slopes ranging from 0-6% in steepness (Table 4). Soils are predominantly loamy, with landscapes having a complex mixture of well and poorly drained soils. Drainage in depressional areas is often poor, and tile drainage is common. Water erosion potentials in the Dryer Blue Earth Till are moderate on 79% of the land.
The Dryer Clays and Silts include 584,300 acres of land in Pope, Grant, Stevens, Big Stone, Chippewa, and Swift counties. Portions of the Upper Minnesota, Pomme de Terre, Hawk Creek, and Chippewa watersheds pass through the Dryer Clays and Silts (click here for a table). Somewhat less than one third of the land in this agroecoregion is adjacent to streams and drainage ditches, with most of the land having slopes ranging from 0-6% in steepness. Soil textures range from silty clay to silt loam, with extensive artificial drainage to correct poor internal drainage. Water erosion potentials in this agroecoregion are high on 25% of the land. Wind erosion potentials are high on 40% of the land.
The Steep Wetter Moraine includes 324,200 acres of land in Dakota, Hennepin, Carver, Scott, and Rice counties, and drainage from the Steep Wetter Moraine enters the Lower Minnesota watershed (click here for a table). This agroecoregion includes the rapidly urbanizing suburbs of the Twin Cities, where many new construction sites for houses with septic tanks are located. This agroecoregion has roughly one quarter of its land adjacent to streams and another one eighth next to lakes. Much of the land next to streams is very steep, with a large potential for sediment delivery to streams. Soil textures in this agroecoregion range from sandy loam to loam, and landscapes are primarily well drained. More than 50% of the land in the Steep Wetter Moraine has a very high water erosion potential with 16% lands having very severe and 3% lands having exteam erosion.
The Less Steep Moraine is located along the eastern boundary of the Minnesota River basin. It includes land in Carver, Scott, Le Sueur, Blue Earth, Waseca, Steele, Freeborn, and Faribault counties. Drainage from the 742,600 acres of Less Steep Moraine enters the Middle Minnesota, Blue Earth, Le Sueur, and Lower Minnesota watersheds (click here for a table). About one fourth of the land in this agroecoregion is adjacent to streams and ditches, with much of this land having slopes ranging from 2-12% steepness. About 90% lands have a very high potential for erosion. Soils in the Less Steep Moraine are primarily loamy in texture. Agricultural lands are dominated by moderately steep (2-12%) well drained portions, but roughly one third of the land is flat (0-2%) and tile drained. 50% of the cropped lands have a high potential for water erosion.
The Wetter Blue Earth Till includes 867,800 acres of land in portions of Brown, Jackson, Cottonwood, Faribault, Watonwan, Martin, and Blue Earth counties. Drainage from the Wetter Blue Earth Till enters the Middle Minnesota, Cottonwood, Watonwan, and Blue Earth watersheds (click here for a table). Approximately 20% of the land adjacent to streams and drainage ditches. Roughly three fourths of the land in this agroecoregion is not bordered by streams, lakes, or drainage ditches. Soils are primarily loamy in texture. Landscapes in the Wetter Blue Earth Till are a complex mixture of relatively flat (2-6%) well drained soils and very flat (0-2%) while 46% are poorly drained soils. Artificial drainage to remove ponded water from flat and depressional areas is extensive. Water erosion potentials are very high on 60% of the land in this agroecoregion.
The Wetter Clays and Silts include portions of Sibley, Carver, Nicollet, Blue Earth, Faribault, Waseca, Freeborn, Watonwan, McLeod, Rianville and Martin counties. Drainage from the 1,108,410 acres of Wetter Clays and Silts enters the Middle Minnesota, Watonwan, Blue Earth, Le Sueur, and Lower Minnesota watersheds (click here for a table). Roughly three fourths of the land in this agroecoregion is not bordered by streams, lakes, or drainage ditches. Landscapes are primarily flat (0-2%) and poorly drained or tile drained. This agroecoregion is subdivided into a northern section with loamy soil textures, and a southern section with silty clay or silty clay loam textures. Artificial drainage has been extensively used to improve the internal drainage of soils in the northern region. Subsurface and surface tiling are extensively used in the southern region, but internal drainage remains poor. Isolated pockets of well drained land with slopes ranging from 2-12% steepness account for roughly one fifth of all land in the Wetter Clays and Silts. Roughly 47% of the land in this agroecoregion has a moderate water erosion potential.
Alluvial and Outwash landscapes are widespread throughout the Minnesota River basin (click here for a table), with roughly one fourth of this land occurring primarily in river drainageways and the remainder occurring in the northwestern portion of the basin (Swift, Chippewa, and Pope counties). Approximately 656,000 acres of land has its origins in alluvial or outwash sediments, with a tendency for sandy and loamy soil textures. In the northwestern portion of the basin, outwash soils tend to occur on flat (0-2%) landscapes with extensive artificial drainage. Lands of alluvial or outwash origin along river drainageways are primarily 2-12% in slope steepness, and are well drained. 25% of the land in this agroecoregion has a very high water erosion potential, while 39% has a high wind erosion potential.
The Steep Stream Banks agroecoregion encompasses 112,700 acres in Blue Earth, Faribault, Martin and Brown counties. Portions of the Blue Earth, Le Sueur, Cottonwood, Middle Minnesota, and Watonwan watersheds are included in this agroecoregion (click here for a table). In fact, 94% of the Steep Stream Banks agroecoregion occurs in the Blue Earth, Le Sueur, and Cottonwood watersheds, with 63% of this agroecoregion being located in the Blue Earth watershed alone. Potential rates of erosion in the Steep Stream Banks agroecoregion are extreme in 9% of the agroecoregion, and the remainder of land in this agroecoregion has very high erosion rate potentials.
The Stream Banks agroecoregion encompasses 257,000 acres in Redwood, Yellow Medicine, Lyon, Laq Qui Parle, Stevens, Swift, Cottonwood, Grant, Brown, and Pope counties. This agroecoregion includes portions of the Cottonwood, Laq Qui Parle, Redwood, Hawk Creek, Yellow Medicine, Pomme de Terre, and Chippewa watersheds (click here for a table). About 80% of this agroecoregion lies in the Blue Earth Till Plain, and consists of loamy textured soils. Erosion potential is large, due to the proximity of lands to streams and a large sediment delivery ratio. Erosion potentials in the Stream Banks agroecoregion are not as great as those in the Steep Stream Banks or Steep Valley Walls agroecoregions.
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