Arkansas River ecosystem

Category: Inland Aquatic Biomes.

Geographic Location: Western region of North America.

Summary: The Arkansas River watershed is the largest river basin in the lower Great Plains region of the United States, providing habitats for a large number of algal, plant, and animal species, as well as human settlement and use.

The Arkansas River basin and the Red River basin collectively drain a large portion of the southern Great Plains region of the United States. The region drained by the Arkansas River is the western Mississippi River basin, south of the area drained by the Missouri River and its tributaries. This region includes all of Oklahoma, most of western and central Arkansas, parts of northeastern New Mexico, Colorado, Kansas, northern and western Texas, and western and central Louisiana.

The Arkansas River begins in central Colorado in extremely rugged, high-elevation terrain, dropping almost exactly 2 miles (3.2 kilometers) from there to the point where the Arkansas River joins the Mississippi River. All the major rivers of the southern Great Plains region drain primarily from northwest to southeast and are considered to be tributaries of the Mississippi River. Along its path, the Arkansas River passes through many types of terrestrial habitats, climates, and types of human land use.

Vegetation

The river passes through six terrestrial ecoregions: the Western Short Grasslands, the Central and Southern Mixed Grasslands, the Central Forest Grassland Transition Zone, the Ozark Mountain Forests, and the Mississippi Lowland Forests.

Vegetation across the Arkansas River basin varies tremendously. There are coniferous forests in the higher elevations of the Rocky Mountains; short native grasslands in the western regions; mixed to tallgrass prairies farther to the east of the basin; deciduous forests on the slopes of the Ozark Mountains; and relatively dense Coastal Plain forest in eastern Arkansas close to the Mississippi River.

Climate

Climate varies tremendously along the Arkansas River, which is not surprising, since it moves from high elevations in the Rocky Mountains to the lowland areas of eastern Arkansas. At its headwaters in central Colorado, winters are cold and summers are cool with low humidity—while in the eastern regions of the basin, the climate is warm-subtropical, with hot, humid summers, and mild winters with rare extreme cold events. From Colorado through western Kansas, there is usually less than 20 inches (50 centimeters) of precipitation per year, but as the Arkansas River flows through Kansas and Oklahoma, it crosses into areas that experience much greater amounts of precipitation, passing 40 inches (100 centimeters) per year in northeastern Oklahoma. In the extreme eastern end of the basin in Arkansas, rainfall is greater than 50 inches (125 centimeters) per year.

The highly variable climate exhibited in the Arkansas River basin inevitably influences the type of land use that can be practiced in any given area of the basin. Human land uses are governed principally by the amount of annual precipitation, which varies considerably from west to east across the basin. In the west, Colorado grasslands dominate and are used as grazing lands for cattle, being too dry for most other types of agriculture. Moving east into Kansas, increasing annual precipitation permits wheat to be grown; this crop dominates the landscapes of Kansas. In Oklahoma and Arkansas, row crops and livestock pasture are widespread in the river valleys, with the surrounding hills and mountains covered by forests.

The entire region, with the exception of a handful of major cities (Pine Bluff, Little Rock, and Fort Smith, Arkansas; Muskogee and Tulsa, Oklahoma; and Wichita, Kansas), is primarily rural with very little heavy industry and only relatively localized mining operations. The U.S. Department of Agriculture (USDA) estimates land use outside of urban areas in this region as 50 percent rangeland and 50 percent cropland in the western areas of the Arkansas River basin; and 50 percent forest, 15 percent cropland, and 25 percent pasture in the eastern parts of the basin.

The Arkansas River has a high mean discharge of 1,313 cubic feet per second (1,004 cubic meters per second); however, the flow is highly variable along the length of the river. At certain times, the upper main stem, characterized by rocky bottoms and woody snags, lacks flow completely, and the mid- and downstream regions are wide, shallow, and have mud or sand bottoms. When exposed to full sun during low water flow conditions, water temperatures may reach 104 degrees F (40 degrees C). Thus, the Arkansas River and other rivers in the Southern Great Plains are excellent examples of extremely hot and harsh aquatic habitats.

Aquatic Life

Because the Arkansas changes significantly along its length in terms of flow, chemistry, and type of bottom substrates, it traverses four major freshwater ecoregions: Southern Plains, Central Prairie, Ozark Highlands, and Mississippi Embayment. Consequently, the aquatic communities vary greatly throughout the reaches of the Arkansas River, depending on the depth, bottom type, chemistry, flow rate, and temperature. In the headwaters of the river, the productivity of the system is likely dominated by the availability of rocky substrates, and the relatively clear water here may be nutrient-limited. In contrast, much farther downstream the river is larger and more turbid, which likely limits photosynthesis to the upper region of the water column and processes associated with hard bottom substrates are not very important. Insect, crustacean, and mussel assemblages vary depending on the part of the river examined.

The nonnative zebra mussel has invaded the river via barges in the navigation channel of the lower part of the river. Another threat is nutrient runoff from farm fertilizer; the USDA, through its Natural Resources Conservation Service, has launched a series of efforts to help farmers reduce soil erosion, trap nutrient runoff, improve water quality, and protect wildlife species and habitats.

The Arkansas River has 141 native fish species and approximately 30 nonnative fish species. Other vertebrates include several frog species; a variety of turtle species (e.g., common snapping turtle, false map turtle, yellow mud turtle); northern water snake; and numerous riparian bird and mammal species including herons, kingfishers, beaver, muskrat, and the North American river otter. The river otter is an Oklahoma state species of special concern; its numbers are on the rise, possibly because of stocking programs. The nonnative nutria is increasing in Arkansas; this species has been introduced and its numbers are growing in this region. The interior least tern, a bird species listed on the Federally Endangered Species list, has breeding populations on nonvegetated beaches and sandbars of the Arkansas River.

Human Populations

Humans were living in the Arkansas River basin by 11,500 to 10,000 years ago; these people were hunter-gatherers, pursuing the large mammals of the last ice age. By 900 years ago, major human settlements arose in the fertile river valleys in eastern Oklahoma and neighboring Arkansas. Major mound-building cities also arose in this region, such as Spiro Mound near the Arkansas River in eastern Oklahoma. In the western regions, humans hunted bison and farmed along several tributaries of the Arkansas and Red Rivers. By the mid-1500s, Spanish explorers such as Francisco Vásquez de Coronado and Hernando de Soto claimed the region for the Spanish empire. These Europeans reported large populations of Native Americans along the Arkansas River at this time, and the villages were fortified. In the western regions of the Arkansas River basin, nomadic tribes such as the Kiowa, Comanche, Arapaho, and Cheyenne lived on the plains. The release of horses by the Spanish gave these native human populations increased mobility and changed their way of life substantially.

By the early 1700s, many French explorers, trappers, and traders arrived in the Southern Great Plains region, and made contact with the native peoples in the region. Spain was acknowledged as the owner of the region by treaties in 1762-63, but Spain transferred the ownership of “Louisiana” to France in 1800–02. In the Louisiana Purchase of 1803, the United States acquired most of the Arkansas and Red River basins, together with the Missouri and western Mississippi River basins.

Among the major waterways of the southern Great Plains, the Arkansas River is unique because it is most influenced by snowmelt from the Rocky Mountains, and it traverses perhaps more diverse landscapes than any other river in this region. During most of the time of European settlement along the Arkansas River, the main river remained mostly untouched. However, in the latter half of the 1900s, major changes took place. Numerous large dams were constructed, and greater water withdrawals occurred in the western half of the Arkansas River basin. Depletion of water in the main river channel in western Kansas has been severe; this loss of water undoubtedly has had undocumented negative impacts on the animals and plants of the Arkansas River in that region. The effects may be exacerbated by drought and by more extreme seasonal temperatures as part of climate change.

Bibliography

Benke, Arthur C. and Colbert E. Cushing, eds. Field Guide to Rivers of North America. Boston: Elsevier/Academic Press, 2010.

Brown, Arthur V. and William J. Matthews. “Stream Ecosystems of the Central United States.” In Colbert E. Cushing, Kenneth W. Cummins, and G. Wayne Minshall, eds. River and Stream Ecosystems of the World. Berkeley: University of California Press, 2006.

Matthews, William J., Caryn C. Vaughn, Keith B. Gido, and Edie-Marsh-Matthews. “Southern Plains Rivers.” In Benke, Arthur C. and Colbert E. Cushing, eds. Rivers of North America. Boston: Elsevier/Academic Press, 2005.

Pierson, S. T., et al. “Phosphorus and Ammonium Concentrations in Surface Runoff From Grasslands Fertilized with Broiler Litter.” Journal of Environmental Quality 30, no. 5 (2001).