Arkansas
Valley (Eco-Region
37)
Ecoregion 37 is a synclinal and alluvial valley lying between the Ozark Highlands
(39) and the Ouachita Mountains (36). The Arkansas Valley (37) is, characteristically,
diverse and transitional. It generally coincides with the Arkoma Basin, an
oil and gas province, that developed as sand and mud were deposited in a depression
north of the rising Ouachita Mountains during the Mississippian and Pennsylvanian
eras.
The
Arkansas Valley (37) contains plains, hills, floodplains, terraces,
and scattered mountains. It is largely underlain by interbedded Pennsylvanian
sandstone, shale, and siltstone. Prior to the 19th century, uplands
were dominated by a mix of forest, woodland, savanna, and prairie whereas
floodplains and lower terraces were covered by bottomland deciduous
forest. Today, less rugged upland areas have been cleared for pastureland
or hayland. Poultry and livestock farming are important land uses.
Water
quality is generally good and influenced more by land use activities
than by soils or geology; average stream gradients and dissolved oxygen
levels are lower in the Arkansas Valley (37) than in the Ouachita Mountains
(36) or Ozark Highlands (39), whereas turbidity, total suspended solids,
total organic carbon, total phosphorus, and biochemical oxygen demand
values are typically higher.
The
Arkansas River is continuously turbid. Summer flow in smaller streams
is typically limited or nonexistent. Fish communities characteristically
contain a substantial proportion of sensitive species; a sunfish- and
minnow-dominated community exists along with substantial proportions
of darters and catfishes (particularly madtoms).
Arkansas
Valley (Eco-Region
37)
The
Arkansas Valley (37) contains plains, hills, floodplains, terraces,
and scattered mountains. It is largely underlain by interbedded Pennsylvanian
sandstone, shale, and siltstone. Prior to the 19th century, uplands
were dominated by a mix of forest, woodland, savanna, and prairie whereas
floodplains and lower terraces were covered by bottomland deciduous
forest. Today, less rugged upland areas have been cleared for pastureland
or hayland. Poultry and livestock farming are important land uses. 
Water
quality is generally good and influenced more by land use activities
than by soils or geology; average stream gradients and dissolved oxygen
levels are lower in the Arkansas Valley (37) than in the Ouachita Mountains
(36) or Ozark Highlands (39), whereas turbidity, total suspended solids,
total organic carbon, total phosphorus, and biochemical oxygen demand
values are typically higher. 
The
Arkansas River is continuously turbid. Summer flow in smaller streams
is typically limited or nonexistent. Fish communities characteristically
contain a substantial proportion of sensitive species; a sunfish- and
minnow-dominated community exists along with substantial proportions
of darters and catfishes (particularly madtoms).