Land Use and Stream Ecosystems in the Ozark Highlands, Missouri and Arkansas - Extracting a Weak Signal From Background Noise

Land use history in the Ozark Highlands of Missouri and Arkansas included widespread timber harvest in the late 19th and early 20th centuries, followed by substantial depopulation that left a mosaic of land dominated by timber harvest, grazing, and other agricultural land uses. There is regional concern that present-day timber harvest and agricultural land-use practices may have detrimental effects on highly valued, biologically unique, and species-rich Ozarks streams. Our synthesis of five recent studies of landscape characteristics and stream ecosystems in the Ozarks documents scale-dependence and geographic complexities of links from land use to stream ecosystems. Over 100 study streams in the combined dataset range 6 - 4,300 km² in drainage area and drain rural land ranging 15-100% forested. Fish, aquatic insect, and periphyton communities can be reliably associated with some mesohabitat- and reach-scale measures of habitat and water quality. Biotic communities in some streams also appear linked to drainage-basin land use through controls on nutrient availability. However, physical habitat, thought to be an important factor affecting biotic community structure, is often only weakly linked to drainage-basin land use. We suggest that the weak relationships between drainage-basin land use, physical habitat, and biotic community structure in these streams is due to several interacting factors including: 1) stream morphology and physical habitat responses to land-use change are lagged in time, introducing considerable temporal noise in synoptic datasets; 2) lagged geomorphic responses accentuate and complicate the influence of drainage-basin area on habitat characteristics; 3) spatial variation of geology and physiography is large relative to the magnitude of land-use stress in this rural landscape, resulting in considerable spatial noise; 4) the karst landscape of much of the region tends to produce a bimodal sediment load and flashy hydrology; clay and silt are flushed from these streams whereas chert gravel moves slowly, resulting in land-use induced aggradation by coarse sediment rather than fine; 5) fish species distribution and abundance appear to be affected by drainage network structure as well as historical artifacts.