COMPARATIVE LIMNOLOGIC EVOLUTION OF LEE CREEK RESERVOIR AND LAKE SHEPHERD SPRINGS, CRAWFORD COUNTY, NW ARKANSAS

Analyses of time-varying trends in water quality parameters combined with geospatial data provided insight into the limnologic evolution and watershed-scale processes driving limnetic succession of two man-made reservoirs in northwest Arkansas. Lee Creek Reservoir was constructed in 1992 and occupies a relatively large watershed (1,163 km²) with significant human land use activities (agriculture = 15%). Lake Shepherd Springs was constructed in 1956 in a much smaller watershed (173 km²) that remains 90% forested with minor, dispersed human land use (agriculture = 8%). Results of this study indicated these lakes were evolving along different limnologic trajectories driven by variations in watershed physiography, reservoir morphometry, watershed land use and land cover, and human activities within the watershed. The integrated impact of watershed-scale processes was manifest as an order of magnitude increase in observed oxygen depletion rate within the summer hypolimnion of Lee Creek Reservoir relative to Lake Shepherd Springs (0.0054 mg/L vs. 0.00046 mg/L). The observed rate of oxygen depletion in Lee Creek Reservoir resulted in hypoliminion anoxia in mid-June whereas the hypolimnion of Lake Shepherd Springs became anoxic in late August. Thus, Lee Creek Reservoir appeared to be advancing more rapidly toward eutrophication than Lake Shepherd Springs, despite the fact that it was only 1/5 as old. This study illustrated the value of integrating geospatial and archival water quality data to provide insight into the dynamic aspects of watershed processes and their impacts of the limnologic evolution of surface water reservoirs.