Impact of Man-Made Reservoirs on Stream Water Quality on the Southern Cumberland Plateau of Tennessee: A Preliminary Report

The study area is located on the southern Cumberland Plateau in the vicinity of Sewanee, Tennessee. Here several small lakes were constructed by the establishment of earthen dams across first order drainages that are part of an overall dendritic drainage network developed on flat-lying, Pennsylvanian sandstones, shales, and conglomerates rich in iron and manganese oxides. All lakes in the area are characterized by elevated levels of iron and manganese in their deeper portions. These metal-rich waters seep through the earthen dams and deposit iron and manganese as “yellow boy” on streambeds below the dams. Water samples were collected from streams at 100 foot intervals below the dams of six lakes. These were analyzed (ICP-MS) for over 60 inorganic elements, including iron and manganese. Analyses show that stream iron and manganese concentrations are highest near the dams (> 8000 ppb and > 1300 ppb, respectively) and drop below 200 ppb iron and 100 ppb manganese at 400 feet downstream of the dams. At 3000 feet below the dams the concentrations of iron and manganese are below 10 ppb. Our study further demonstrates that the presence of visible “yellow boy” on stream floors is an indicator of elevated iron and manganese concentrations in the overlying stream waters. These findings represent the first extensive study of metal concentrations in stream waters below reservoirs on the Cumberland Plateau of Tennessee. The results may have an impact on further construction of lakes atop the Cumberland Plateau of Tennessee since the Tennessee Department of Environment and Conservation placed a moratorium on such lake construction due to concerns over elevated metal concentrations in streams below dams.