Drainage from abandoned underground coal mines negatively impacts many miles of stream habitat throughout the Appalachian region. The drainage is commonly called acid mine drainage (AMD) due to its low pH; however, not all mine drainage is acidic. The quantity and quality of the water discharged from a coal mine depend upon numerous variables, such as the design of the mine, chemical composition of the coal and surrounding rocks, and local climate. Coal extracted from the now-abandoned Cherry Valley Coal Mine near Leetonia, Ohio, was reached by a slope entry such that the mine is not entirely up-dip, and a significant area is flooded. Recharge water that enters the unsaturated area of the mine mobilizes soluble iron-sulfate salts as it flows down-dip and adds pyrite oxidation products to the mine pool. The bedrock overburden is covered by calcareous glacial till that imparts alkalinity to the shallow groundwater, buffers the acidity, and keeps the pH inside the mine circumneutral. Maintaining a circumneutral pH reduces pyrite oxidation by decreasing the solubility of ferric iron, the primary oxidizing agent of pyrite at low pH, which reduces the positive feedback mechanism that drives pH down and concentration of oxidation products up. Shallow groundwater is brought to the mine via subsidence fractures, which facilitate a rapid increase in discharge from the mine (and dilution of oxidation products) in response to surface runoff events. The loadings of all dissolved ions, except iron, are controlled by the changes in discharge rather than the changes in concentration.
Mid- to late-Holocene Indian Winter Monsoon Variability from a Terrestrial Record in Eastern and Southeastern Coastal Environments of Sri Lanka07/01/2013
The southeastern coastal plain of Sri Lanka contains Holocene sediment archives representing the winter monsoon variability because this region is protected from both summer monsoon and cyclonic rainfall. Chemical, biological, mineralogical, and physical climate proxies were studied in sediment cores extracted from three different coastal estuaries and lagoons situated on the southeastern coast to derive winter monsoon variability. These cores displayed minimum influence of sea level-related changes in sediments. Clay normalized proxy records suggest intervals of aridity from >7300 to ~6750, semi-aridity from ~6250 to 4600 yr BP, and aridity from ~4000 to 3000 and ~1100 toBP, with a short wet interval from ~6500 to 6250 cal. yr BP, and a wet interval from ~3000 to 1500 yr BP. Our results match the timing of previously published climate events for Holocene variations in the Indian summer monsoon. Wavelet analysis of the detrended climate proxy records identify significant periodicities at: ~20 ~28–32, ~64, ~100, ~128, ~192, ~256 yr in our data. Most of these periodicities are consistent with known solar irradiance cycles, which drive the decadal- to centennial-scale variability of the summer monsoon. Our multiproxy record for mid- to late-Holocene climate in southeastern Sri Lanka documents that Indian winter monsoon variability is statistically similar to Indian summer monsoon variability, suggesting similar forcing mechanisms.