Concentration-discharge regression parameters in watersheds of varying lithology subjected to surface coal mining and reclamation

ABSTRACT:

Evaluations of the impacts of mining and reclamation require knowledge of changing hydrologic conditions and of changing sources and rates of release of chemicals into stream waters. Not much is known regarding the watershed-scale effects of mining and reclaiming watersheds on relations between surface-water chemical concentrations (C) and instantaneous discharge (Q) for different geological settings. These impacts were evaluated on three geologically dissimilar, small experimental watersheds subjected to surface mining for coal (Co6, Mo9, and J11). Comparisons were made across watersheds during similar types of land disturbances during natural/undisturbed conditions (Phase 1), land disturbances caused by mining and reclamation activities (subphases of Phase 2), incomplete reclamation (subphases of Phase 3), and the final condition of the watersheds (Phase 3F). Regression analysis used a total of 5,047 laboratory analyses of 36 constituents. Of 429 regressions, 153 (36%) were statistically significant. More statistically significant regressions using a power equation were found during Phases 1 and 3F at the three sites - relatively stable watershed periods. The stability in log concentration versus log instantaneous discharge relations is quickly achieved for some constituents, mostly for major ions. Constituents for which significant regressions were found across all three watersheds during different phases of watershed disturbance were identified. Sign of the chemical concentrations - instantaneous discharge (C-Q) regression slope parameter (exponent of the power equation) was similar across the three geologically dissimilar watersheds for different phases. This study contains tables that document expected chemical concentrations - instantaneous discharge (C-Q) relations and changes in parameters due to mining coal seams and reclamation activities for 36 chemical constituents, using two mining methods, three reclamation practices, and three distinct geologic settings. The tables also provide guidance for simplified field sampling of streams for correlated and uncorrelated constituents.