Quantifying Human Impacts on Trace Metal and Sediment Cycles: Evidence from Oil and Gas, Coal Mining, and Land Development in the U.S. and China

Human land use changes (i.e.. agricultural clearance and coal mining) have mobilized substantial volumes of sediments. At the same time, human activity, such as petroleum extraction, loaded sediments with metal contaminants. Land use changes alter geomorphic cycles, spreading localized, concentrated contamination to broader areas. Spatial redistribution during sediment flux combined with multiple eras of metal contamination make estimating the spread of contaminated sediments even more complex. This dissertation examines the impacts of coal mining, petroleum extraction, and agricultural clearance on basin sediment dynamics and trace metal cycles. Here, I document the impact of human activities on geochemical and geomorphological cycles through the: 1) Development of Ca/Mg and Ca/Sr as a chemical framework to differentiate among conventional brines, unconventional brines, and non-impacted waters in oil and gas extraction landscapes; 2) Combination of soil erosion modeling with sediment dynamics histories reconstructed from previously collected lake cores to constrain estimates of floodplain accumulation rates over 2,000 years of land use change in Yunnan, China; and 3) Reconstruction of floodplain accumulation downstream of historical strip-mining in southwest Pennsylvania. Long- and short-term land use change impacts on trace metal and sediment cycles were revealed: 1) Ca/Mg and Ca/Sr ratios allow distinction among source contributions of conventional brines, unconventional brines, and non-impacted waters, providing a relatively simple method to evaluate water chemistries in areas with both conventional oil/gas and unconventional shale gas extraction; 2) Soil erosion model simulations and lake sediment accumulation rates suggest a lag between erosion and deposition in the lake. In Xingyun watershed, China, an agricultural clearance threshold was identified as estimates of soil erosion change rapidly when ~32% of the landscape is cleared for agriculture; and 3) During the strip-mining period in southwestern Pennsylvania, strip-mined sediments were deposited in smaller, headwater floodplains. The majority of strip-mined sediments are still stored as colluvium or alluvium in the smaller watersheds. This dissertation illustrates that legacy human activities impact modern basin sediment dynamics and the redistribution of legacy metal contamination. Ultimately, results from this dissertation provide a framework for improving current watershed management practices