Geology
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Item Developing Sensor Proxies for “Chemical Cocktails” of Trace Metals in Urban Streams(MDPI, 2020-10-14) Morel, Carol J.; Kaushal, Sujay S.; Tan, Maggie L.; Belt, Kenneth T.Understanding transport mechanisms and temporal patterns in the context of metal concentrations in urban streams is important for developing best management practices and restoration strategies to improve water quality. In some cases, in-situ sensors can be used to estimate unknown concentrations of trace metals or to interpolate between sampling events. Continuous sensor data from the United States Geological Survey were analyzed to determine statistically significant relationships between lead, copper, zinc, cadmium, and mercury with turbidity, specific conductance, dissolved oxygen, and discharge for the Hickey Run, Watts Branch, and Rock Creek watersheds in the Washington, D.C. region. We observed a significant negative linear relationship between concentrations of Cu and dissolved oxygen at Rock Creek (p < 0.05). Sometimes, turbidity had significant positive linear relationships with Pb and Hg concentrations. There were negative or positive linear relationships between Pb, Cd, Zn, and Hg and specific conductance. There also appeared to be relationships between watershed areal fluxes of Pb, Cu, Zn, and Cd in streams with turbidity. Watershed monitoring approaches using continuous sensor data have the potential to characterize the frequency, magnitude, and composition of pulses in concentrations and loads of trace metals, which could improve the management and restoration of urban streams.Item An empirical re-evaluation of the boron isotope/pH proxy in marine carbonates(2009) Klochko, Kateryna; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The boron isotopic composition measured in marine carbonates is considered to be a tracer of seawater pH. However, an accurate application of this proxy has been hampered by our lack of intimate understanding of chemical kinetics and thermodynamic isotope exchange between the two dominant boron-bearing species in seawater: boric acid B(OH)3o and borate ions B(OH)4-, as well as their subsequent partitioning into a carbonate lattice. In this dissertation I have taken on a task of a systematic empirical re-evaluation of the fundamental parameters and assumptions on which the boron isotope paleo-pH proxy is based. As a result of this research strikingly different values of the boron isotope exchange constant in solution (Klochko et al., 2006) and boron speciation and partitioning in carbonates (Klochko et al., 2009) were determined, suggesting that the most parameters and assumptions that were believed to be previously constrained and have been widely applied to the 11B-pH reconstructions were incorrect. Recognizing that both biological and inorganic processes may potentially affect boron speciation and isotopic composition in carbonates, to isolate purely inorganic effects on the boron isotope co-precipitation with carbonates, we have designed a series of pH-controlled 11B calibration experiments of inorganic calcite and inorganic aragonite. Results to date reveal that precipitates from our experiments at pH = 8.7 fall exactly along the borate ion 11B curve predicted by our empirically determined boron isotope fractionation factor (Byrne et al., 2005; Klochko et al., 2006). Extending these experiments to wider range of pH conditions will provide the necessary inorganic baseline for paleo-studies of inorganic carbonate and future investigations of the purely biological effects on the boron isotope distributions in carbonates.