Browsing by Subject "Sediment"

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    Mediated Electrochemical Reduction: A Control for Electron Transfer Reactions and Implications for Redox Cycling of Iron and Phosphorus Between Sediment and Water
    (2025-05) Maag, Natalie A.; Druschel, Gregory K.; Filippelli, Gabriel M.; Deiss, Frédérique
    Eutrophication of terrestrial lacustrine systems is an ongoing environmental issue that has grown more troublesome in recent years due to continuous historic loading of phosphorus in these systems. A major hurdle for estimating phosphorus loading in lakes arises from the difficulties in determining internal loading mechanisms that release phosphorus from iron-rich sediments during reducing conditions, driven by stable hydrodynamic conditions that occur typically during colder months. Using mediated electrochemical reduction techniques to drive reduction in experimental sediment systems representing those near the sediment water interface, we found that both iron and phosphorus are released from sediments, however subsequent aqueous geochemical analysis of the system does not account for all the iron and phosphorus in the initial sediment sample. With natural sediment samples obtained from Missisquoi Bay, Lake Champlain, Vermont, iron and phosphorus released from sediments after reduction continued to increase with increasing sediment samples. Further experimentation with phosphate-sorbed ferrihydrite and goethite samples resulted in aqueous solution saturation of these components, and loss of these components in the aqueous phase likely as a result of reprecipitation of iron-phosphate mineral precipitation. Increasing phosphate in solution also significantly decreased the reduction extents and rates of phosphate-sorbed ferrihydrite minerals, indicating that phosphate sorption may create a shielding effect of these minerals and prevent electron transfer at surface sites.
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    Midcontinental Hydroclimate Variability from a 1,500-yr Wisconsin Lake Sediment Record
    (2023-12) Nealy, Cameron Alexander; Bird, Braxton; Gilhooly, William, III; Licht, Kathy
    Lacustrine sediment archives preserve continuous records of changes in basin- to regional-scale processes that reflect broader variability in climatic conditions. Here, we present a 1,500-yr sediment record of inferred effective moisture (P/E) that spans the Current Warm Period (CWP; last 150 years), Medieval Climate Anomaly (MCA; ca. 950–1250 CE), and Little Ice Age (LIA; ca. 1300–1800 CE) from glacially-formed Pope Lake in central Wisconsin. A suite of sediment proxies constrained by 14C and 210Pb ages was developed at decadal resolution to investigate Common Era changes in Upper Midwest effective moisture in response to temperature and synoptic scale atmospheric variability, such as the Pacific North American (PNA) pattern. Lake water isotopes reconstructed with authigenic carbonate oxygen isotopes (d18Ocal) from Pope Lake compare favorably with other Midwestern closed-basin lakes, indicating that evaporation was a significant control on the isotopic composition of lake water. Relatively lower d18Ocal values during the MCA suggest that the moisture availability was greater during the MCA than LIA, despite increased air temperatures. This is supported by low carbon/nitrogen (C/N) ratios and low terrestrial lithic contributions that reflect increased lake levels during the MCA. Reversals of these trends during the cooler LIA were observed. Comparisons of the Pope Lake record to synoptic scale forcings suggest that shifts in regional P/E were consistent with high amplitude PNA variability that likely affected the source and seasonality of precipitation. The general warm/wet and cool/dry relationship noted during the MCA and LIA underscores how global temperature anomalies may alter the balance of effective moisture in the Upper Midwest in relatively short succession. The Pope Lake sediment record presented here is an important step in establishing hydroclimatic history that may inform expectations of future climate for a region sparsely populated with similar high resolution late Holocene records.