Browsing by Subject "sulfate"

Now showing 1 - 4 of 4
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    The Effect of Atmospheric Sulfate Deposition on Mercury Biogeochemistry in an Experimental Peatland: Impacts, Recovery, and Natural Variability
    (2014-07) Coleman Wasik, Jill
    Elevated mercury deposition resulting from human activities has caused wide-spread mercury contamination of aquatic systems around the world. Peatlands are generally considered to be sinks for mercury deposited to the landscape, but also act as biogeochemical reactors wherein inorganic mercury is transformed into bioaccumulative, organic methylmercury (MeHg). Recent, short-term investigations have demonstrated that sulfate deposition alone can increase MeHg production in, and flux from, peatlands through the stimulation of sulfate-reducing bacteria, a group of known mercury methylators. However, over longer periods of time the interaction between the biogeochemical cycles of mercury and sulfur is complicated by variability in climate, hydrology, and sulfur and mercury deposition rates. These complexities were addressed by experimentally altering sulfate-loading to a 2.5-ha peatland in northern Minnesota over eight years. The peatland was initially divided into control and experimental treatments and sulfate was added to the latter three times each field season in simulated rainfall events. Porewaters were sampled before and after each sulfate addition and peat samples were collected five times from sites located within the raised central bog and along the peatland margins. The lagg margin is generally considered to be the primary site of mercury methylation in peatlands. However, sulfate addition caused more pronounced and persistent increases in MeHg in the central bog sites, relative to the margin sites, demonstrating that sulfate delivery to the central bog can greatly expand the areal extent of mercury methylation in peatlands. MeHg production also responded to sulfate release following severe summer drought. The increase was much higher in experimental-treatment sites than in control sites suggesting that the experimental treatment was "primed" to quickly respond to new sulfate inputs. In early 2006 sulfate addition was halted to the upgradient one-third of the original experimental treatment in order to monitor how MeHg production changed as sulfate deposition declined. Although drought appeared to slow the recovery process by increasing sulfate availability and mobilizing MeHg, three years after sulfate additions ceased MeHg in the recovery treatment was significantly lower than in the experimental treatment. This indicates that MeHg production in peatlands formerly affected by elevated sulfate deposition may return to background conditions and highlights the potential benefits that further controls on atmospheric sulfur emissions may have on MeHg production in peatlands and consequent mercury burdens in aquatic foodwebs. The long-term nature of this study allowed for an in-depth exploration of the effects that hydrologic flucutations on mercury cycling in peatlands and calls attention to the potential negative consequences that changing precipitation patterns and evapotranspirative demands may have on MeHg production in these systems.
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    The Effect of Sulfate Contamination of Water on Wild Rice Nutrient Composition
    (2023-02) Johnson, Katelyn
    Sulfate contamination of waters where wild rice grows threatens its survival. Toxic levels of sulfate affect growth and development, which leads to reductions of natural stands. Research shows that when sulfate is reduced to sulfide, it interacts with iron in sediment to precipitate iron-sulfide. Iron-sulfide plaques accumulate on wild rice roots, which inhibits nutrient uptake from soil. This study examined changes in wild rice nutrient composition by analyzing rice samples grown in low-sulfate and high-sulfate waters under natural and experimental conditions. Samples collected from experimental mesocosms included “low-sulfate’ controls (10 mg/L SO4) and “high-sulfate” amended (300 mg/L SO4). Natural site samples collected from two bodies of water surrounding the Great Lakes Region; Big Rice Lake (“low-sulfate” non-detect) and Sand River (“high-sulfate” > 46.2 mg/L SO4), respectively. We measured antioxidant capacity, plant secondary metabolites, total starch, and mineral content, including mercury, of eight wild rice samples. Wild rice exposed to sulfate in natural and controlled environments had decreased seed sizes and weight. Reductions in seed size appeared due to a reduced amount of starch, as starch content and seed size were highly correlated. Certain trace minerals were reduced to a greater degree than the reduction in seed size, particularly iron, copper, and zinc. Since iron and copper are both required for starch synthesis, and copper deficiency increases synthesis of starch-degrading enzymes, deficiencies of copper and iron may be responsible for the reduced starch content of the wild rice seeds, thus producing a smaller seed size.
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    Evolving reactivity and products of natural iron-bearing minerals toward sulfide
    (2019-12) Daire, Jacob
    Iron minerals play dynamic roles in the sulfur cycle in natural environments and engineered systems. Although pure or synthesized iron minerals are widely studied for their importance in the sulfur cycle, heterogeneous iron-bearing materials are important since they are found naturally and may be economically feasible for engineered sulfur treatment. In this study, reaction capacities, products, and kinetics of two natural iron-bearing minerals derived from taconite towards aqueous sulfide were studied using batch and column reactors. Siderite (SR)- and iron oxide (IO)-rich natural minerals were selected based on distinction in iron mineralogical characteristics and quantity. The siderite rich SR reacted with more sulfide per gram (FeR), over the iron oxide rich IO. SR produced more solid phase sulfur, liberated by 9 N HCl (AVS) and chromic acid, where IO produced more elemental sulfur and thiosulfate. Sulfate as an oxidation product was minimal for both materials in batch and column reactors. Reaction kinetics were dependent upon the molar ratio FeR/HSinitial. Generally, initial reaction rate increased with increasing FeR/HSinitial, or as iron becomes the dominant reactant. SR maintained an appreciable reaction rate with each sequential spike and differing particle sizes, reaction rate constant (k) falling only slightly below the expected relationship. IO exhibited a high initial reaction rate, but its reaction rate constant decreased substantially with sequential sulfide spikes and varied greatly with larger particle sizes. In continuous flow column reactors, both materials FeR and AVS increased over batch reactor values. A reactive-transport model was developed using batch reactor kinetic results to establish reaction rate, k, dependence on FeR/HSinitial, and was used to describe sulfide evolution through a column. In summary, the selected materials generally reacted predictably with sulfide with respect to their iron mineralogy and experienced predictable sulfur reaction kinetics and capacities across different loading scenarios. These results represent an important step toward elucidating the reactivity of heterogeneous iron-bearing materials at the interfacial processes with the cycles of Fe and S and sulfur treatment systems.
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    Minnesota Pollution Control Agency Wild Rice Sulfate Standard Mesocosm Study: Water, Sediment, and Porewater "Synoptic" Sampling 2013 and 2015
    (2017-05-30) Myrbo, Amy; amyrbo@umn.edu; Myrbo, Amy
    This dataset represents opportunistic, "synoptic" sampling of 30 experimental mesocosms for chemical parameters. The mesocosm experiments were undertaken by Dr. John Pastor (UMN-Duluth) and the Minnesota Pollution Control Agency (MPCA) to improve the understanding of why wild rice (Zizania palustris, manoomin, psin) is observed to thrive only in waters with low sulfate (SO4), and to contribute to evaluation of Minnesota Rules 7050.0224, promulgated in 1973, which seeks to limit the exposure of wild rice to sulfate concentrations exceeding 10 mg/L.The dataset is now released as manuscripts using it are being published.