Browsing by Subject "Biogeochemistry"

Now showing 1 - 7 of 7
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    Agricultural Wetland Restoration: The Role of Sediment Removal, Hydroperiod and Time on Restoration Outcomes
    (2021-06) Winikoff, Sarah
    Restoring agricultural wetlands to remediate nutrient runoff, decrease flood risk, and improve wildlife habitat are areas of growing interest. One restoration strategy that may improve species diversity, enhance water retention, and decrease nutrient availability is the removal of accumulated eroded sediment from agricultural wetlands prior to restoration. In this work, we the measured physical and chemical characteristics of soils, characterized plant communities, and examined water column nutrient availability and denitrification potential in 54 restored agricultural wetlands in west central Minnesota. In half of the wetlands hydrologic function was restored by removing and plugging drainage tile and ditches, while hydrology was restored in the remaining basins following sediment removal (Excavation treatment), increasing basin depth by an average 30 cm. Excavation primarily influenced the plant community, by delaying the establishment of two invasive emergent macrophytes, hybrid cattail (Typha x glauca) and reed canary grass (Phalaris arundinacea), but the affect only lasted for 6 years. Contrary to expectations, soil properties, water column dissolved nutrients, and denitrification potential were all primarily influenced by hydroperiod – the number of consecutive days with standing water. Wetlands with longer hydroperiods had less bioavailable P in soils, lower dissolved N and P concentrations, and lower denitrification potential. We also found evidence that vegetation likely plays an important role in dissolved nutrient dynamics over time. Our results suggest that excavation may be an important tool in wetland restoration but its influence was lost as wetlands aged in the absence of invasive species management. Moreover, nitrogen and phosphorus dynamics were almost universally controlled by hydroperiod, with tradeoffs between nitrogen removal and phosphorus remineralization.
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    Biogeochemistry of southwestern Lake Superior and watershed, 2017-2021
    (2023-09-28) Sterner, Robert W.; Lafrancois, Brenda M; stern007@d.umn.edu; Sterner, Robert W.; Large Lakes Observatory, University of Minnesota
    Between 2017 and 2021, 1368 water samples were collected from Lake Superior and its watershed in the region generally between Duluth-Superior and Ashland, WI. Parameters include forms of carbon, nitrogen, and phosphorus, along with total suspended solids, chlorophyll, and phycocyanin.
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    Effect of topography and glaciation history on the movement of carbon and nitrogen within arctic hillsides.
    (2010-04) Whittinghill, Kyle A.
    The transport of dissolved organic matter (DOM) down hillslopes to aquatic ecosystems has important implications for both terrestrial and aquatic primary productivity. DOM is an important energy and nutrient source for both terrestrial and aquatic microbes. Within watersheds, physical, chemical, and biological processes transform DOM, but it not well known how landscape heterogeneity may affect these processes in arctic watersheds. In the northern foothills of the Brooks Range, expansion and contraction of mountain glaciers over the last several ice ages have created a mosaic of landscape ages with similar climate and vegetation. My research indicates that younger landscapes (<50,000yrs) have significantly lower pH, 10x higher exchangeable base cation concentrations, and significantly lower rates of DOM production and microbial respiration than older landscapes, which could significantly affect fluxes of carbon and nutrients across the landscape. At the watershed scale, I examined patterns in soil and stream water concentrations of DOM within hillslopes across the chronosequence. I found that while concentrations of dissolved organic carbon decreased significantly moving downslope from the hilltop to the stream; dissolved organic nitrogen concentrations remain similar within the hillslope, but are significantly different among landscape ages. I also used a variety of indices to examine spatial patterns in the biodegradability of DOM within hillslopes and among landscape ages in northern Alaska. My results suggest the low biodegradability of DOM found in streams and rivers in the region is not due to microbial processing of labile DOM in terrestrial ecosystems, but rather to production of recalcitrant DOM throughout the landscape.
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    Impact Of Increased Temperature And Atmospheric Carbon Dioxide On Mercury And Sulfur Speciation In Peatland Soils
    (2018-08) Krupp, Anna Lucia
    Environmental mercury (Hg) pollution exists as a global public health issue without any localized borders. Volatile Hg emissions travel freely throughout the atmosphere, allowing anthropogenic point-source industrial emissions to have truly global impact. Recent research demonstrates that climate change may further impact the extent of environmental mercury pollution through increased production of monomethylmercury, more commonly known as methylmercury (MeHg), by various microorganisms within the soil, including sulfate-reducing bacteria, iron-reducing bacteria and methanogens. Continued research on the subject is warranted to fully understand the impacts of climate change on the environmental biogeochemical cycling of Hg and MeHg on various natural systems. Increasing global temperatures and levels of atmospheric CO2 could significantly increase the net conversion of Hg to MeHg by sulfate-reducing and iron-reducing bacteria in systems particularily vulnerable to climate change such as ombrotrophic peatbogs, leading to an increased size in the net MeHg pool overall. The Supplementary Files attached to this thesis document include the following files: raw data (SPRUCE_2012_2014_2015_2016_Peat_Final_Data.xlsx), untransformed multiple linear regression values (Regression_Non_Transformed.xlsx), log transformed multiple linear regression values (Regression_Log_Transformed.xlsx), maximum value calculations (Max_Calculations.xlsx), and fitted XANES data for 2012 (SPRUCE-2012-fit7-tidy.xlsx), 2015 (SPRUCE-2015-fit4-tidy.xlsx), and 2016 (SPRUCE-2016-fit4-tidy.xlsx).
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    Impacts of earthworm bioturbation on elemental cycles in soils: An application of a geochemical mass balance to an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota.
    (2013-06) Resner, Kathryn "Kit" Elizabeth
    Earthworms are arguably the best known soil bioturbator, yet their impacts on soil biogeochemistry are difficult to quantify as a function of their roles in physically mixing soils. In glaciated regions of North America, northern hardwood forests have evolved without native earthworms since the last glacial retreat. However, earthworms have invaded northern hardwood forests owing to agricultural expansion, fishing, recreational, and logging activities. Earthworm consumption of the organic horizon in Minnesota hardwood forests has resulted in dramatically changing forest floor ecology and soil morphology, yet their impacts on soil biogeochemistry remain largely unknown. An earthworm invasion chronosequence near Leech Lake in Northern Minnesota provides an ideal outdoor laboratory to quantify the interactions between biogeochemical and physical processes associated with different earthworm species and biomasses. Across the earthworm invasion transect, the A horizon elemental chemistry profiles show that earthworms have vertically relocated minerals, which is consistent with 210-Pb activity profiles. While soil elemental depth profiles confirm increased mixing with earthworm invasion, the depth profiles cannot be solely explained by mixing. I used a geochemical mass balance model to examine soils' biogeochemical responses to invasive earthworms. Fractional and absolute mass losses/gains of biologically important elements such as Ca, P, K, Fe, and Si, relative to the parent material, are substantially altered by invasive earthworm species. The arrival of A-horizon-mixing, endogeic earthworms most dramatically reduces the level of the elemental enrichments in the A horizons. The declined elemental enrichments are likely derived from the consumption of particulate organic matter by endogeic species, which leads to the mineralization and leaching of Ca, P, K. The dramatic losses of the enrichments also suggest that the newly mineralized nutrients are in excess of the nutrient demand from understory plants. Our results indicate the significant and potentially negative impacts of invasive earthworms on the soil nutrient cycling and consequently the sustainability of the hardwood forests in the Great Lakes Region.
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    Publications from LLO Faculty and Staff, 2016
    (2016) University of Minnesota Duluth. Large Lakes Observatory
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    Sources, biogeochemical cycling, and fate of organic matter in Lake Superior: an investigation using natural abundance radiocarbon and stable isotopes
    (2012-01) Zigah, Prosper Kojo
    The natural abundance radiocarbon and stable isotopic distributions of bulk dissolved organic carbon (DOC), particulate organic carbon (POC), dissolved inorganic carbon (DIC), zooplankton, size-fractionated organic matter, and biochemical compound classes were used to investigate the sources, biogeochemical cycling, and fate of organic matter in the water column of Lake Superior. DIC pool appears to reset rapidly, showing radiocarbon values similar to atmospheric values from approximately 3 years previous to sampling. DIC concentrations and isotopic compositions were mostly homogeneous across the entire lake. POC was generally more depleted in stable carbon isotopic values than concurrent DOC. POC was also consistently depleted in radiocarbon (thus, older) relative to DOC and DIC. Radiocarbon ages of POC was spatially heterogeneous (range, modern to 2,840 year BP), and appear to be related to total water depth, exhibiting more older and more variable ages in the deepest basins of the lake. The ages and reactivity of bulk DOC did not change radically across the lake. DOC pool appears to be semi-reactive, recycling over up to 60 years in the entire water column. The radiocarbon signatures of the various DOC size fractions show that they recycle on similar time scales, with consistently modern (post 1950) radiocarbon values. Radiocarbon and Nuclear Magnetic Resonance (NMR) data show most of the high molecular weight dissolved organic matter (HMW DOM) originates from contemporary origin and was dominated by carbohydrates, aliphatic compounds, and acetate, with little aromatic compounds. Total hydrolyzable free carbohydrates and amino acids within HMW DOM exhibited modern radiocarbon signatures and recycled rapidly in the lake. In contrast, extractable lipid was pre-aged (20 to 2,320 years BP) due to older sources and/or general long term persistence in the lake. Coupled radiocarbon and stable carbon isotopic values indicate multiple sources, and variable formation pathways for the acid insoluble organic fraction within HMW DOM in the lake. Radiocarbon and stable isotopic values show zooplankton in Lake Superior selectively feed on within-lake produced organic matter even though other organic carbon sources represented a considerable portion of the available food resource.