Browsing by Subject "Mitigation"

Now showing 1 - 4 of 4
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    Assessing Agricultural Nitrous Oxide Emissions and Hot Moments Using Mesocosm Simulations
    (2021-02) Miller, Lee
    Nitrous oxide (N2O) is a major greenhouse gas and the leading stratospheric ozone depleting substance emitted today. Effective mitigation strategies from agricultural soils, the largest anthropogenic source of N2O, have remained elusive due to the occurrence of difficult to predict “hot moments,” or brief periods that contribute disproportionately to N2O budgets. Future precipitation patterns may further complicate mitigation efforts by causing more favorable soil conditions that drive N2O emissions. The objectives of this thesis, therefore, were to: 1) Assess the sensitivity of N2O emissions to changes in precipitation; 2) Devise an approach to objectively identify hot moments; and 3) Identify the conditions that drive these hot moments. Six growing season simulations with nearly continuous N2O measurements from an indoor mesocosm facility were used to address each of these objectives.Four seasons comparing historical normal (1984-2014) versus end-of-century (2071-2099) precipitation patterns demonstrated that, for non-limiting soil nitrogen, the greatest N2O emissions occurred when soil water-filled pore space (WFPS) was between 40 and 80% and that cumulative emissions increased with the number of days above ~60% WFPS. Consequently, any future changes in precipitation that contribute to these conditions will likely increase N2O emissions. An assessment of 1350 rain events revealed that N2O emissions consistently increased within 24 hours of rainfall and when soil moisture was near ~60% WFPS and NH4+ was greater than 10 mg N kg-1 soil. However, emissions were suppressed when WFPS was ~60% and soil NH4+ was below 5 mg N kg-1 soil, demonstrating that soil NH4+ availability is an important determinant of the N2O emission response to rain. Finally, a new approach to categorize hot moments from background N2O emissions identified greater soil nitrate (NO3-), air temperature, and 10 cm WFPS among hot moments. Further, short-term pulses (up to 38 hours) of hot moments were sustained when nitrate (NO3-) was greater than 50 mg N kg-1 soil and WFPS was above 50%, and were controlled by short-term changes in WFPS and air temperature. These findings have important implications for the development of N2O emission models, agricultural management and mitigation strategies, and demonstrate the efficacy of conducting mesocosm experiments under controlled conditions.
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    Effects of Aquaculture on Mine Pit Lakes near Chisolm, MN: Restoration of Twin City-South pit lake by fallowing and status of Fraser pit lake
    (University of Minnesota Duluth, 1995) Axler, Richard P; Yokom, Shane; Tikkanen, Craig A; Henneck, Jerald; McDonald, Michael E
    Net-pen salmonid aquaculture was carried out from 1988 to 1993 in the Twin City-South mine pit lake on the Mesabi Iron Range in northeastern Minnesota. A water quality controversy enveloped the aquaculture operation from its inception in 1988. In 1992 the Minnesota Pollution Control Agency mandated that all intensive aquaculture operations in the Twin City - South mine pit lake be terminated by July 1993 and that restoration to baseline (i.e. preaquaculture) conditions be demonstrated within three years. This "fallowing" has led to a rapid recovery to near baseline water quality conditions and an oligomesotrophic, i.e. unproductive, status. Water column improvement in regard to phosphorus and hypolimnetic oxygen concentrations has been particularly rapid. Although baseline conditions were not well defined for TC-S, the P budget for the lake in September and November 1994 was typical of reference pit lakes in the area. Oxygen concentrations in near-bottom water remained above 5 mg02/L in November 1994 even without artificial mixing or aeration during the 1994 growing season. Algal growth was low in 1993, as expected due to artificial mixing, and remained low in 1994 without any artificial mixing. Ammonium has been naturally converted to nitrate which is decreasing faster than expected and at a rate similar to its increase during intensive aquaculture. More rapid reductions in water column phosphorus and nitrogen might have been accomplished during the first summer by allowing the lower hypolimnion to become anoxic in order to promote denitrification and minimize sediment resuspension. The natural burial of sedimented aquaculture wastes due to high ambient rates of erosion of inorganic sediment from the basin walls has effectively minimized sediment nutrient transport to the overlying water column. Fallowing for several years appears to be an effective method for lake restoration of these pit lakes. Our data, and our analysis of the NPDES monitoring data, has shown no change in the water quality of Chisholm's drinking water source, the Fraser pit lake, attributable to aquaculture impacts. This, and no apparent change in the water quality of two nearby pit lakes, Grant and Ironworld in recent years, suggests little or no significant off-site migration of aquaculturally impacted water.
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    Land-use transport models for climate change mitigation and adaptation planning
    (Journal of Transport and Land Use, 2018) Ford, Alistair; Dawson, Richard; Blythe, Phil; Barr, Stuart
    The adoption of the Paris Agreement has committed the world to limiting anthropogenic climate change to 2°C above preindustrial levels, adapting to climate risks, and fostering climate resilience. Given the high proportion of global emissions released by cities and the concentration of people living in urban areas, this will require an unprecedented reduction in greenhouse gas emissions and transformation of the built environment on a yet unparalleled timescale. This poses substantial challenges for urban land-use and transport planning and for the use of land-use transport models (LUTM), which have historically been developed to test incremental changes rather than the rapid transformations implied by the Paris Agreement. This paper sets out the need for a new generation of tools to support the planning of a transition toward a low-carbon and resilient future, arguing that land-use and transport modeling tools are crucial to support this process. Recent developments in urban integrated assessment that link models of land-use and transport with other environmental models of greenhouse gas emissions and climate hazards show promise as platforms to assess the potential of urban policies in achieving the goals set out in the Paris Agreement. The paper concludes by defining challenges for the LUTM community if it is to achieve these goals. Crucial will be the adoption of new modeling approaches to better represent rapid social and technological change and to concurrently assess the resilience and sustainability implications of different land-use and transport policies. Simple models to explore multiple scenarios of change must be integrated with more sophisticated models for detailed design. Collaborative approaches will be necessary to allow multiple stakeholders to use these tools to explore urban futures and design radical urban transitions across multiple and interdependent urban sectors.
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    Limnological Re-Sampling of Chisolm Area Mine Pit Lakes with Reference to Former Aquaculture Impacts
    (University of Minnesota Duluth, 2000) Axler, Richard P; Henneck, Jerald
    Limnological surveys were conducted on two mine pit lakes (Twin City-South and Sherman) used for intensive netpen salmonid aquaculture over the period 1988-1995 and an adjacent pit lake (Fraser) used for drinking water by Chisholm, Minnesota. A water quality controversy had enveloped the aquaculture operation from its inception in 1988 to its bankruptcy in 1995. All intensive aquaculture operations in the Twin City-South pitlake were terminated in mid-1993 as mandated by the Minnesota Pollution Control Agency (MPCA) in order to determine if water quality could be returned to baseline values within three years (a condition of continued operation in the Sherman pit lake). The MPCA mandated that restoration to baseline (i.e. pre-aquaculture) conditions be demonstrated within three years. This "fallowing" led to a rapid recovery to near baseline water quality conditions and an oligomesotrophic, i.e. unproductive, status. Algal growth was low in 1993, due to light - limitation from artificial mixing, but remained low in 1994 without any management due to renewed P-limitation. Water column improvement in regard to phosphorus and hypolimnetic oxygen concentrations was particularly rapid. Although baseline conditions were not well defined for TC-S, the P budget for the lake after 18 months was typical of reference pit lakes in the area and oxygen concentrations in near-bottom water remained above 5 mg02/L without artificial mixing or aeration during the next growing season. Waste product ammonium was naturally nitrified to nitrate which decreased at a rate faster than expected, and similar to its increase during intensive aquaculture. More rapid reductions in water column phosphorus and nitrogen might have been accomplished during the first, summer by allowing the lower hypolimnion to become anoxic in order to promote denitrification and minimize sediment resuspension. Unfortunately these were precluded by the regulatory standards. The natural burial of sedimented aquaculture wastes due to high ambient rates of erosion of inorganic sediment from the basin walls effectively minimized sediment nutrient transport to the overlying water column and sediment oxygen demand.