Browsing by Subject "nutrient"

Now showing 1 - 4 of 4
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    Analysis Of Response To Climate Change In The Le Sueur River Watershed With Generated Climate Predictions
    (2020-03) Steinweg, Emily
    Climate change may have a variety of impacts on Midwest USA agriculture, including impacts to water quality, soil erosion, and nutrient loss. Existing and future climate scenarios were modeled in the Le Sueur watershed using the Soil & Water Assessment Tool (SWAT) to compare the watershed outflow and nutrient concentration outflows under those scenarios. The Le Sueur watershed, in south-central Minnesota, USA, is approximately 1,112 square miles, 87% of which is agriculture. The agriculture land is predominantly in corn and soybean rotations. Much work has been done using global climate models to predict the climate impacts from anthropogenic climate changes, resulting in predictions that the Midwest will experience increased temperatures, increased precipitation in the winter months, and decreased precipitation in the summer months. Minnesota has already documented an increase in extreme rainfall events. These events can cause flooding, damage land and property, and impact agricultural production. This analysis uses six global climate model (GCM) projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5) for the Le Sueur River watershed area. The magnitude of change of five weather inputs; maximum temperature, minimum temperature, relative humidity, solar radiation, and wind speed, was averaged over three future climate time periods (2006-2029, 2030-2059, and 2060-2099) for two emissions scenarios, RCP 4.5 and 8.5. Average changes were applied to local weather in the Weather Input for Nonpoint Data Simulations (WINDS) model to simulate local climate projections. Predictions from WINDS are used in SWAT, to investigate watershed response to climate change in the Le Sueur River watershed.
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    Dreissenid-Mediated Energy and Nutrient Cycling in Profundal Regions of the Laurentian Great Lakes
    (2023-08) Huff, Audrey
    In the Laurentian Great Lakes, invasive zebra and quagga (dreissenid) mussels have dramatically altered biotic community structure, primary productivity, and biogeochemistry since their introduction in the 1980s. Recently, quagga mussel (Dreissena rostriformis bugensis) populations have been expanding deeper into profundal regions of Lakes Michigan, Huron, and Ontario. These dense offshore populations have substantially altered offshore energy and nutrient cycling, but there are key gaps in our understanding of deep-water quagga mussel physiology and their impacts on pelagic biogeochemistry. Specifically, there is a lack of information on (1) quagga mussel tissue nutrient sequestration and regeneration rates, including variability in tissue stoichiometry (C:N:P molar ratios) and its influence on mussel excretion rates and excretion stoichiometry, (2) quagga mussel impact on offshore sediment geochemistry, including sediment mixing rate, sediment oxygen penetration, and dissolved nutrient dynamics at the sediment-water interface, and (3) quagga mussel population dynamics, including size distribution and growth rates, in deep, offshore lake regions. Presented here are the results of field (chapter 2), experimental (chapter 3), and modelling (chapter 4) studies I conducted to address these knowledge gaps about quagga mussel physiology and ecological impacts. To determine variability of quagga mussel tissue stoichiometry and its impact on mussel excretion (chapter 2), I measured mussel tissue and excretion carbon, nitrogen, and phosphorus content along depth (20 – 130m) and trophic gradients in Lakes Michigan and Huron during spring mixing and summer stratification periods of 2019. I found that mussel tissue C:N:P ratios varied substantially in Lakes Michigan and Huron, suggesting that quagga mussels have flexible internal homeostasis. I also found that tissue C:N:P stoichiometry was a significant driver of mussel excretion rates and excretion stoichiometry. When mussels had lower tissue C:P ratios than available seston, excretion C:nutrient (C:N and C:P) ratios decreased. Next, to investigate the influence of quagga mussels on offshore sediment geochemistry (chapter 3), I conducted a six-week microcosm experiment. I incubated quagga mussels, Diporeia spp. (previously the dominant Great Lakes’ macroinvertebrate), and oligochaete worms (the second most common benthic macroinvertebrate in the Great Lakes). Species were incubated separately and in combination to determine varying organism impacts on sediment mixing and biogeochemistry as well as potential community interaction effects. To simulate deep, offshore conditions, I used low particulate organic matter (POM) sediment in the microcosms and kept them in the dark and at 4°C. I found that sediment mixing depth and intensity varied significantly among species, but that there were no significant differences in sediment oxygen penetration depth or nutrient dynamics. Additionally, I found no evidence for species interaction effects. Finally, I used a Dynamic Energy Budget (DEB) model to explore quagga mussel physiology and growth rates under variable temperatures and food quantities (chapter 4). First, I simulated quagga mussel growth at annual temperatures and food availability representative of oligotrophic, mesotrophic, and eutrophic conditions in nearshore, mid-depth, and offshore regions of the Great Lakes. I then simulated mussel growth under three climate warming scenarios (+0.5°C, +1°C, and +2°C water temperatures). Corresponding changes in lake stratification regime under warming scenarios included an increase in the duration of summer stratification and a decrease in the duration of winter stratification. I found that quagga mussel growth increased with warmer water temperatures and altered stratification regimes. I also found that relative importance of water temperature and food availability varied over trophic status and mussel age, with mussel sensitivity to food limitation increasing as mussels grew larger over time. The combined results from these three studies indicate that quagga mussel impacts on pelagic energy and nutrient dynamics are mostly due to direct mechanisms – including carbon and nutrient ingestion, sequestration, and regeneration – rather than altered sediment geochemistry. My results provide detailed information on quagga mussel physiology, including variability of internal stoichiometry and growth under a wide range of environmental conditions, which strongly influences mussel nutrient recycling. Together, these results improve the current understanding of quagga mussel biology and will help to inform estimates of quagga mussel impacts on biogeochemical cycling in the Great Lakes and other invaded ecosystems.
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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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    Proceedings of the 1st Agricultural Drainage and Water Quality Field Day
    (2002-08-14) Strock, Jeffrey S.; Baker, Jim; Busman, Lowell; Gupta, Satish; Moncrief, John; Randall, Gyles; Russelle, Michael; Taylor, Elwynn