Browsing by Subject "Environmental factors"

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    Factors contributing to cyanobacteria blooms in Upper Saint Croix Lake, WI
    (2012-12) Pevan, Thomas William
    Upper Saint Croix Lake is a small, shallow, eutrophic lake that has experienced anthropogenic eutrophication. Nutrients, and in particular phosphorus availability, have long been recognized as a factor influencing the water quality of lakes. If phosphorus is excessive, cyanobacteria are often favored, leading to significant negative implications for the overall water quality and biodiversity of the lake, recreational enjoyment, and human and animal health. Nutrient concentrations, environmental factors, and phytoplankton efficiency were assessed to determine the role of seasonality and associated factors in the development of cyanobacteria blooms, and to examine the influence of year to year variability on the seasonal dynamics of the phytoplankton community. Light measurements, water temperature, and water samples were collected during the summers of 2008 (only year with a significant cyanobacteria bloom), 2009, and 2010, along with some winter sampling in 2010. Chemical analyses included chlorophyll a, particulate phosphorus, soluble reactive phosphorus, total and total dissolved phosphorus, total and total dissolved nitrogen, ammonia, nitrate, and soluble reactive silica in addition to active fluorometry (Phyto-PAM and Fluoroprobe). Results indicate that cyanobacteria in Upper Saint Croix Lake are controlled ultimately by phosphorus, and to a lesser degree, nitrogen and water temperature. Phosphorus concentrations, are in turn, controlled by environmental factors (precipitation, outflow, and inflow) that manipulate the dilution and flushing rate of the phosphorus present in the lake.
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    Seed size in lacustrine and riverine populations of wild rice (Zizania palustris)
    (2010-10) Eule-Nashoba, Amber Rae
    To study the effects of the hydrological regimes of lakes and rivers on seed size of wild rice (Zizania palustris), four lakes and four rivers were sampled to measure and model the factors affecting seed size. Based on casual observation by harvesters and biologists it has been hypothesized that seeds produced in riverine habitats are smaller than those produced in lacustrine habitats. We found mean seed mass in lake populations was 15.4 mg (41%) larger than in river populations. When seed mass was partitioned between water body type, regional population pair, and individual population, water body type accounted for 71.3% of the variance. Data collected on seed mass, panicle density, seed scars, root mass, sediment characteristics, and water depths were used to create a statistical model to quantify the effects of each factor on seed size. The two most important environmental factors contributing to seed size were sediment bulk density and water depth at seed collection. Important biological components were seed scar density, proportion of filled seed, and root dry mass.