Browsing by Subject "Uptake"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item The effects of fluid flow and epiphytes on submerged aquatic vegetation(2012-05) Hansen, Amy ThereseThe intent of this research was to investigate the effects of fluid flow characteristics and epiphyte colonization on submerged aquatic vegetation (SAV) photosynthesis and dissolved material uptake. SAV, with its stems and leaves completely submerged in the water column, is strongly affected by both the physical characteristics of the water, such as dissolved material concentrations and fluid motion, and by factors that alter its interaction with the water, such as epiphyte colonization of SAV surfaces. The nature of these interactions was investigated through a series of four separate studies. First, through a laboratory mesocosm experiment, epiphyte uptake and SAV uptake of a dissolved contaminant (nickel) were shown to occur at different rates and due to different mechanisms. Second, a model of photosynthetic rates, based on mass transfer theory, was developed requiring only three parameters that accounted for the effect of water motion on photosynthetic rates. This model was experimentally validated with dissolved oxygen and velocity profiles over blades of giant kelp, Macrocystis pyrifera. Third, using two separate microscale velocity imaging methods, photosynthesis was shown to alter fluid motion near the surface of a Cladophora spp. filament by more than doubling velocity gradients and thus surface shear stress. In this investigation, bacterial epiphytes had no effect on shear stresses but assemblages consisting primarily of diatom epiphytes strongly decreased the surface shear stress from what would have been experienced during photosynthesis without epiphytes present; indicating a harmful interaction with epiphytes. Fourth, in agreement with the microscale results in the third study, epiphyte removal was shown to increase local dissolved oxygen concentrations throughout the water column as well as decrease water column soluble reactive phosphorus concentrations due to higher photosynthetic rates in field research in a constructed wetland. In a related laboratory study, epiphyte detachment rates were functionally related to water velocity. Overall, I have shown through laboratory and field experiments that SAV photosynthesis is closely linked to fluid flow characteristics, SAV and epiphyte uptake are not equally affected by flow conditions, and epiphyte colonization decreases SAV photosynthetic rates.Item Measurement and modeling of denitrification in sand-bed streams of varying land use(2013-02) Guentzel, Kristopher StevenProcesses that govern transport and transformation of aquatic nitrogen are of growing importance due to increases in anthropogenic nitrogen input from fertilizer application and fossil fuel combustion. Denitrification, the incremental reduction of soluble nitrate to gaseous end products, is the main pathway in which nitrogen is biologically removed from aquatic ecosystems. In this study denitrification is measured from sediment cores in five streams in central Minnesota, USA, using denitrification enzyme activity (DEA) assays as well as microbiological techniques including the amplification of nirS gene fragments through qPCR. Hydraulic and environmental variables are measured in the vicinity of the sediment cores to determine a possible mediating influence of fluid flow and chemical variables on denitrification activity. Denitrification rates measured using DEA analysis with amended nutrients ranged from 0.02-10.1 mg-N m-2 hr-1. Denitrification rates measured without amended nutrients were a factor of 5.35 less on average and ranged from 0.03-0.98 mg-N m-2 hr-1. The abundance of the denitrifier gene nirS was positively correlated with denitrification potential measurements (R2 = 0.79, P < 0.001) for most of the streams studied. NirS distribution in one of the sites, a field scale experimental stream called the Outdoor StreamLab, followed the spatial distribution of benthic organic matter closely along the sediment bed and through the sediment column. Predictive models to determine nitrate uptake via denitrification were derived from hydraulic, morphologic and water quality variables. The first used hydraulic data collected over three summers in the Outdoor StreamLab. A Gaussian-type function was fit to these data and was dependent on fluid flow and channel characteristics within the stream system. The second model was derived following dimensional analysis on data from the Outdoor StreamLab and four other natural streams of varying watershed and in-stream conditions. This predictive model integrated not only stream hydraulic data but also environmental, morphological and DEA measurements for nutrient-amended and unamended samples. The proposed model explained 75% and 60% of the variability in amended and unamended DEA rates, respectively. Results from this study verify that denitrification is ubiquitous across varying stream systems but is most dependent on the distribution of sediment organic matter and interstitial pore space as well as stream hydraulic characteristics.