Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

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2004 - 20102

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Subject: search.filters.subject.Hydrilla verticillata

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    COMPETITION BETWEEN HYDRILLA VERTICILLATA AND VALLISNERIA AMERICANA IN AN OBSERVATIONAL FIELD STUDY AND GREENHOUSE EXPERIMENT.
    (2010) McChesney, Lauren Dalton; Engelhardt, Katharina; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Invasive species continue to have a pervasive influence on biodiversity but it is often unclear how invasive species affect native species. In field observations and greenhouse experiments, I examined the effect of the non-native submersed aquatic plant Hydrilla verticillata on the native species Vallisneria americana. Field monitoring from 2002 to 2006 showed that coverage of species peaked in 2004 after initial invasion of the estuarine study system in 2002. Substrate characteristics did not limit species distribution. In contrast, substrate and planting density affected plant growth and the outcome of intra- and inter-specific competition in the greenhouse. Although other environmental variables, such as water depth and turbidity, appear to override the effect of substrate in the field, the greenhouse experiment suggests that substrate can be an important driver of submersed aquatic plant community dynamics. Sediment characteristics should therefore be a factor in restoration design and the management of invasive species.
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    EFFECTS OF PRE-EXISTING SUBMERSED MACROPHYTES ON THE INVASION SUCCESS OF HYDRILLA VERTICILLATA
    (2004-07-06) Chadwell, Todd Byron; Engelhardt, Katharina; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    I evaluated (1) the effects of a native submersed aquatic plant species, <i>Vallisneria americana<i>, on the colonization success of a non-native and highly invasive submersed aquatic species, <i>Hydrilla verticillata<i>, through field and greenhouse experiments; and (2) the effects of <i>H. verticillata<i> propagule density on its colonization success of patches dominated by the native species. Results of the field study, located in a tidal freshwater region of Chesapeake Bay, suggest that pre-existing vegetation did not have significant negative effects on <i>H. verticillata<i> colonization. However, pre-existing <i>H. verticillata<i> biomass and <i>H. verticillata<i> colonization success were strongly correlated. In contrast, results from the greenhouse study showed that <i>V. americana<i> had a strong inhibitory effect on <i>H. verticillata<i> colonization by fragments and increasing <i>H. verticillata<i> fragment density again increased colonization success. Reduced water column nutrient concentrations, resulting from <i>V. americana<i> growth, appeared to negatively affect successful rooting and subsequent colonization by <i>H. verticillata<i>.