Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item Morphology in Urbanized Streams of the Puget Sound Lowland Region(2004) Boyle, Pamela; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this research is to evaluate the effects of urbanization on channel morphology. Three hypotheses are tested: 1) Channel morphology measured from one cross section is not similar to reach-averaged values, 2) Channel shear stress ratios and erosivity increase with urbanization, and 3) Channel morphological complexity decreases with urbanization increases. Results indicate that single cross-section data do not adequately describe channel morphology. Shear stress and bed mobility did not increase with urbanization, perhaps due to the presence of large bed grain sizes that adjust to increases in flow. Similarly, channel complexity did not decrease with increased urbanization. These data indicate that channel changes resulting from urbanization are influenced by sediment supply as well as discharge, and that this should be taken into consideration in restoration design.Item MORPHOLOGY IN URBANIZED STREAMS OF THE PUGET SOUND LOWLAND REGION(2004) Boyle, Pamela Roxana; Prestegaard, Karen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Increased runoff from urbanization may result in erosion to the stream channel and banks, leading to channel incision, bed changes, loss of instream debris and habitat, and an overall reduction of heterogeneity and channel complexity. These impacts are especially evident in low gradient, gravel-bed, meandering streams - the major type of stream in the Puget Sound Lowland region. The failure of many stream restoration projects is due to a lack of understanding of how morphological features of a stream respond to hydrological changes. Single cross-section methods (instead of reach-level) are generally used and may not adequately portray the complexity, or variation, of the stream channel and bed. Three main hypotheses in this thesis are: 1) a single cross-section taken within a reach does not adequately describe a stream compared to a mean value calculated from several measurements; 2) urban streams with more urbanized drainage areas have higher shear stresses, and thus move larger bed particles and have higher reach mobility; and 3) urban channels have less channel complexity than non-urban channels. Results showed that a single cross-section may not adequately describe the morphological variables of a stream reach; however, this method may be appropriate for calculating reach shear stress. In addition, shear stress and mobility were not found to increase with increasing urbanization. Furthermore, complexity was not found to decrease with increasing urbanization. These two latter results indicate that urbanization (or percent imperviousness) alone cannot be used as a variable to investigate changes in stream morphology and hydraulics. In fact, a measure of sediment supply could be considered an additional independent variable by which to study urbanization impacts to streams. Substrate distributions from this thesis also support this finding.Item Importance of channel networks on nitrate retention in freshwater tidal wetlands, Patuxent River, Maryland(2009) Seldomridge, Emily Dawn; Prestegaard, Karen; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Freshwater tidal marshes border stream channels near the upstream end of the tidal limit, and are likely to undergo significant changes in salinity, tidal inundation, and biogeochemical processes due to sea-level rise. Tidal channel networks enhance nutrient processing by delivering nitrate-rich water far into the marsh. The purpose of this study is to examine the geomorphological, hydrological, and biogeochemical processes that influence the delivery and processing of nutrient-rich waters into tidal marshes. In this study, field measurements were made to calculate water and nitrate flux for stream channels of varying order. These mass balance calculations indicate there is an exponential increase in net nitrate retention with channel order. This calculation could be compared with calculations of denitrification at different sites within the system to evaluate the role of these processes in total nitrate loss.