Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item MODELING IMPACTS OF SUBMERSED AQUATIC VEGETATION ON SEDIMENT DYNAMICS UNDER STORM CONDITIONS IN UPPER CHESAPEAKE BAY(2019) Biddle, Mathew Michael; Sanford, Lawrence P; Palinkas, Cindy; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Submersed aquatic vegetation is an important modulator of sediment delivery from the Susquehanna River through the Susquehanna Flats into the Chesapeake Bay. However, the impact of vegetation coupled with the physical drivers of sediment transport through the region are not well understood. This study used a new vegetation component in a coupled flow-wave-sediment transport modeling system (COAWST) to simulate summer through fall 2011, when the region experienced a sequence of events including Hurricane Irene and Tropical Storm Lee. Fine sediment was exported under normal flows and high wind forcing but accumulated under high flows. The relative effect of vegetation under normal and high wind forcing depended on previous sediment dynamics. Vegetation doubled the accumulation of fine sediments under high flows. While further refinement of the bed model may be needed to capture some nuances, the COAWST modeling system provides new insights into detailed sediment dynamics in complex vegetated deltaic systems.Item Sediment connectivity between the lower Susquehanna River and upper Chesapeake Bay(2019) Russ, Emily; Palinkas, Cindy; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Excess fine sediment is one of the main pollutants contributing to water quality degradation in the upper Chesapeake Bay. Recent management efforts have focused on reducing sediment inputs within the Bay watershed to achieve water quality standards set in the Chesapeake Bay Total Maximum Daily Load (TMDL). However, the models used to develop the TMDL did not account for the evolving sediment loads to and storage in the Bay, which include reduced sediment capacity in the Conowingo Reservoir, the last reservoir on the Susquehanna River, increased shoreline protection measures, and resurgence of SAV in the upper Bay in a region known as the Susquehanna Flats. The overall goal of this dissertation is to assess the current sediment dynamics of the upper Bay and specifically evaluate the connectivity of sediment transport from the Susquehanna River through the Flats into the upper Bay. First, I evaluated sedimentation on the Susquehanna Flats over seasonal to decadal time scales using radioisotopes within the context of submersed aquatic vegetation (SAV) biomass and geomorphology. Seasonal-scale sedimentation variability was related to river discharge, sediment supply, and geometry over the SAV bed, while decadal-scale sedimentation was influenced by flood events and changes in SAV biomass abundance. Next, I analyzed sediment geochemical patterns in the upper Bay using statistical analyses. Elements associated with aluminosilicate minerals, rare earth elements, and heavy metals explained the most variability in the dataset due to changes in grain size, salinity, and anthropogenic input, respectively. A sediment-provenance analysis was performed using the sediment-geochemistry data and indicated that the Susquehanna is the dominant source of fine-grained material throughout the upper Bay. Finally, I developed an updated sediment budget through quantitative analysis of sediment sources (Susquehanna River and shoreline erosion) and sinks (Susquehanna Flats and mainstem sediment-accumulation rates). Conservation-management practices have reduced Susquehanna River sediment loads at low flows, but sediment loads at high flows have increased, consistent with a decreasing scour threshold for bottom sediments in Conowingo Reservoir as it has filled. Increases in shoreline stabilization have reduced shoreline erosion inputs.Item SUGARCANE AGRICULTURE AS AN AGENT OF GEOMORPHIC CHANGE AND STREAM DEGRADATION IN BRAZIL(2017) Ometto Bezerra, Maira; Palmer, Margaret A; Filoso, Solange; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intensive agriculture profoundly alters the geomorphology, hydrology and nutrient balances of catchments. The result is the degradation of headwater stream ecosystems via inputs of excess sediments, surface runoff, and nutrients. To mitigate the negative effects on streams, watershed managers can implement riparian buffers, which are designed to intercept, process, store, and remove excess material from upslope agricultural source areas. While extensive research on those topics exists for temperate regions of developed countries, little is known in tropical regions of developing countries. To address this knowledge gap, I investigated the effects of sugarcane agriculture on catchment geomorphology and headwater stream ecosystems in Brazil. I studied 11 first and second order catchments spanning a sugarcane-forest gradient near Piracicaba, SP, to answer three main questions. (1) Is sugarcane agriculture an important agent of geomorphological change via gully formation? (2) Does gully formation influence the effectiveness of riparian buffers while increasing the stream response to storm events, and the amount of sediment in high flows? (3) Can land cover history in terms of sugarcane, and forest cover explain the variability in stream nutrient (nitrogen and phosphorus) concentrations? The overall results suggest that sugarcane agriculture is a driver of geomorphic alteration via gully formation in small order catchments in Brazil. Gullies act as effective conduits of surface runoff from upslope source areas to streams, increasing the magnitude of the stream’s response to storms and the amount of sediment transported in high flows. Consequently, gully formation may overwhelm any protective role played by riparian buffers. Sugarcane agriculture also increases stream nutrient concentrations to a point rarely recorded for streams draining intensive cropping in Brazil. However, there is little evidence that forested riparian buffers significantly mitigates the extent to which sugarcane agriculture affects stream nutrient concentrations. Additional policies to the restoration of riparian forests are needed to effectively protect headwater streams in Brazil.Item Comparison of Hydrologic and Hydraulic Characteristics of the Anacostia River to Non-Urban Coastal Streams(2016) McDowell, Mallori; Prestegaard, Karen L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Streams in urban areas often utilize channelization and other bank erosion control measures to improve flood conveyance, reduce channel migration, and overbank flooding. This leads to reductions in evapotranspiration and sediment storage on floodplains. The purpose of this study is to quantify the evapotranspiration and sediment transport capacity in the Anacostia Watershed, a large Coastal Plain urban watershed, and to compare these processes to a similar sized non-urban watershed. Times series data of hydrologic and hydraulic changes in the Anacostia, as urbanization progressed between 1939-2014, were also analyzed. The data indicates lower values of warm season runoff in the non-urban stream, suggesting a shift from evapotranspiration to runoff in urban streams. Channelization in the Anacostia also increased flow velocities and decreased high flow width. The high velocities associated with channelization and the removal of floodplain storage sites allows for the continued downstream transport of sediment despite stream bank stabilization.Item Ecological and geomorphological impacts of channel stability restoration in urban streams(2011) Laub, Brian Guthrie; Palmer, Margaret A; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream restoration projects that attempt to reduce channel incision and bank erosion by reconstructing the channel and grading and armoring stream banks (channel stability restoration projects) are common, particularly in urbanized watersheds. However, integrated assessment of changes in geomorphic processes and ecological properties within the channel and in the surrounding riparian zone induced by stability restoration has rarely been carried out across multiple restored streams. I provide such an assessment by measuring channel complexity, bed sediment dynamics, channel movement rates, riparian soil structure and function, and diatom communities in multiple restored streams located in urbanized watersheds and comparing these measurements to measurements from urban and forested reference streams. Stability restoration appears to have reduced lateral channel migration and channel incision through channel reshaping. Patterns of bed sediment movement were altered through the effects of added channel obstructions on flow dynamics and bed sediment size distribution. Channel stability restoration did not alter channel complexity, primarily because channel complexity was not reduced by urbanization as has commonly been assumed. Restoration did not alter diatom communities either, primarily because diatom communities responded more strongly to urbanization-induced changes in water chemistry. Riparian soils were negatively impacted by stability restoration, particularly compared to riparian buffer establishment, which had mostly neutral effects on riparian soils. Channel stability restoration can provide a minor increase in channel and bed sediment stability. However, changes in bed sediment stability were driven by in-channel restoration structures, which can be placed without grading the banks or reconstructing the channel. Riparian buffer restoration can also stabilize channels and will provide wood to channels, which can provide similar stabilization benefits as restoration structures. Restoration of channel stability using only in-channel structures and riparian vegetation planting would reduce the cost of stability restoration and reduce negative impacts to riparian soils. Even so, effects of stability restoration were often overwhelmed by processes operating beyond the channel boundaries, suggesting that reach-scale targeting of channel instability needs to be assessed at the watershed scale and may need to be given lower priority to such restoration approaches as stormwater management, which directly address the causes of channel instability.Item EFFECTS OF CHANNEL MORPHOLOGY ON FLOODPLAIN INUNDATION AND SURFACE-GROUNDWATER INTERACTIONS IN AN URBAN WATERSHED(2011) Lundberg, Dorothea June; Prestegaard, Karen L.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this study is to evaluate groundwater-surfacewater interactions between a stream and the adjacent floodplain. The study site includes two reaches on Paint Branch Creek: an incised reach with inset gravel bars and a non-incised reach with active accretion of gravels bars onto the floodplain and off channel features. Topography, sediment grain size and hydraulic conductivity, groundwater head, and floodplain/channel characteristics were measured. Groundwater head data in gravel bars and adjacent floodplains were monitored for one year to determine seasonal variations in groundwater flow directions, rates, and to develop groundwater probability curves. Identification of groundwater-surfacewater interactions and off channel features roles was determined. In the reach with attached gravel bars, water flows from the creek into the adjacent gravel bars for the most of the year. Evapotranspiration and tropical storms influence seasonal reversals in flow directions between the gravel bar and the floodplain.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.