Sediment and microplastic accumulation in stream systems occur when particulates entrained in overbank flow are retained by the floodplain. Despite overbank flow conditions dictating sediment and microplastic accumulation, the spatial distribution of accumulation within floodplains remains poorly understood. Difficulty quantifying hydraulic flow conditions is due to spatial variation introducing erroneous error. This study hypothesized floodplain sediment and microplastic accumulation would be closely correlated with topographic, vegetative, and hydraulic conditions. To test this hypothesis, sediment and microplastic accumulation were measured along a 1.25 km stretch of Stroubles Creek in Blacksburg, Virginia. Sediment accumulation was measured using tiles with a surface area of 144cm² at 75 locations. Tiles accumulated 4,782g over their two-year deployment. Microplastic accumulation was assessed by taking 15cm3 soil grab samples from 40 locations. Microplastics were identified using FTIR spectroscopy and were found to have a concentration of approximately 7MPm-3. Topographic and vegetative variables were measured using digital elevation and canopy height models, while hydraulic variables were calculated with an unsteady flow model in HEC-RAS. Sediment and microplastic accumulation were both found to be significantly influenced by terrain and hydraulic conditions. Sediment accumulation yielded an MLR model with an R2 of 0.72, with a confidence level between 97% - 99%, while the microplastic model yielded an R2 of 0.26 and with a confidence level between 95% - 98%. Differences in sediment and microplastics particle density resulted in hydraulic conditions being more influential on microplastic accumulation with an R2 81.5% greater than any its terrain components. This research identified floodplain accumulation process drivers which could help to guide future management decisions regarding sediment storage and monitoring microplastic accumulation. / Master of Science / Streams act as natural thoroughfares, with the potential to transport materials beneficial and harmful to biological and environmental processes. During flood events, the material carried by stream flow is often deposited in areas adjacent to the main channel. These adjacent areas are called floodplains and contribute to the accumulation of sediment and small pieces of plastic in stream systems. Spatial patterns in floodplain accumulation are believed to be the result of site-specific terrain, vegetation, and flow conditions within a stream system. In the context of a stream system, descriptive characteristics of terrain, vegetation, and flow conditions are heavily confounded making their relationship with floodplain accumulation difficult to interoperate. This study aims to understand the accumulation of sediment and plastics in the Stroubles Creek floodplain by evaluating the terrain, vegetative, and flow conditions believed to influence systematic patterns in accumulation. Floodplain sediment and plastic accumulation were measured along a 2 km reach of Stroubles Creek at 75 and 40 sampling locations. Terrain, vegetative, and flow conditions at each of the sediment (75) and plastic (40) sampling locations were determined to be the characteristics driving their relative accumulation process. The distance and change in elevation of the sampling locations from the channel, flow velocity of water, arrival time and duration of time each location experienced floodwaters were observed to have the most significant impact on accumulation processes. However, the degree to which each of these variables affected sediment and plastic accumulation differed. These findings suggest that sediment and plastic accumulation are both heavily influenced by terrain and flow conditions; however, the processes by which sediment and microplastics accumulate in the floodplain are likely to differ.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/120657 |
| Date | 11 July 2024 |
| Creators | Smith, Tyler Camden |
| Contributors | Biological Systems Engineering, Hession, William Cully, Czuba, Jonathan A., Stewart, Ryan Daniel |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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