Nutrient and Trace Element Contents of Stream Bank Sediments from Big Spring Run and Implications for the Chesapeake Bay
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The primary goal of this work is to develop analytical methods to determine the origin and fate of phosphorus (P) and other trace elements in stream bank sediments, including those informally termed “legacy sediments”. Legacy sediments were deposited during the historic, post-settlement period due to intense land clearing, deforestation, and the construction of numerous milldams, which occur in high concentrations in the mid-Atlantic region, and constitute substantial volumes of sediment stored in stream corridors. Understanding the concentration of P in fine-grained sediment, and its availability for biological uptake, is important in predicting downstream effects caused by erosion of stream banks and associated legacy sediments. To investigate these processes, stream bank samples were mechanically processed and separated into three size fractions: -230, -180, and +230. These fractions were partially digested using the EPA 3051 method, and then analyzed for sorbed trace metals and P using an Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES). Concentrations for major and trace elements for the -180 fraction were also obtained using X-ray fluorescence (XRF) spectrometry. A settling experiment was devised to mimic the effects of the resuspension of stream bank sediment in waterways. These analyses revealed that the stream bank sediments at Big Spring Run contain an average of 770 ppm P, of which roughly 70% of the environmentally available P is the finest sediment fraction (-230). Nutrients, preferentially bound to such fine-grained sediments, are more prone to be transported through water systems as suspended particles. The high concentrations of sorbed, or environmentally available, P and its attachment to large volumes of fine-grained particles indicates that as legacy sediments enter streams, P could become available for plant uptake under reducing conditions, supporting the hypothesis that bank erosion can be a significant source of P to, and a potentially substantial cause of eutrophication in, the Chesapeake Bay. In addition, it is shown that trace element concentrations in the stream bank sediments at Big Spring Run are strongly controlled by cation exchange processes and/or by formation of complex sorption bonds with Fe-Al compounds – probably oxyhydroxides -- with an overprint of anthropgenic enrichments observed in many trace metal profiles. Magnetic susceptibility of the stream bank provided additional information regarding anthropogenic impacts on soils in the Big Spring Run watershed.
Franklin and Marshall College Archives, Undergraduate Honors Thesis 2008
- F&M Theses Collection