Floods and nutrients in Weeks Bay, AL: an evaluation of long-term environmental change and human impacts on coastal estuaries

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University of Alabama Libraries

Climate change and sea level rise are major concerns for coastal environments, with predicted increased storm intensity, coastal erosion, and ecological degradation. Long paleoenvironmental records can advance our understanding of these effects and help improve coastal resiliency to future sea level rise and climate change. Sediment archives are employed to build long paleo-environmental records for Weeks Bay, Baldwin County, AL. Grain size, organic carbon and nitrogen stable isotopes, elemental composition, and diatom assemblage and abundance are integrated to construct a multi-proxy paleoenvironmental record covering the past ~7000 years, from the Mid-Holocene to present based on 14C and 137Cs ages. The δ13C and δ15N, grain size, and terrestrial and marine elemental proxies indicate flooded marine conditions during the formation of the bay approximately 6600 years ago, and a transition from a more marine-influenced environment to a more brackish/freshwater bay environment as the estuary became more restricted approximately 2000 years BP. Anthropogenic influence in Weeks Bay over the past 200 to 300 years is expressed as changes in redox and nutrient-associated elemental proxies (Fe, Zn, Mn, Cr, V) with increase in C and N weight percent. Comparisons of TOC:TN to the Redfield Ratio confirms that nitrogen is a limiting factor in Weeks Bay, meaning nitrogen from anthropogenic sources potentially increased ecological feedback, signified by algal blooms. 34 flood events were interpreted from sand layers in the last 2000 years, with two periods of high flood activity coinciding with the Medieval Climate Anomaly and the Little Ice Age, illustrating potential correlation between geologically short-term climate changes and storm events. Stricter management of agricultural and industrial run-off with increased wetland conservation can aid in the reduction of algal blooms in Weeks Bay. Paleoenvironmental record studies of Weeks Bay and other estuaries across the Northern Gulf of Mexico help build a more complete understanding of past and present response of estuaries to sea level and climate events, which can be used to better predict their future.

Electronic Thesis or Dissertation
Paleoclimate science, Sedimentary geology