Graduate Thesis Or Dissertation

Geochemical cycling in a Pacific Northwest estuary (Tillamook Bay, Oregon, USA)

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  • This thesis investigates the behavior of major inorganic nutrients (P, N, Si), trace metals (Mn, Fe), and alkaline-earth metals (Ba) within Tillamook Bay over seasonal cycles and under a range of river discharge conditions from October 1997 through December 1999. Located in the Pacific Northwest region, Tillamook Bay is an ideal system for evaluating biogeochemical cycling along the river-estuary-ocean continuum and over seasonal cycles. The estuary experiences, on average, a 30-fold decrease in freshwater discharge from winter to summer due primarily to changes in precipitation. Additionally, the oceanography of this region is strongly influenced by the process of coastal upwelling. Results presented here suggest that seasonal processes occurring at both the river and ocean end-members influence elemental estuarine behavior. Based on estuarine distributions and box model calculations, elemental behavior within the estuary is best explained by four factors: freshwater flushing time, biological uptake, interaction with suspended particulate material, and benthic regeneration. Freshwater flushing time, which is largely influenced by river discharge, determines the amount of time for biological uptake, exchange with suspended particles, and interaction with the sediments. Superimposed on these estuarine processes is the seasonal influence of coastal upwelling on biogeochemical processes within the estuary. The results of this research highlight the importance of estuarine processes in modifying the riverine flux of these elements to the ocean. This study also underscores the necessity of temporal sampling in evaluating processes controlling elemental distributions within estuaries and the delivery of land-derived material to the coastal ocean.
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