Thesis (M.A.)--Boston University
PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The natural gradient of eutrophic conditions that exists in Waquoit Bay, (Cape Cod, Massachusetts) allowed us to examine how key biogeochemical processes respond to eutrophication over time. Using a space-for-time substitution we measured oxygen (O2), nutrient, and di-nitrogen (N2) gas fluxes from sediments collected at four stations. The objective of this study was to assess how sediment metabolism, nutrient cycling, denitrification and the balance between N and P limitation may change over a trajectory of increasing eutrophication. In addition, for two sites we compared our more recent measurements to those made in the bay nearly 20 years ago (1992-1994). While we did not find a spatial pattern that was linearly linked to nitrogen (N) loading, our results show characteristics of a system in change. Sediment oxygen consumption was measured at 45% of its historic rate and ammonium flux at only 30%. The difference in net denitrification rate was particularly large, as our mean rate (29.9 µmol N2-N m-2 h-1) was considerably lower than the mean historic value (172 µmol N2-N m-2 h-1). This 83% reduction represents the substantial dampening of a key microbial process for the removal of reactive nitrogen from the ecosystem. Additionally, at our most impacted site, North Basin, we measured significant rates of net N fixation, indicating that the sediments are becoming a net source of reactive N. In another important example of change, we observed an anomalous efflux of phosphate (PO4 3-) from the sediments during the summer and high ratios of both oxygen uptake to phosphate release (O2:PO4 3-) and ammonium to phosphate release (NH4+:PO4 3-). This unexpected result suggests that, at least in some times of year, Waquoit Bay may be co-limited by both nitrogen (N) and phosphorus (P). If these observations of N and P co-limitation hold into the future, it will have important consequences for the ecology and management of this coastal system.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/12387 |
| Date | January 2012 |
| Creators | Foster, Sarah Quinn |
| Publisher | Boston University |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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