Coastal ecosystems continue to face numerous negative impacts from human activities ranging from local nutrient enrichment to global warming. These threats have complex effects on coastal biogeochemistry, which in turn alters ecosystem ecology and climate. While sediments have long been recognized as cornerstones of marine ecosystem functioning, the impacts of anthropogenic change on benthic biogeochemical cycling remain challenging to constrain. This knowledge gap stems from technological issues as measuring marine sediment processes under natural conditions is a formidable challenge. To help move the field of sediment biogeochemistry forward, I developed a novel mass spectrometer-based system and used it to quantify dissolved gas fluxes from marine sediments.
In Chapter One, I survey the field of underwater mass spectrometry from its inception three decades ago to the present. Through comprehensive descriptions of the current status of the technology, field applications to date, and future trends, I provided guidance for how to leverage this powerful new tool to measure gaseous compounds in the under sampled ocean. In Chapter Two, I review the role of permeable shelf sediments in marine nitrogen cycling. My synthesis of the small but growing body of work on nitrogen cycling in shelf sands exposed conflicting evidence surrounding the nitrogen removal capacity of permeable sediments, and I proposed targeted approaches, such as the development of noninvasive in situ technologies, to resolve these controversies. In Chapter Three, I present a newly developed flow-injection sampling system that can be coupled to a mass spectrometer to measure a range of dissolved gas species in the pore water of highly permeable sandy sediments. Rigorous calibration and validation experiments demonstrate that this novel system can quantify dissolved gas depth profiles, as well as fluxes across the sediment-water interface, in permeable sediments. Furthermore, with my prescribed design improvements, this tool promises to provide in situ data in dynamic sandy environments. In Chapter Four, I used the flow-injection mass spectrometer system to measure benthic fluxes of gaseous nitrogen and methane from cohesive sediments subjected to low oxygen conditions and varying organic matter loads. The unprecedented high temporal resolution of the gas flux data revealed the complex and dynamic effects of changing environmental conditions on the capacity of sediments to remove reactive nitrogen and regulate methane emissions. / 2024-11-08T00:00:00Z
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/45318 |
| Date | 08 November 2022 |
| Creators | Chua, Emily Jingyi |
| Contributors | Fulweiler, Robinson W. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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