Surface and small-scale processes of biogeochemical cycling of organic matter in tidal sediments

UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
Gwendolyn A. Shaughnessy (Creator)
Institution
The University of North Carolina Wilmington (UNCW )
Web Site: http://library.uncw.edu/
Advisor
Courtney Hackney

Abstract: Despite their exceptionally high productivity, freshwater and oligohaline tidal marshes are rarely studied in terms of their biogeochemistry because of their highly variable and diverse conditions. Such environments are particularly interesting because they experience salinity variations that can dramatically alter biogeochemical processes. Sediment cores were collected on a monthly basis over the course of one year from three substations (intertidal mud flat, marsh, and marsh/upland edge) of an oligohaline tidal marsh in the Cape Fear River Estuary, North Carolina. Depth profiles of redox-active remineralization products (O2, Fe2+, Mn2+, and HS-) were generated with microelectrode-based voltammetry, allowing for high-resolution (millimeter scale) assessment of small-scale microbial processes often overlooked in biogeochemical studies. Oxygen (and attendant aerobic respiration), when present, was limited to less than 7 mm below the sediment-water interface at all three substations. Low quantities of labile organic matter limited remineralization processes to Mn reduction in the upper 10 cm of the intertidal mud flat sediments; Fe reduction and sulfate reduction play apparently minor roles. While Mn reduction has previously been shown to dominate organic matter remineralization in some coastal marine sediments, this study demonstrates that this process is also important in intertidal mud flat sediments. Seasonal trends emerged in the biogeochemistry of the marsh substation due to sediment-root interactions, in which sulfate reduction dominated in spring and summer, Mn reduction in fall, and methane production in winter. Marsh/upland edge sediments were highly influenced by subsurface hydrology and plant physiology, resulting in a biogeochemical mosaic of overlapping microenvironments dominated by different remineralization pathways (Mn reduction, Fe reduction, sulfate reduction, methanogenesis). Biogeochemistry at this substation reflects changes in environmental conditions on short time scales due to subsurface hydrology, tidal inundation, plant physiology, rainfall, and labile organic matter content. These sites and their varied biogeochemistry are likely to represent transitional environments expected to result from sea level rise. The great complexity of these environments, as demonstrated in this study, creates challenges for predicting the role that transitional wetlands will play in carbon storage and the release of greenhouse gases.

Additional Information

Publication
Thesis
A Thesis Submitted to the University of North Carolina at Wilmington in Partial Fulfillment of the Requirement for the Degree of Masters of Science
Language: English
Date: 2009
Keywords
Biogeochemical cycles, Biological systems, Water quality--Environmental aspects
Subjects
Biogeochemical cycles
Water quality -- Environmental aspects
Biological systems