Date of Award


Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)


Biology/Environmental Biology

First Advisor

Jennifer Bowen

Second Advisor

Robert Chen

Third Advisor

Alan Christian


Salt marshes provide a disproportionate amount of ecosystem services relative to other terrestrial habitats, however, in spite of their importance salt marsh ecosystems remain under threat from global change drivers including sea level rise and increased nutrient loading. Microbes are the main mediators of biochemical reactions that affect delivery of many important ecosystem services, especially nutrient removal. Sea level rise and nutrient loading are expected to alter physiochemical conditions and the distribution of habitat types within marsh ecosystems, which may in turn affect the structure of microbial communities. Understanding how abiotic conditions affect microbial community structure is a challenge, however, because chemical gradients in oxygen, carbon, and nitrogen in marsh sediments vary on millimeter scales. The goal of my research was to examine, at very fine spatial scales, the effect of abiotic conditions and habitat type on (1) the structure of total and potentially active salt marsh sediment bacterial communities, (2) the community structure and abundance of functional genes responsible for several key geochemical processes, and (3) the community structure of genes responsible for the processes that produce and consume the greenhouse gas nitrous oxide in salt marsh sediments. My findings show that total and potentially active bacterial communities vary at millimeter scales in salt marsh sediments and that both habitat type and depth play key roles in structuring bacterial communities. The community structures of the genes responsible for the geochemical processes denitrification, sulfate reduction, and the dissimilatory reduction of nitrate to ammonium, are also strongly influenced by habitat and depth. Finally, my results show that the processes that produce and consume nitrous oxide in salt marshes are affected by nitrogen content, with little influence of habitat or depth. These data suggest that microbial communities respond to millimeter scale changes in salt marsh sediments and that microbial communities are sensitive to changes in habitat and abiotic conditions. Any changes in microbial communities due to habitat shifts and altered sediment chemistry resulting from sea level rise and nutrient loading, especially among nitrogen cycling organisms, may potentially have severe consequences for the delivery of ecosystem services afforded by salt marshes.


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