| Salt marshes, which are tidally-influenced and reside at the interface between often heavily-developed uplands and the open ocean, are among the most productive ecosystems on the planet and protect the coastal ocean from terrestrially-derived pollution. Microbial communities in salt marshes catalyze most reactions that are characteristic of salt marsh biogeochemistry and thus contribute to salt marsh beneficial functions. As salt marshes are frequently polluted with heavy metals, organic pollutants, and nitrate due to upland development, whether the pollution affects marsh microbial communities, their physical compartmentalization and biogeochemical cycling (e.g. denitrification) are important to know. This dissertation thus examines the relationships between microbial communities, bacterial growth mode and pollutants in estuarine environments, with an emphasis on salt marshes. The results of this research are that: (1) despite high natural variability in the intrinsically complex and dynamic salt marsh environments, both eubacterial and denitrifier community composition are significantly correlated with heavy metal pollution, (2) denitrifiers, and thus denitrification, are selectively advantaged by being particle-associated on the smallest sediment particles where bacteria are embedded in exopolymeric substances and exist within a protective biofilm, (3) the denitrifier community composition, and thus denitrification and its relatedness to common predictors such as population size and organic carbon content, varies within salt marshes due to variations in environmental factors such as salinity from up to downstream, and that (4) microbial communities and the specific operational taxonomic units within community profiles were related to stress factors and thus could be pollution indicators in estuarine environments. This dissertation represents an important characterization of microbial communities and denitrification in salt marshes on the California coast, and demonstrates contributions of small scale heterogeneity to large scale spatial variability in salt marsh microbial processes. Collectively, this dissertation indicates that microbial communities may be a directly-relevant and useful indicators for characterizing salt marsh health. These findings may have important implications in coastal environmental management and general microbial ecology. |
