Tidal freshwater wetlands are often found near urban centers, and as a result of human development they are subject to multiple environmental stressors. Increases in nutrient runoff, sedimentation, and hydrologic alterations have had significant impacts on these systems and on the ecosystem services they provide. One of the consequences of these stressors is the expansion of invasive species that can affect native biodiversity and the many biogeochemical processes that are key to wetland ecosystem function. This research looked at how human activities affect microbial communities in tidal freshwater wetlands, and explored various aspects of an invasive plant’s ecology in the Chesapeake Bay.

In our first study, we found that microbial community composition differed along a rural to urban gradient and identified microbial taxa that were indicators of either habitat. Rural sites tended to have more methanogens and these were also indicators in these system, whereas in urban systems nitrifying bacteria were the main indicator taxa. This study suggested that urban wetlands have different microbial communities and likely different functions than those in rural areas, particularly concerning nitrogen and contaminant removal. Our second study looked at management of an invasive lineage of Phragmites australis which is commonly found in wetlands impacted by nitrogen enrichment. We evaluated the effects of different C:N ratios on the competitive ability of this lineage and a native North American lineage. Even though carbon addition did not improve the native’s competitive ability, we identified facilitative interactions when both lineages were growing together. This suggests that native and invasive Phragmites might coexist if there are no additional disturbances to the system. Our last study focused on plant-fungal interactions, and found that both Phragmites lineages benefitted from inoculation with fungal endophytes under salt stress. These results suggest that studies of plant-fungal interactions can yield insights into mechanisms of invasion, and could be further investigated in native wetland plants susceptible to increased salt stress following sea-level rise. Our results provide insights into plant and microbial ecology in the Chesapeake Bay’s tidal freshwater wetlands, and improve our understanding of the invasion process and management strategies of Phragmites australis.