Understanding how the fate of carbon is influenced by biological communities is one of the greatest challenges in ecosystem science. Freshwater ecosystems, including streams, are now recognized as sites for the transport, processing, and burial of substantial amounts of organic matter. Communities of microbes, including bacteria, account for a vast majority of the processing of organic matter in streams, but there is much that is not known about how microbial communities impact the fate of organic matter in streams. This project will address this knowledge gap by studying how bacterial community diversity, stream water chemistry, and organic matter composition influence whether organic matter is consumed by stream microbes or transported downstream. A mesocosm experiment will be conducted to test the hypothesis that changes in pH and organic matter composition will impact the stream microbial community and its ability to process organic matter. Genetic bacterial community fingerprints will be used to quantify how the bacterial community responds to the experimental treatments. Bacterial metabolic responses will be measured using enzyme assays and overall metabolic rates.
This project will contribute to understanding of the relationship between microbial community structure and metabolism in freshwaters. As watersheds are altered by human activity, pH and organic matter inputs to aquatic ecosystems are also changing. Since streams may be viewed as sentinels for environmental change, this study will generate insight into the response of freshwater communities to global change. Undergraduate researchers will be engaged in all aspects of the work to further their scientific understanding. Results will be communicated at scientific meetings and in journals. Educational materials will be developed for local primary school students that assist in interpreting this work and broader concepts of ecosystem ecology.
Research was conducted to determine the environmental controls on the community structure and metabolic function of microbial communities in headwater streams. The overall objective of this project was to determine the extent to which the work that microbes do in freshwaters is controlled by environmental constraints versus population dynamics. To accomplish this, the response of microbial community composition in streams to environmental factors including watershed land cover, temperature, hydrology, water chemistry, and organic matter supply was assessed. In turn, the link between community composition and metabolic activity of stream microbes was also investigated. By testing how strongly microbial community composition impacts metabolic function over space and time this research has provided insights into fundamental ecological theory, particularly addressing questions related to microbial functional redundancy. These results can also be applied to inform ecological restoration practices by identifying how the presence and absence of microbial communities are controlled by environmental factors. Research was conducted in eight first order and three second order streams in the Coastal Plain of Maryland. Streams spanned a gradient of urbanization with forest cover ranging from almost 0 to 100 percent. Sediment and stream water microbial communities were analyzed by sequencing bacterial 16s rDNA genes using next-generation sequencing techniques. Microbial heterotrophic activity was determined using extracellular enzyme activity incubations. Activity of seven heterotrophic microbial enzymes was assessed. The quality of dissolved organic matter (DOM), an important energy source for stream microbial communities, was determined using spectroscopic methods. Results indicated that while water chemistry factors, such as pH, that have been previously linked to stream microbial communities were indeed important in forested streams, land cover urbanization and related water chemistry factors including water conductivity and nutrient content were more strongly related to microbial community composition. Some aspects of microbial metabolic function were related to environmental factors including urbanization which was positively related to enzymes targeting organophosphate compounds. Other microbial metabolic enzymes were more strongly linked to microbial community composition. This suggests that at least some aspects of microbial heterotrophic metabolic activity are not redundant across all communities within these headwater streams. Thus, this project has contributed to fundamental ecological theory by further knowledge of the links between microbial structure and function in stream ecosystems. By identifying environmental factors that impact microbial function, this research will also help inform future ecological restoration practices. This research has already resulted in four conference presentations, an invited panel presentation, four public outreach talks to both teachers and the general public, and a research article, which has recently been accepted for publication. Additional research articles based on this work are currently being prepared. Results from this research have also been conveyed to the public in two articles published by our partners at the American Chestnut Land Trust. Knowledge gained from this work is also being adapted for additional educational programs.
