DOC AS A DRIVER OF MICROBIAL DIVERSITY IN AN EAST TEXAS FLUVIAL NETWORK

Freshwater stream ecosystems are rich in microbial life and various environmental factors may influence the diversity of these microbial communities. By virtue of the continuous flow of water from upstream to downstream, rivers form a metacommunity that is linked by downstream dispersal of organic materials and microorganisms. River ecosystems are further complexed with microhabitats such as the benthic zone and the water column. Drawing from ten months of sample data collected from a forested headwater site, this study analyzed correlations between microbial diversity and nine potential drivers: dissolved organic carbon (DOC) concentration and composition, centimeters of rainfall, river kilometers, and water chemistry (total nitrogen, nitrate, and phosphorous). It was found that the diversity of benthic samples was positively correlated with spectral slope ratio and no other variable, while water column diversity was correlated with SUVA254, DOC, rainfall, and negatively correlated with phosphorous in the temporal study. Microbial diversity patterns were also analyzed along a longitudinal continuum (upstream to downstream). The diversity of water samples was found to be positively correlated with Sr, DOC, and river kilometers in the longitudinal study. A clear pattern emerged in which there was higher diversity at the unimpacted large river site than in the headwater sites, but that diversity began decreasing once the river flowed into an artificial reservoir, and especially so downstream of the dam itself.