Urban infrastructure affects a critical but often overlooked aspect of stream ecosystems and water quality: bacterial communities. We were interested in learning how different types of urbanization altered stream bacteria along an elevational gradient through multiple seasons. Each of the three watersheds also have reservoirs for water resource management ranging in size from 13.5 km2 to 0.38 km2. We filtered water from high and low elevations above and below the reservoirs in three Wasatch Mountain watersheds in Utah, USA with varying degrees of urbanization at low elevations (dense urban, rapidly transitioning from agriculture, slowly transitioning from agriculture) in August, November, February, and May. We extracted (MoBio Power Soil DNA kits), amplified, and sequenced the 16s rDNA V4 region using 454 or HiSeq and interpreted community composition using MOTHUR and R.
The diversity of the bacterial communities decreased markedly below reservoirs (richness: P<0.001, evenness: P<0.05, and Shannon diversity index: P<0.001; one-way ANOVA) with no difference in diversity metrics between watersheds and season (P>0.05). In a test of community composition (distance), location relative to dam was significant and the interaction of dam and watershed being significant (P<0.001, Anosim) while the interaction of reservoir and season was not (P=0.227). A PCoA analysis of the community structure grouped above reservoir sites more tightly than watershed or season. This suggests that the presence of these reservoirs is a significant disruptor of overall diversity, regardless of downstream land use. The size of the dam and the downstream land uses are likely responsible for shaping the new structure of the affected community, but changes in season and climate are less influential.