Variations in Stream Sediment Microbial Communities Across a Natural Climate Gradient in Eastern Puerto Rico

Abstract

Six months following the passage of Hurricane Maria across Puerto Rico, water and sediment samples were taken at eight locations along a precipitation gradient to assess the impact of sediment upwelling, organic matter input, and other heavy precipitation-associated influences on water chemistry and microbial populations. Eight sites were broken up into wet (291-440 cm precipitation/yr), dry (140-290 cm precipitation/yr) and reference streams (controls). The hypotheses were as follows: wet environments will be different from dry environments in terms of the number of colony forming units. Furthermore, it is hypothesized that wetter environments should support a greater number of CFUs and that microbial species will show preference for either wet or dry environments. Lastly, it is hypothesized that ion concentrations will be greater in wetter environments and will affect microbial growth. There was no significant relationship between the number of colony-forming units and sampling location (wet vs. dry, wet vs. reference, dry vs. reference), as determined by a Kruskal-Wallis test. No species showed a specific preference for one environment over the other. No pathogenic organisms were recovered through biochemical analyses, though opportunistic pathogens were present. 9 of the 14 organisms identified are a normal part of warm-blooded flora. Contrary to my hypothesis, and in support of Lindsey (2018), I found higher concentrations of dissolved ions at sites receiving less annual rainfall (Figures 5, 6, 7 and 8). Heavier precipitation results in dilution, while evaporation results in accumulation of ions (Lindsey 2018). This could affect microbial metabolism, as well as alter community structure as climate continues to change (Prayitno et al. 2018). This study provides a snapshot of microbial composition after precipitation events, which may broaden understanding of the affect heavy rain events have on microbes and, subsequently, human and ecosystem health.