| Understanding patterns of bacterial community diversity and composition associated with environmental gradients is crucial to better understand the processes underlying bacterial biogeography and potentially formulate predictions of how bacterial communities might respond to changing environmental conditions. It is clear that we are beginning to understand some of the patterns of bacterial diversity across space and time; however, a strong need exists for further characterizing bacterial communities across ecologically important gradients, such as depleted oxygen concentrations in aquatic ecosystems. Low oxygen zones continue to rapidly expand globally threatening ecologically and economically important aquatic habitats and the organisms within. Though upper trophic level organisms are excluded from these low oxygen environments, microbes continue to thrive and cycle energy and nutrients. Thus, understanding the changes in bacterial communities associated with gradients of environmental factors in low-oxygen zones is crucial to be able to predict and potentially rehabilitate these deteriorating ecosystems. In Chapter One, I examine changes in bacterial communities in Hood Canal, WA, which is an ideal natural laboratory to examine how bacterial communities shift across space, time, and environmental gradients. Particularly, I discuss the relationship between changes in bacterial communities with decreasing dissolved oxygen, which is a point of concern in Hood Canal where hypoxia conditions commonly occur. Appendix A contains an expansion on the selection of similarity indices used to describe patterns of bacterial community composition. Multiple biases exist in quantifying differences in bacterial community composition, and, in Appendix A, I examine the impact of these biases on numerous commonly used community similarity indices. |
