HYDROGEOLOGY, SPRINGS, AND BIOGEOGRAPHY OF BENTHIC MACROINVERTEBRATE AND MICROBIAL COMMUNITIES. ARE THERE SIMILAR PATTERNS ACROSS A DESERT LANDSCAPE?

Study in ~40 southern Great Basin shows that geochemistry is the primary factor driving the structure of benthic macroinvertebrate and microbial communities in springs. Here we examine how extension of the region over the past 12 my resulted in a breaking a broad, mid elevation plateau into a series of north-south oriented ranges with intervening basins that may have influenced the biogeography benthic macroinvertebrate (BMI) and microbial communities. This is examined through three a posteriori hypotheses that are based on characteristics of existing hydrochemistry and in mountain, bajada, valley floor, and regional springs in an area from the Sierra Nevada east to the Spring Mountains and from the Nevada Tests Site south to the Garlock Fault. Hypothesis 1—Communities are structured by the unique geochemistry attributed to the geology of each mountain range and valley. Hypothesis 2—The diversity of the geochemistry and communities is a function of elevation and groundwater flow pathways. Hypothesis 3–The structure of communities varies relative to geochemical characteristics that can be attributed to separation of mountain ranges and newer aquatic systems in the intervening valleys which is evident by structure of communities varying along an east/west gradient in response to expansion. These are considered in context of predictions that are consistent and several that are in contrast. Statistical and multivariate analyses find the structure of BMI and microbial communities is consistent with each hypothesis. The importance of, and possible similarities in, water chemistry and the presence of many endemic crenobionts in the region suggest that contemporary communities may be relicts of similar communities present since the the late Miocene.