EXAMINING LANDSCAPE PLACEMENT AS A CONTROL ON SPRING HYDROCHEMISTRY AND ECOLOGICAL DIVERSITY

Springs are the primary hydrologic features supporting desert and montane aquatic ecosystems in the southern Great Basin (US). This region is notable for its extreme temperature variability, dramatic relief, numerous desert ecotones, and complex geology. Preliminarily interdisciplinary work on spring ecosystems incorporating hydrogeology, aqueous geochemistry, microbiology, and aquatic ecology indicates that relative topographic position or landscape placement (i.e., mountain, bajada, valley floor, playa, regional) is an indicator of benthic ecological community diversity in undisturbed springs. For example, mountain springs typically have benthic macroinvertebrate populations with higher diversity than playa or regional springs. At smaller scales, we find that microbial community diversity strongly correlates with spring elevation across the southern Great Basin. These macro and micro ecological relationships with landscape placement are partially a function of spring physicochemical metrics like discharge temperature and salinity. These metrics are important for defining ecological tolerance thresholds and have regional and local relationships with relative topographic position. Here we investigate the inherent relationships between spring landscape placement, elevation, simple geochemical metrics, and isotopic markers at regional and mountain block scales across the rain shadow of the southern Sierra Nevada. We leverage the vast amount of existing work on springs in the region to compile a geochemical database and then supplement this collection with the results of recent sampling efforts (2016-2019). Our results suggest that while spring landscape placement exerts some control on geochemical and isotopic metrics at local and regional scales, tectonic and geologic controls like the emergence mechanism (i.e., major regional fault, localized normal faulting, geologic contact, topographic) are also important. Both landscape position and the driver of spring emergence may be important criteria that will ultimately help describe how these desert springs will respond to the effects of climate change.