Relationships Between Aquatic Ecology, Landscapes, Hydrogeology and Hydrochemistry in Great Basin and Mojave Desert Spring Systems USA

Abstract

Springs are groundwater-dependent systems sustaining most of the riparian and aquatic habitat in western North America's deserts. The relationship between hydrogeology and springs is recognized by groundwater hydrologists and ecologists; however, studies integrating these disciplines have focused on site and species-specific relationships. We examined environmental and biotic characteristics of persistent, reference springs following a Modified Regional Hydrologic Framework in 53 Great Basin and Mojave Desert springs. Springs in this region are fed by groundwater flow from various aquifers and they vary widely in elevation, discharge, substrate composition, temperature and electrical conductance (EC). Structural and bioassessment metrics of benthic macroinvertebrate communities were strongly associated with aquifer type (provenance) landscape settings, and groundwater flow paths (and associated residence times). Characteristics of these communities generally varied along an environmental gradient with intolerant communities in mountain aquifer springs, where groundwater flow paths and residence times are short, water is cool and EC is low. Increasingly tolerant communities occupy local aquifer bajada, local aquifer valley floor, (alluvial valley and playa) and local aquifer geothermal springs; and regional aquifer springs; where groundwater flow paths and residence times are longer than mountain aquifer springs, water is warmer and EC is higher. Longer flow paths and residence times often create a variety of harsh hydrochemical conditions. Suites of crenobionts characterize regional aquifer springs, where groundwater flow paths are longest, and groundwater residence times are oldest. The importance of hydrochemistry to structuring BMI communities suggests that water chemistry provides the foundation for the basic requirements, and limitations, for taxa to exist in a spring system. From this basic set of parameters, communities are then influenced by dispersal, history and physical characteristics of spring habitats. The hydrochemical relationships among springs in this region indicate that hydrogeology and spring ecosystem ecology are closely linked in these western deserts, and that integrating ecological and hydrogeological models will enhance the efficacy of groundwater use, spring ecosystem and biodiversity management, monitoring and protection.