Integrated Earth Systems in the eastern Sierra Nevada, CA: Connections between mineralogy, hydrogeology, geochemistry, and benthic ecology
Abstract
The interplay among terrestrial earth systems (e.g., physical, chemical, and biotic dimensions) remains poorly quantified. It is important to identify the connections between disciplines that are often studied separately in order to understand feedback processes and the true complexity of natural systems. As hydrologic features, springs typify this interplay as they: 1) emerge and persist on the landscape as a function of geology, tectonics, and climate, 2) support surface water features but are themselves groundwater and inherit its stability, 3) discharge geochemical fluxes that reflect subsurface weathering processes, 4) and host unique ecological communities, especially in arid regions.
Here we present interdisciplinary research on cold spring ecosystems emerging along the mountain front of the eastern Sierra Nevada, some of which are directly connected to the Owens River system. We identify probable spring contributing areas using strontium isotopes, noble gas recharge elevations, stable isotopes of spring waters, and geologic cross sections. Inverse geochemical models combined with environmental tracers show that spring geochemistry is controlled by the geologic heterogeneity of the batholith and groundwater residence time. Four distinct geochemical groups are identified based on rock-water interaction: 1) springs with a granitic weathering signature typical of Sierra Nevada plutonic rocks, 2) springs with a volcanic rock weathering signature, 3) springs interacting with basinal brines and/or soluble alluvial material, and 4) springs reflecting a mixture of metasedimentary roof pendant and granitoid dissolution. Benthic macroinvertebrates (BMI), known to be sensitive to environmental physicochemical characteristics, were sampled in the same springs. We find that BMI community structure is dictated by the spring geochemistry. Intolerant species were found in the colder, low TDS springs sourcing Group 4 waters, while species hosting more intolerant organisms were found in Group 1 and Group 2 waters. Preliminarily, we also find that certain benthic microbial taxa are highly correlated to these geochemical and BMI clusters. Our work shows a direct connection between aquifer mineralogy, groundwater flowpaths, aqueous geochemistry, and aquatic BMI and microbial communities.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H44C..06M
- Keywords:
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- 0408 Benthic processes;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 1813 Eco-hydrology;
- HYDROLOGY;
- 1829 Groundwater hydrology;
- HYDROLOGY