Interactions Between Microbial Communities and Landscape Evolution in Eastern Sierra Nevada, CA ( EP43E-2470)
Welcome to the detailed version of my AGU poster!
Here you'll find more in-depth information about the research and findings featured in the poster.
For more information or inquiries, please feel free to reach out.
Thank you for your interest.
Earth's critical zone. Illustration by Critical Zone Observatories (CZO) based on a figure in Chorover et al. 2007.
Biological weathering
•Weathering is the first step in landscape evolution. The physical and chemical disintegration of rocks and minerals to solutes and particulate matter.
•Weathering agents can be divided into macro (plants and animals) and micro (bacteria, fungi, and others).
•Microbial weathering mostly happens in soils - Soils are one of the most microbially diverse environments on Earth.
"In every cubic centimeter of soil, there are billions of microbes, most of which are unknown to science.“
David Suzuki
Microbial weathering
There are diverse weathering mechanisms used by microbes
We can divide these contributions:
* Direct weathering – chemical or physical weathering
Indirect weathering – changes to soil pH and symbiotic relationships (supporting other weathering-inducing organisms)
The more diverse a microbial community the more weathering pathways.
SEM images of pyrite grains after abiotic incubation (left) and incubation with pyrite-oxidizing microbes (right).
From Napieralski et al. (2021)
Clear discrete Fe oxide nanocrystals in the abiotic systems.
Landscape on Mars taken by NASA's Curiosity rover
The big questions
What is the role that microbially mediated weathering plays in long-term large-scale surface processes?
How do microbial communities develop and change during the transformation from rock to soil and over the timescales of soil development?
schematic diagram
Replacing space for time: working in recently deglaciated landscapes
During deglaciations as glaciers shrink and retreat, they expose fresh rock with no soils.
Sampling in a recently deglaciated basin should produce a time transect with elevation (closer to the glacier = younger)
MODIS image of snow-covered mountains in California. Blue dots are mapped snow or ice bodies from Fountain et al. (2007)
Sabrina Lake Basin, Bishop Creek, CA
Field site
The Sierra Nevada mountain range was heavily glaciated during the Pleistocene.
Presently, ∼1700 small glaciers and small ice masses occupy sheltered cirques near the crest of the range occurring above 3250 m in elevation
Sampling in the eastern Sierra Nevada
Collecting samples along an elevational transect from ~2800 m to ~3200 m.
We collected surface rock samples and soil and saprolite samples from adjacent sampling locations (<2 m apart)
Exposure ages and weathering rates
Cosmogenic 10Be surface exposure ages agree with 14C ages from organic material in a Baboon Lake
No clear change in exposure ages along the transect
Rates of surface processes
Rapid deglaciation in Sabrina Lake basin ~13 ka correlating to the Recess Peak glaciation
Fast weathering rates with some variability between the sites
Weathering rates do not correlate with elevation
Rapid long-term weathering across the basin points to an active landscape
Microbial ecology in Sabrina Lake
DNA sequencing (16S rRNA) of soil, saprolite, and surface rock samples
“Census of bacteria” – determining the different microbial species in the samples are their abundances
Microbial community composition
Bar chart of taxonomic profiles of bacterial community at phylum level with abundance >1%
Similarity in microbial community composition between soils and saprolites & a clear difference in the rock microbial community (geochemically, saprolite and rock are very similar)
More diversity in soil and saprolite samples
Microbial community diversity
Shannon’s Diversity is a way to measure the diversity of species in a community (based on the number of species and their relative abundance)
Surface rock microbial communities are less diverse than soil and saprolite communities
Possible change with elevation…
Microbial community diversity
No clear link between chemical weathering rates and microbial community diversity along the sites…
Diversity and uniqueness of different habitats
Venn diagram of AVS by sample type.
Rock samples are significantly less diverse than soil and saprolite.
While there is some overlap between soil and saprolite, the microbial communities in rock samples are mostly unique.
Habitat controlling microbial communities
Nonmetric multidimensional scaling (NMDS) analyses shows that the main control on the composition of microbial communities is the habitat (sample type).
Changes in elevation do not appear to impact microbial community composition
Microbial habitats and environmental roles
Microbial community composition heatmap of the different biological habitats. Rock species feature more
extremophiles and primary colonizers species, while soil and saprolite samples contain a more diverse
range of chemoheterotrophic species, nitrogen fixators, and hydrocarbon degraders.