Floodplains vs. hillslopes: Informing the timing and tempo of clay formation and organic matter stabilization across an alpine watershed

Soils store substantial amounts of carbon as organic matter. However, the size of this C reservoir

reservoir

A manmade lake that is created when a dam is built on a river. River water backs up behind the dam creating a reservoir.

Source: USGS Source

may be sensitive to climatic change motivating research on the mechanisms governing soil organic matter stabilization. One existing paradigm for organic matter stabilization suggests that the phyllosilicate “clay” minerals that form in soils protect organic matter from breakdown. However, models are not capable of fully representing this process pointing to knowledge gaps regarding the interactions between organic matter and minerals, their constitutive controls, and their timescales of operation. More broadly, there are persistent challenges in describing the co-evolution of soil mineralogy, structure, and organic matter storage, which limits the treatment of soil dynamics in Earth systems models and their concomitant effects on future climate projections.

Here, we propose to advance our understanding of how clay minerals and organic matter interact at the terrestrial-aquatic interface using the East River watershed

watershed

An area of land that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually flows to the lowest point in a basin.

Source: USGS Source

as a natural laboratory. In addition to traditional methods, measurements of stable lithium isotopic ratios, which is one of the foremost proxies for quantitatively gauging clay mineral formation, will be central to the proposal. Critically, our approach will enable the detection of “hot spots” and “hot moments” of clay mineral formation by studying different landscape elements (e.g., floodplain

floodplain

The nearly flat portion of a river valley built by sediment deposited during previous floods.

Source: NASA earth observatory Source

vs. hillslope), components of the hydrosphere (e.g., groundwater

groundwater

Water that occurs below Earth's surface. When rain falls to the ground, a portion percolates (sinks) into the ground and collects in spaces in the underground rocks.

Source: A student's guide to Global Climate Change Source

vs. surface water)

surface water

Any body of water above ground, including streams, rivers, and lakes.

Source: NASA Source

, and timescales of biogeochemical cycling (e.g., rainfall events, the seasonal cycle, and landscape evolution over millennia). Ultimately, these measurements will be used to improve models that relate field and laboratory measurements with Critical Zone processes.

The East River watershed represents an ideal locality to interrogate these questions because of the extensive study that has already characterized it, a large sample archive, and existing sampling infrastructure that permits geochemical analyses at high spatial and temporal frequencies. Given the outsized role of headwater ecosystems

ecosystem

A natural community of plants, animals, and other living organisms and the physical environment in which they live and interact.

Source: A student's guide to Global Climate Change Source

in terrestrial

terrestrial

The geographical and biological features that are associated with the Earth's solid, rocky surface, residing on or resembling the land or terrain found on our planet.

Source: NASA Source

biogeochemical cycles, the proposed work will build a theoretical and methodological framework for soil formation and organic matter stabilization that is applicable to other watersheds and will lead to a more accurate depiction of terrestrial carbon cycling in Earth system models.

earth system model (ESM)

A model that simulates how chemistry, biology, and physical forces work together. These models are similar to, but much more comprehensive than, global climate models.

Source: U.S. Department of Energy Source

Lastly and importantly, the project will include the training of 1 graduate student and postdoctoral researcher in laboratory and computational methods.