Geology topics

Jon Chorover

Publications and source records attributed to Jon Chorover.

6 recordsLinked to original sources

USGS2025

Groundwater dominates snowmelt runoff and controls streamflow efficiency in the western United States

Climate change in seasonally snow-covered mountain catchments is reducing water supply and decreasing streamflow predictability. Here, we use tritium age dating to show that contrary to the common assumption that snowmelt quickly contributes to runoff, streamflow during snowmelt in western US catchments is dominated by older groundwater. The average age of streamwater during snowmelt runoff (5.7 ± 4.3 years) was intermediate to the average age of groundwater (10.4 ± 4.5 years) and recent precipitation, indicating that 58% (±34%) of snowmelt runoff was derived from groundwater. Water ages, streamflow, and groundwater storage were mediated by bedrock geology: low-permeability hard rock/shale catchments exhibited younger ages, less storage, and more efficient streamflow generation than high-permeability sandstone/clastic catchments. Our results demonstrate that snowmelt runoff is the result of multiple prior years of climate mediated by groundwater storage. Including these interactions will be crucial for predicting water resources as climate and landscape changes accelerate.

western united States↗

USGS2021

Signatures of hydrologic function across the critical zone observatory network

Despite a multitude of small catchment studies, we lack a deep understanding of how variations in critical zone architecture lead to variations in hydrologic states and fluxes. This study characterizes hydrologic dynamics of 15 catchments of the U.S. Critical Zone Observatory (CZO) network where we hypothesized that our understanding of subsurface structure would illuminate patterns of hydrologic partitioning. The CZOs collect data sets that characterize the physical, chemical, and biological architecture of the subsurface, while also monitoring hydrologic fluxes such as streamflow, precipitation, and evapotranspiration. For the first time, we collate time series of hydrologic variables across the CZO network and begin the process of examining hydrologic signatures across sites. We find that catchments with low baseflow indices and high runoff sensitivity to storage receive most of their precipitation as rain and contain clay‐rich regolith profiles, prominent argillic horizons, and/or anthropogenic modifications. In contrast, sites with high baseflow indices and low runoff sensitivity to storage receive the majority of precipitation as snow and have more permeable regolith profiles. The seasonal variability of water balance components is a key control on the dynamic range of hydraulically connected water in the critical zone. These findings lead us to posit that water balance partitioning and streamflow hydraulics are linked through the coevolution of critical zone architecture but that much work remains to parse these controls out quantitatively.

Water Resources Research↗

USGS2017

CO2 diffusion into pore spaces limits weathering rate of an experimental basalt landscape

Basalt weathering is a key control over the global carbon cycle, though in situ measurements of carbon cycling are lacking. In an experimental, vegetation-free hillslope containing 330 m 3 of ground basalt scoria, we measured real-time inorganic carbon dynamics within the porous media and seepage flow. The hillslope carbon flux (0.6–5.1 mg C m –2 h –1 ) matched weathering rates of natural basalt landscapes (0.4–8.8 mg C m –2 h –1 ) despite lacking the expected field-based impediments to weathering. After rainfall, a decrease in CO 2 concentration ([CO 2 ]) in pore spaces into solution suggested rapid carbon sequestration but slow reactant supply. Persistent low soil [CO 2 ] implied that diffusion limited CO 2 supply, while when sufficiently dry, reaction product concentrations limited further weathering. Strong influence of diffusion could cause spatial heterogeneity of weathering even in natural settings, implying that modeling studies need to include variable soil [CO 2 ] to improve carbon cycling estimates associated with potential carbon sequestration methods.

Geology↗

USGS2015

The Landscape Evolution Observatory: a large-scale controllable infrastructure to study coupled Earth-surface processes

Zero-order drainage basins, and their constituent hillslopes, are the fundamental geomorphic unit comprising much of Earth's uplands. The convergent topography of these landscapes generates spatially variable substrate and moisture content, facilitating biological diversity and influencing how the landscape filters precipitation and sequesters atmospheric carbon dioxide. In light of these significant ecosystem services, refining our understanding of how these functions are affected by landscape evolution, weather variability, and long-term climate change is imperative. In this paper we introduce the Landscape Evolution Observatory (LEO): a large-scale controllable infrastructure consisting of three replicated artificial landscapes (each 330 m 2 surface area) within the climate-controlled Biosphere 2 facility in Arizona, USA. At LEO, experimental manipulation of rainfall, air temperature, relative humidity, and wind speed are possible at unprecedented scale. The Landscape Evolution Observatory was designed as a community resource to advance understanding of how topography, physical and chemical properties of soil, and biological communities coevolve, and how this coevolution affects water, carbon, and energy cycles at multiple spatial scales. With well-defined boundary conditions and an extensive network of sensors and samplers, LEO enables an iterative scientific approach that includes numerical model development and virtual experimentation, physical experimentation, data analysis, and model refinement. We plan to engage the broader scientific community through public dissemination of data from LEO, collaborative experimental design, and community-based model development.

Arizona↗

USGS2011

Proposed initiative would study Earth's weathering engine

At the Earth's surface, a complex suite of chemical, biological, and physical processes combines to create the engine that transforms bedrock into soil (Figure 1). Earth's weathering engine provides nutrients to nourish ecosystems and human society mediates the transport of toxic components within the biosphere, creates water flow paths that carve and weaken bedrock, and contributes to the evolution of landscapes at all temporal and spatial scales. At the longest time scales, the weathering engine sequesters CO 2 , thereby influencing long-term climate change. Despite the importance of soil, our knowledge of the rate of soil formation is limited because the weathering zone forms a complex, ever-changing interface, and because scientific approaches and funding paradigms have not promoted integrated research agendas to investigate such complex interactions. No national initiative has promoted a systems approach to investigation of weathering science across the broad array of geology, soil science, ecology and hydrology. Such a program is certainly needed, and this article describes a platform on which to build the initiative to answer the following question: How does the Earth weathering engine break down rock to nourish ecosystems, carve terrestrial landscapes, and control carbon dioxide in the global atmosphere?

Eos Science News↗

USGS2010

Comparison of transport and attachment behaviors of Cryptosporidium parvum oocysts and oocyst-sized microspheres being advected through three minerologically different granular porous media

In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43–46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22–29% by mass), aluminum (29–45% by mass), and clay-rich (68–76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed for the red, metal-oxide rich soil from Oahu. In contrast, colloidal attachment in the organic-rich, volcanic ash soil was relatively insensitive to changes in pH in spite of the high iron content. Given the fundamental differences in transport behavior of oocyst-sized colloids within the two volcanic soils of similar origin, agricultural practices modified to lessen C. parvum contamination of ground or surface water would necessitate taking the individual soil properties into account.

Water Research↗