Berkeley Lab

Bhavna Arora speaks with News Deeply about the consequences of drought on Colorado

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Bhavna Arora (right) and former intern Madison Burrus discuss the computer simulations they are creating using data about river discharge, precipitation, and snowpack collected from the East River catchment site near Crested Butte, CO. (Credit: Marilyn Chung/Berkeley Lab)

SFA researcher Bhavna Arora was interviewed on Water Deeply regarding how declining snowpack is altering water quality in the Colorado River.

A more comprehensive interview and story were conducted by the Berkley Lab News Center, where Bhavna explains how drought and other extremes impact water pollution. Read more »

Vadose Zone Journal Special Issue features Watershed Function SFA Overview

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An overview of the Watershed function SFA and the associated East River Watershed was published in in the Vadose Zone Journal “Special Section: Hydrological Observatories”. The paper describes several recently developed approaches to interrogate, monitor and simulate transient watershed partitioning and biogeochemical responses – from genome to watershed spatial scales and from episodic to decadal timescales.

View the full paper (open access) here.

Geochemical Exports to River from the Intra-Meander Hyporheic Zone under Transient Hydrologic Conditions at East River

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Figure 1: Spatial distributions of dissolved geochemical species in groundwater in the meander C.

Hyporheic exchange within the intra-meander region results in the interaction of nutrient-rich groundwater and oxygen-rich river water, which leads to the formation of distinct redox gradients. These redox gradients can significantly impact the export of metals and nutrients at the local, reach, and watershed scales. Further, transient hydrologic conditions, such as groundwater flow dynamics, river-stage fluctuations, and rainfall/snowmelt events, can impact redox processes in the hyporheic zone and ultimately the geochemical exports to the river thereby affecting river water quality. Here we have used high-resolution hydrodynamic assessments of the hyporheic zone combined with detailed pore-water sampling to focus on the hyporheic exchange at the meander scale for the purpose of quantifying the subsurface exports from a single meander to the river under transient hydrological conditions.

This study is a first of its kind that examines the influence of transient hydrological conditions on the hyporheic biogeochemistry using field observations. Simulation results demonstrated that intra-meander hyporheic zones display distinct anoxic and suboxic regions, suboxic regions being localized along sides of the meander bend. Permeability within the meander has a more significant impact on biogeochemical zonation compared to the reaction pathways for transient hydrologic conditions. Here we have also demonstrated the outsized implications of micro-topographic features such as gullies on redox processes using the high-resolution LiDar data.

Figure 2. Net cumulative geochemical export of TIC, DOC, and iron(II) from a single meander. River-stage is shown in green on the right y-axis, whereas the net export is shown in golden color on the left y-axis.

Summary

Hyporheic zones perform important ecological functions by linking terrestrial and aquatic systems within watersheds. Hyporheic zones can act as a source or sink for various metals and nutrients. Transient hydrologic conditions alter redox conditions within an intra-meander hyporheic zone thus affecting the behavior of redox-sensitive species. Here we investigated how transient hydrological conditions control the lateral redox zonation within an intra-meander region of the East River and examined the contribution of a single meander on subsurface exports of carbon, iron, and other geochemical species to the river. The simulation results demonstrated that the reductive potential of the lateral redox zonation was controlled by groundwater velocities resulting from river-stage fluctuations, with low-water conditions promoting reducing conditions. The sensitivity analysis results showed that permeability had a more significant impact on biogeochemical zonation compared to the reaction pathways under transient hydrologic conditions. The simulation results further indicated that the meander acted as a sink for organic and inorganic carbon as well as iron during the extended baseflow and high-water conditions; however, these geochemical species were released into the river during the falling limb of the hydrograph. This study demonstrates the importance of including hydrologic transients, using a modern reactive transport approach, to quantify exports within the intra-meander hyporheic zone at the riverine scale.

Citation

Dwivedi, D., C.I. Steefel, B. Arora, M. Newcomer, J.D. Moulton, B. Dafflon, B. Faybishenko, P. Fox, P. Nico, N. Spycher, R. Carroll, and K.H. Williams (2018), Geochemical Exports to River from the Intra-Meander Hyporheic Zone under Transient Hydrologic Conditions: East River Mountainous Watershed, Colorado, Water Resources Research, 10.1029/2018WR023377.

First Watershed Science Collaboration Workshop takes place Sep 23-25, 2018 in Crested Butte, CO

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The workshop began with a guided tour of the East River watershed.

Attendees pose briefly for a group photo.

Attendees included microbial and plant ecologists, hydrologists, geochemists, geologists, geophysicists, remote and snow sensing experts, data and computational scientists and resource managers. Read more »

Using strontium isotopes to evaluate how local topography affects groundwater recharge

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Figure 1. 87Sr/86Sr vs 1/[Sr] showing the mixing relationships between vadose zone porewater and groundwater. Blue line shows the mixing model of vadose zone water with upgradient groundwater with bold numbers representing the percentage of vadose zone water in the local aquifer.

A key component of understanding the connection between groundwater quality and the vadose zone (the water unsaturated region above the water table) is the movement of water from the surface to the aquifer (recharge). Measurements of the natural isotopic composition of Sr were used to assess the effect of local topography on groundwater recharge across a semi-dry riparian floodplain in the Upper Colorado River Basin.

This work demonstrates the use of 87Sr/86Sr (Sr isotopes) to measure groundwater recharge through analysis of porewater and groundwater samples from the vadose zone. The study resulted in an understanding how the microtopography of the Rifle Site affects the hyper-local variation in the downward movement of vadose-zone porewater that may carry nutrients and contaminants to groundwater.

Figure 2. “Heat” map of the percentage contribution of vadose water to the Rifle floodplain aquifer based on the Sr isotopic mixing model.

Summary

Over time, loose sand, clay, silt, gravel or similar unconsolidated, or “alluvial” material is deposited by water into alluvial aquifers. Recharge of alluvial aquifers is a key component in understanding the interaction between floodplain vadose zone biogeochemistry and groundwater quality. The Rifle Site (a former U-mill tailings site) adjacent to the Colorado River is a well-established field laboratory that has been used for over a decade for the study of biogeochemical processes in the vadose zone and aquifer. This site is exemplary of both a riparian floodplain in a semiarid region and a post-remediation U-tailings site. The authors use Sr isotopic data for groundwater and vadose zone porewater samples to build a mixing model for the fractional contribution of vadose zone porewater (i.e. recharge) to the aquifer and to assess its distribution across the site. The vadose zone porewater contribution to the aquifer ranged systematically from 0% to 38% and appears to be controlled largely by the microtopography of the site. The area-weighted average contribution across the site was 8%, corresponding to a net recharge of 7.5 cm. Given a groundwater transport time across the site of ~1.5 to 3 years, this translates to a recharge rate between 5 and 2.5 cm/yr, and with the average precipitation to the site, implies a loss from the vadose zone due to evapotranspiration of 83% to 92%.

Citation

Christensen, J. N., et al. (2018), Using strontium isotopes to evaluate the spatial variation of groundwater recharge, Sci Total Environ, 637-638, 672-685, DOI: 10.1016/j.scitotenv.2018.05.019.

September 2018 updates

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We have several upcoming items that are worthy of special mention, as they’re broadly relevant to our group and the larger community of RMBL researchers and our growing community of interagency (DOE, USGS, NSF, USFS, NOAA, NASA, etc.) partners. Details and points of contact below.

NASA JPL Airborne Snow Observatory (ASO):

The NASA JPL ASO team conducted their snow-free survey of the Upper Gunnison domain last week, including essentially all of the terrain above the Ohio Creek/Gunnison River confluence. These data will enable retrospective snow depth and SWE mapping from the April 1 and May 24, 2018 flights this past spring, and set the stage for near-real time snow mapping in winter and spring 2019. This is a huge deal and incredibly important as we engage our collaborators with NCAR and NOAA on further developing a snow-focused computational testbed in the upper Gunnison.

Recall that this activity has been made possible through the vigorous engagement of the Upper Gunnison Water Conservancy District (thank you Frank and John) and with funding from the State of Colorado and champions at the Colorado Water Conservation Board (thank you Joe).

Also a reminder that this work is critically important to two of the three newly funded DOE SBR University snow science proposals at East River: Jeff Deems (CU) and McKenzie Skiles (Univ. Utah). So great news that this snow free-baseline dataset is now in hand.

NASA SnowEx:

I am excited to announce that the NASA SnowEx campaign will be active in the broader East River / Watershed Function SFA domain this winter and spring (2018/19). NASA SnowEx is coupled multi-year remote sensing and field experiment to develop and refine techniques for mapping terrestrial snow cover around the globe to address important water resources, water cycle, and climate feedback challenges. In 2017, SnowEx conducted intensive, month-long campaigns on Grand Mesa and in Senator Beck Basin in western Colorado. In 2019, SnowEx will leverage ongoing and planned observation activities around the western US to collect time series data of snowpack evolution throughout the accumulation and melt seasons in a diversity of snow climates at sites in CA, ID, UT, CO, and NM.

In the East River domain specifically, the SnowEx campaign will build on planned ASO flights (funded by the Colorado Water Conservation Board) and the aforementioned recently-funded DOE snow observation and modeling projects (see above; Deems, Skiles, Alejandro Flores [Boise State] PIs) and NSF (Raleigh [CU]), with the broader Watershed SFA activities adding valuable synergies. Additional ASO winter flights are being planned, as well as twice-monthly UAVSAR (L-band interferometer) overflights. These airborne acquisitions will be supported by regular ground observations and periodic extensive field campaigns to sample gradients in snow properties and processes.

At the risk of underselling this — this is a huge deal. Please contact Jeff Deems (deems@nsidc.org) with any questions!

Upcoming drilling activities:

Building upon our very successful drilling projects with USGS in Redwell Basin, we are planning to drill a collection of deep shale wells starting in early October to provide ground-truthing for both surface and airborne geophysical data collection. Drilling of four monitoring boreholes (40-70m deep) will occur to (a) recover shale bedrock for geochemical analysis and (b) provide long term sampling ports for evaluating seasonal changes in groundwater elevation and chemistry.

Equally as important to geological constraints, we’re pursuing a drilling campaign that folds in other extant RMBL researchers from the perspective of biogeochemistry.

As an NC State postdoc, Amanda DelVecchia (amanda.delvecchia@gmail.com) — in order to study geologic methane contributions to contemporary food webs — will be installing five 2″ diameter, 2 mm slotted PVC wells to bedrock on the lower East River (our “Pumphouse” location) using a Geoprobe this October. As part of this work, Amanda will be collecting methane samples from these wells and others for submission to collaborator Dr. Daniel Stolper (UC Berkeley) for analysis of clumped isotopologues.

So we have a busy October in front of us insofar as drilling is concerned!

Lastly — and this is purely for the geology and geocentric folks on this list — I wanted to provide a link to a remarkable document. It fleshes out Ferdinand Hayden’s original geologic surveys for the state of Colorado including the East River watershed from the late 1800’s.

Building upon the shoulders of giants is what we do — and with Hayden laying the geologic framework for Yellowstone, I’d say he qualifies — I’m including the link below.

https://haydenslandscapes.com/part-iii-elks-and-west-elks/east-river-gothic

This is so well done and with a focus on the East River and its environs from the late 1800’s, it’s hard to overvalue it.

Unexpected High Carbon Fluxes from the Deep Unsaturated Zone in a Semi-Arid Region

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Figure: Estimated carbon fluxes and balance along the measurement transect, showing 30% of annual CO2 emissions from deeper than 1.0 m, contrary to predictions of < 1% by the Earth System Models.

Understanding of terrestrial carbon cycling has relied primarily on studies of top soils that are typically characterized to depths shallower than 0.5 m. We found and quantified 30% of CO2 annual efflux to atmosphere (60% in winter) originates from below 1 m, contrary to prediction of <1% by the ESM land models.

We contend that ESM land models need to incorporate these deeper soil processes to improve CO2 flux predictions in semi-arid climate regions.

Summary

Understanding of terrestrial carbon cycling has relied primarily on studies of topsoils that are typically characterized to depths shallower than 0.5 m. At a semi-arid site, instrumented down to 7 meters, we measured seasonal- and depth-resolved carbon inventories and fluxes, and groundwater and unsaturated zone flow rates. We identified an unexpected high dissolved organic carbon (DOC) flux from the rhizosphere into the underlying unsaturated zone. We measured that ~30% of the CO2 efflux to atmosphere (60% in winter) originates from below 1 m, contrary to prediction of <1% by Earth System Model land models. The seasonal DOC influx and favorable temperatures, moisture and oxygen availability in deeper unsaturated zone sustained the respirations of deeper microbial communities and roots. These conditions are common characteristics of many subsurface environments; thus we contend that ESM land models need to incorporate these deeper soil processes to improve CO2 flux predictions in semi-arid climate regions.

Citation

Wan, J., Tokunaga, T.K., Dong, W., Williams, K.H., Kim, Y., Conrad, M.E., Bill, M., Riley, W.J., Susan S.H., Deep unsaturated zone contributions to carbon cycling in semiarid environments. Journal of Geophysical Research: Biogeosciences, 123. https://doi.org/10.1029/2018JG004669.

Factors Controlling Seasonal Groundwater and Solute Flux from Snow-Dominated Basins

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Fig. 1: Mixing diagram in U-space with Pumphouse stream discharge plotted in rainbow. Seasonal end-member means are connected with grey connecting lines while end-member variability (black error bars) determined using ±1sd of observed tracer concentrations.

Research identifies critical zone influences on hydrologic partitioning and tracer variability as reflected in seasonal stream concentration-discharge (C-Q) relationships. The method is applied across scale and within topographically complex, snow-dominated basins. First-order controls on seasonal streamflow generation are isolated and hydro-chemical conceptual model development is initiated.

The role of groundwater contribution to snow-dominated, low-order streams residing in basins of large relief is found significant; with recharge increasing in the upper sub-alpine where maximum snow accumulation is coincident with reduced conifer cover and lower canopy densities. Error in estimated stream concentrations is attributed to differences in water partitioning, source rock, seasonal shifts in flow path and sulfate reduction in floodplain sediments.

Fig. 2: Topographic and vegetation controls on snow water equivalent (SWE) and fraction of streamflow that is groundwater (fGW).

Summary

To isolate first-order controls on seasonal streamflow generation within highly heterogeneous, snow-dominated basins of the Colorado River, authors developed a multivariate statistical approach of end-member mixing analysis (EMMA) using a suite of daily chemical and isotopic observations. Mixing models are developed across 11 nested basins (0.4 km2 to 85 km2) spanning a gradient of climatological, physical and geological characteristics. Hydrograph separation using rain, snow and groundwater as end-members indicates that seasonal contributions of groundwater to streams is significant. Mean annual groundwater flux ranges from 12% to 33% while maximum groundwater contributions of 17% to 50% occur during baseflow. Groundwater recharge is found to increase in basins of high relief and within the upper sub-alpine where maximum snow accumulation is coincident with reduced conifer cover and lower canopy densities (Fig. 1). The mixing model developed for the furthest downstream site did not transfer to upstream basins. The resulting error in predicted stream concentrations points toward weathering reactions as a function of source rock and seasonal shifts in flow path. Additionally, the potential for microbial sulfate reduction in floodplain sediments along a low gradient, meandering portion of the river is sufficient to modify hillslope contributions and alter mixing ratios in the analysis. Soil flushing in response to snowmelt is not included as an end-member but is identified as an important mechanism for release of solutes from these mountainous watersheds.

Citation

R. W. H. Carroll, L. A. Bearup, W. Brown, W. Dong, M. Bill, and K. H. Williams, “Factors Controlling Seasonal Groundwater and Solute Flux from Snow-Dominated Basins.” Hydrological Processes, Special Issue: Water in the Critical Zone 32 (14), 2187-2202 (2018). [https://doi.org/10.1002/hyp.13151].

An early warning system for tracking groundwater contamination

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Figure 1. Kalman-filter based in situ real-time monitoring system

A real-time, in-situ, ‘smart’ monitoring and early warning system for migrating and reacting contaminant plumes was developed using a Kalman filter-based framework and successfully tested at the contaminated Savannah River Site.

Figure 2. System validation using historical, cheap proxy variables (specific conductance and pH) to estimate U-238


As this framework enables easy integration of networked, autonomous and inexpensive wellbore measurements with cloud computing, the approach is expected to reduce groundwater monitoring cost, increase confidence in the efficacy of monitored natural attenuation, and ensure early response if needed.

Summary
  • A Kalman filter method was used to estimate contaminant concentrations continuously and in real-time by coupling data-driven concentration decay models with data correlations.
  • The approach was successfully demonstrated using historical groundwater data from the Uranium and Tritium-contaminated Savannah River Site F-Area
  • Specific conductance and pH were used as proxy variables to estimate tritium and uranium concentrations over time.
  • Results show that the developed method can estimate contaminant concentrations based on in-situ, easily measured variables
Citation

Schmidt, F., Wainwright, H. M., Faybishenko, B., Denham, M., & Eddy-Dilek, C. (2018). In Situ Monitoring of Groundwater Contamination Using the Kalman Filter. Environmental Science & Technology, DOI: 10.1021/acs.est.8b00017.

August 2018 – Field update and new “Meet the Scientist” videos

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(A) We successfully completed the drilling of the second deep well (150-ft below grade) in Redwell Basin. As noted previously, we encountered artesian flow at 150-ft, which brought an end to further downward progress. Prior to open hole geophysical logging and well completion, Mike Wilkins (Colorado State Univ.), joined me to collect a “deep microbiome” filtered sample for metagenomics analysis. We were able to serially filter (1.2, 0.2, 0.1-um) ca. 26-L of groundwater from the artesian flow zone at 150-feet within a metal sulfide-rich portion of the formation. These filters are currently stored at -80C in Gothic and will be sent to Jill Banfield (UC Berkeley) once preparations are made. Mike and I discussed the possibility for temporal omic-sampling from this depth if completion strategies being pursued this week result in sampling infrastructure that will allow for it. Fingers crossed for that.

(B) We’ve had an extremely active two weeks of field work. In the field have been teams led by Audrey Sawyer (Ohio State) and Mike Wilkins (CSU) working at Pumphouse on hyporheic zone biogeochemistry, Marty Briggs (USGS) et al. investigating a diversity of surface water-groundwater interaction zones using UAV imaging and fluorescence tracer injections, and John Bargar (SLAC) whose SLAC SFA team continues to probe heavy metal accumulation in floodplain sediments and redox-mediated processes impacting its fate along the Slate River / Oh-Be-Joyful confluence zone.

(C) While I’ve previously introduced John and his project to the team, I did want to introduce folks to the work of Audrey and Mike at Pumphouse and Marty et al. at Oh-Be-Joyful (and beyond). These “Meet the Scientist” videos run their usual ca. 3-min length, and I hope you’ll take the chance to watch them to find out what your East River collaborators are up to of late.

(D) Lastly — and as I say hopefully without irony — it’s all over but for the crying at Old Rifle. While I still maintain a small but active research footprint there examining uranium remediation via hydroxyapatite formation, we’ve reached a critical inflection point for that site. The attached photos tell the story, and for that group of dedicated “Old Rifle” readers, you might better find a box of tissue. I can safely say that Old Rifle made my career and that of so many others on and off this email list. We created what is without question the world’s foremost subsurface microbial observatory and we — especially DOE-SC and DOE-LM — should be rightfully proud. To plagiarize from Friday Night Lights: “Rifle forever.”