Scientific Focus Area
Research from the Watershed Function SFA will be featured in approximately 25 posters, talks and convened sessions at the 2017 American Geophysical Union Fall Meeting in New Orleans, LA.
Click here to see a full listing of SFA-related AGU 2017 activities.
FTIR analysis (top) and pictures (bottom) of three natural organic matter fractions extracted from sediment: water extractable (MQ-SPE), acid-soluble pyrophosphate (PP) extractable (PP-SPE), and acid-insoluble PP extractable (PP >1 kD).
Organic carbon concentrations in sediments more than 1 meter below the land surface are typically 10 to 200 times lower than in surface soils, posing a distinct challenge for characterization. In this SFA study, published in Organic Chemistry, a range of chemical extractions were evaluated for extraction of natural organic matter (NOM) from low-carbon (<0.2%) alluvial sediments and an extraction and purification scheme was developed in order to isolate and characterize different fractions of sediment-associated NOM.
Surface soils typically contain 5-10% levels of organic carbon (OC), but OC concentrations in sediments more than 1 meter below the land surface are often 10 to 200 times lower, and the usual techniques to measure the chemical characteristics of OC in these sediments are not sufficiently sensitive. In this study, a range of chemical extractions were evaluated for extraction of natural organic matter (NOM) from two low-carbon (<0.2%) alluvial sediments. The OC extraction efficiency followed the order pyrophosphate (PP)>NaOH>HCl, hydroxylamine hydrochloride>dithionite, water. A NOM extraction and purification scheme was developed using sequential extraction with water (MQ) and sodium pyrophosphate at pH 10 (PP), combined with purification by dialysis and solid phase extraction in order to isolate different fractions of sediment-associated NOM. Characterization of these pools of NOM for metal content and by Fourier transform infrared spectroscopy (FITR) showed that the water soluble fraction (MQ-SPE) had a higher fraction of aliphatic and carboxylic groups, while the PP-extractable NOM (PP-SPE and PP >1kD) had higher fractions of C=C groups and higher residual metals. This trend from aliphatic to more aromatic is also supported by the specific UV absorbance at 254 nm (SUVA254) (3.5 vs 5.4 for MQ-SPE and PP-SPE, respectively) and electrospray ionization Fourier transform ion cyclotron resonance spectrometry (ESI-FTICR-MS) data which showed a greater abundance of peaks in the low O/C and high H/C region (0-0.4 O/C, 0.8-2.0 H/C) for the MQ-SPE fraction of NOM. Radiocarbon measurements yielded standard radiocarbon ages of 1020, 3095, and 9360 years BP for PP-SPE, PP >1kD, and residual (non-extractable) OC fractions, indicating an increase in NOM stability correlated with greater metal complexation, apparent molecular weight, and aromaticity.
P.M. Fox, P.S. Nico, M.M. Tfaily, K. Heckman, and J.A. Davis (2017), “Characterization of natural organic matter in low-carbon sediments: Extraction and analytical approaches.” Organic Geochemistry, 114, 12-22, DOI:10.1016/j.orggeochem.2017.08.009
Team photo from the 2017 Retreat at the Hotel Shattuck Plaza in Berkeley, CA
Over 80 team members and collaborators attended the 2017 SFA Annual Retreat in Berkeley, CA. Read more »
This video of our “Meet the Scientist” series highlights the DOE-funded research activities of Rick Colwell (Oregon State) and Laura Lapham (Univ. Maryland). Rick and Laura were at East River this past weekend (photo below), where they installed multiple “osmosamplers” within the watershed including within a 200-ft deep Mancos shale well and within the East River at our Pumphouse location. These samplers rely upon creation of an osmotic potential that induces continuous flow and enables autonomous sampling within locations made inaccessible due to location (deep boreholes) and weather (snow / ice). Learn more about their work and the technology in the video.
Virrtual site tour highlighting one of the groundwater discharge zones into the East River being studied by Marty Briggs (USGS) and his collaborators Fred Day Lewis (USGS) and Lee Slater (Rutgers). With this time of the year dominated by baseflow contributions, the impact of geochemically reduced groundwater hitting oxic surface water is visually pronounced.
Drilling at our “Upper Elevation” site was completed in advance of a winter storm that hit Crested Butte yesterday allowing the rig to descend safely from the 11,200-ft elevation drill site. Both the coring and vertically resolved hydrologic testing in the well bore were hugely successful thanks to Authentic Drilling and the hard onsite work and advance planning of USGS scientists Andy Manning and Lyndsay Ball (photo attached). Core recovery was excellent, approaching nearly 100% over the entire depth (ca. 270-ft).
As concerns the DOE-funded work by USGS scientists in the Redwell Basin, a link to an interview with Andy and Lyndsay follows.
Lastly, life in the west — and in our watershed specifically — brings us into contact with ranchers and their cattle. Ranchers are critical members of the Crested Butte / Gunnison community and a group of important stakeholders in the watershed that we engage to develop cattle-friendly research activities and infrastructure. RMBL serves as a key ally and primary facilitator for engaging the local ranching community, so a reminder to reach out to the RMBL Science Director, Jennie Reithel, and Ken Williams before working in areas where cattle will be present during the summer and fall seasons.
Pumphouse cattle drive:
Meet the Scientist: Andy Manning and Lyndsay Ball:
Redwell Basin drilling:
Upper Elevation site core recovery:
Upper Elevation site hydrologic testing:
Hydrogen peroxide concentrations across the Rifle, CO field site.
Yuan et al. (2017) reports on the first measurement of the presence of hydrogen peroxide concentrations in groundwaters. Hydrogen peroxide and an associated class of compounds called reactive oxygen species have long been known to be important drivers of biogeochemical cycling and contaminant decomposition in surface water (oceans, rivers, and lakes). However, their importance in groundwater was unestablished.
By demonstrating that hydrogen peroxide and therefore the associated group of reactive oxygen species were widely distributed in the groundwaters of our site, the study establishes that they are likely important to the chemistry and function of groundwater systems. The widespread presence of reactive oxygen species may be an explanation for apparent non-equilibrium conditions in some waters as well as organic matter oxidation pathways without other obvious causes. Finally by showing that concentrations tended to be highest at transition zones the work focuses the likely most impactful areas of future investigation.
The commonly held assumption that photodependent processes dominate H2O2 production in natural waters has been recently questioned. This paper demonstrated for the unrecognized and light-independent generation of H2O2 in groundwater of an alluvial aquifer adjacent to the Colorado River near Rifle, CO. In situ detection using a sensitive chemiluminescent method suggests H2O2 concentrations ranging from lower than the detection limit (<1 nM) to 54 nM along the vertical profiles obtained at various locations across the aquifer. Our results also suggest dark formation of H2O2 is more likely to occur in transitional redox environments where reduced elements (e.g., reduced metals and NOM) meet oxygen, such as oxic–anoxic interfaces. A simplified kinetic model involving interactions among iron, reduced NOM, and oxygen was able to reproduce roughly many, but not all, of the features in our detected H2O2 profiles, and therefore there are other minor biological and/or chemical controls on H2O2 steady-state concentrations in such aquifer. Because of its transient nature, the widespread presence of H2O2 in groundwater suggests the existence of a balance between H2O2 sources and sinks, which potentially involves a cascade of various biogeochemically important processes that could have significant impacts on metal/nutrient cycling in groundwater-dependent ecosystems, such as wetlands and springs. More importantly, our results demonstrate that reactive oxygen species are not only widespread in oceanic and atmospheric systems but also in the subsurface domain, possibly the least understood component of biogeochemical cycles.
Yuan, X., P. S. Nico, X. Huang, T. Liu, C. Ulrich, K. H. Williams, and J. A. Davis (2017), Production of hydrogen peroxide in groundwater at Rifle, Colorado, Environ. Sci. Technol., DOI: 10.1021/acs.est.6b04803.
East River floodplain:
N.B. I failed to note in my narration of the floodplain visit the relationship of the presented work with the recently installed water quality monitoring station deployed by Joel Rowland (LANL); Joel’s multi-parameter probe, as described on the last Watershed Function Science Community Call, is located immediately downstream of this video location.
Redwell Basin drilling:
Bonus photo: Headwaters of Oh-Be-Joyful Creek, taken in late September 2017. The creek has a confluence with Redwell Creek emanating from the eponymous basin some miles downstream of this photo.
Credit: David Holub/Special to the Herald
Heidi Steltzer contributed an Op-Ed to the Durango Herald entitled “Protecting people through the science of studying plants”. In her piece, Steltzer highlights some of the insights gained by studying plants, including in mountainous watersheds. Read the full story here.
Comparing U(VI) breakthrough curves at a monitoring well location (FSB110D) in the F-Area of the Savannah River Site (SRS) using two model simulations: the electrostatic surface complexation model (SCM) and the best-fit NEM.
Arora et al. (2017) developed a simple non-electrostatic model through a step-by-step calibration procedure to describe U plume behavior at the Savannah River site. This simple model was found to be more numerically-efficient than a complex mechanistic model with electrostatic correction terms in predicting long-term U behavior at the site and by extension other uranium contaminated sites.
Uranium geochemistry has been extremely challenging to describe and predict. Although complex mechanistic models have been used to describe U sorption in field settings, there is significant uncertainty in model predictions due to scarce field data and modeling assumptions concerning mineral assemblage and subsurface heterogeneity. This study demonstrates that a simpler non-electrostatic model is a powerful alternative for describing U plume evolution at the Savannah River Site (SRS) because it can describe U(VI) sorption much more accurately than a constant coefficient (Kd) approach, while being more numerically efficient than a complex model with electrostatic correction terms. This study provides valuable insight into predicting uranium plume persistence from contaminated sites using simple non-electrostatic models.
The aim of this study was to test if a simpler, semi-empirical, non-electrostatic U(VI) sorption model (NEM) could achieve the same predictive performance as a model with electrostatic correction terms in describing pH and U(VI) behavior at multiple locations within the SRS F-Area. Modeling results indicate that the simpler NEM was able to perform as well as the electrostatic surface complexation model especially in simulating uranium breakthrough tails and long-term trends. However, the model simulations differed significantly during the early basin discharge period. Model performance cannot be assessed during this early period due to a lack of field observations (e.g., initial pH of the basin water) that would better constrain the models. In this manner, modeling results highlight the importance of the range of environmental data that are typically used for calibrating the model.
Arora, B., Davis, J. A., Spycher, N. F., Dong, W., & Wainwright, H. M. (2017). Comparison of Electrostatic and Non‐Electrostatic Models for U (VI) Sorption on Aquifer Sediments. Groundwater. doi: 10.1111/gwat.12551
A U.S. Department of Energy National Laboratory Managed by the University of California