The Hydrogeology of Los Alamos National Laboratory: Site History and Overview of Vadose Zone and Groundwater Issues

Newman, Brent D.; Robinson, Bruce A.

doi:10.2136/vzj2005.0072

Cited by 8 publications

(3 citation statements)

References 20 publications

(20 reference statements)

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“…Mean annual precipitation is 400 mm and exhibits a bimodal distribution between winter snowfall and summer monsoon showers. This has been the site of extensive research on ecology and hydrology (Lajtha and Barnes, 1991;Breshears et al, 1997;Newman and Robinson, 2005;Rich et al, 2008) and on the isotopic fluxes associated with photosynthesis and respiration at leaf, soil, and ecosystem scales (McDowell et al, 2008b;Bickford et al, 2009Bickford et al, , 2010Powers et al, 2010, Shim et al, 2011.…”

Section: Field Sitementioning

confidence: 99%

Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

Shim¹,

Powers²,

Meyer³

et al. 2013

Preprint

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We conducted high frequency measurements of the δ18O value of atmospheric CO2 from a juniper (Juniperus monosperma) woodland in New Mexico, USA, over a four-year period to investigate climatic and physiological regulation of the δ18O value of ecosystem respiration (δR). Rain pulses reset δR with the dominant water source isotope composition, followed by progressive enrichment of δR. Transpiration (ET) was significantly related to post-pulse δR enrichment because leaf water δ18O value showed strong enrichment with increasing vapor pressure deficit that occurs following rain. Post-pulse δR enrichment was correlated with both ET and the ratio of ET to soil evaporation (ET / ES). In contrast, soil water δ18O value was relatively stable and δR enrichment was not correlated with ES. Model simulations captured the large post-pulse δR enrichments only when the offset between xylem and leaf water δ18O value was modeled explicitly and when a gross flux model for CO2 retro-diffusion was included. Drought impacts δR through the balance between evaporative demand, which enriches δR, and low soil moisture availability, which attenuates δR enrichment through reduced ET. The net result, observed throughout all four years of our study, was a negative correlation of post-precipitation δR enrichment with increasing drought

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Section: Field Sitementioning

confidence: 99%

Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

Shim¹,

Powers²,

Meyer³

et al. 2013

Preprint

View full text Add to dashboard Cite

show abstract

“…Mean annual precipitation is 400 mm and exhibits a bimodal distribution between winter snowfall and summer monsoon showers. This has been the site of extensive research on ecology and hydrology (Lajtha & Barnes, 1991; Breshears et al , 1997; Newman & Robinson, 2005; Rich et al , 2008) and on the isotopic fluxes associated with photosynthesis and respiration at leaf, soil, and ecosystem scales (McDowell et al , 2008a; Bickford et al , 2009, 2010; Powers et al , 2010).…”

Section: Methodsmentioning

confidence: 99%

The role of interannual, seasonal, and synoptic climate on the carbon isotope ratio of ecosystem respiration at a semiarid woodland

Shim

Powers

Meyer

et al. 2011

Global Change Biology

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The terrestrial carbon cycle is influenced by environmental variability at scales ranging from diurnal to interannual. Here, we present 5-years of growing season (day 131-275) observations of the carbon isotope ratio of ecosystem respiration (d 13 C R ) from a semiarid woodland. This ecosystem has a large necromass component resulting from 97% Pinus edulis mortality in 2002, is dominated by drought-tolerant Juniperus monosperma trees, and experiences large variability in the timing and intensity of seasonal and synoptic water availability. Mean growing season d 13 C R was remarkably invariant (À23.57 AE 0.4%), with the exception of particularly enriched d 13 C R in 2006 following a winter with anomalously low snowfall. d 13 C R was strongly coupled to climate during premonsoon periods ($May to June), including fast ( 2 days) responses to changes in crown-level stomatal conductance (G c ) and vapor pressure deficit (vpd) following rain pulses. In contrast, d 13 C R was relatively decoupled from G c and environmental drivers during monsoon and postmonsoon periods (July-August and September, respectively), exhibiting only infrequent couplings of d 13 C R to vpd and soil water content (SWC) with longer lags ($ 8 days) and variable response slopes (both positive and negative). Notably, d 13 C R exhibited consistent dynamics after rainfall events, with depleted d 13 C R occurring within 1 h, progressive hourly d 13 C R enrichment over the remainder of the night, and net d 13 C R depletions over the multiple nights postevent in monsoon and postmonsoon periods. Overall this ecosystem demonstrated strong dependence of d 13 C R on precipitation, with an apparent dominance by the autotrophic d 13 C signal in premonsoon periods when deep soil moisture is abundant and surface soil moisture is low, and weaker coupling during monsoonal periods consistent with increasing heterotrophic dominance when deep soil moisture has declined and surface moisture is variable.

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“…The surface impoundments are located on the Pajarito Plateau on the eastern flank of the Jemez Mountains in northern New Mexico (Figure 1. [19]). The plateau is composed of finger mesas with deep canyons carved into the rocks of the Bandelier Tuff over the last 1.6 M years [20].…”

Section: Site Descriptionmentioning

confidence: 99%

Vadose Zone Transport of Tritium and Nitrate under Ponded Water Conditions

Stauffer¹,

Newman²,

Birdsell³

et al. 2022

Geosciences

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Vadose zone transport of tritium and nitrate can be important considerations at radioactive waste sites, landfills, or areas with industrial impacts. These contaminants are of particular concern because they typically have a relatively higher mobility in the subsurface compared to other compounds. Here, we describe a semiarid site with tritium and nitrate contamination involving a manmade ponded water source above a thick unsaturated zone at Los Alamos National Laboratory in New Mexico, USA. This study demonstrates the value of vadose zone flow and transport modeling for the development of field investigation plans (i.e., identifying optimal borehole locations and depths for contaminant characterization), and how a combination of modeling with isotope and geochemical measurements can provide insight into how tritium and nitrate transport in the vadose zone in semiarid environments. Modeling results suggest that at this location, tritium transport is well predicted by classical multiphase theory. Our work expands the demonstrated usefulness of a standard tritium conceptual model to sites with ponded surface conditions and agrees with previous results where a standard model was able to explain the evolution of a tritium plume at an arid waste disposal site. In addition, depth-based analyses of δ18O and δ2H of pore waters helped confirm the extent of pond infiltration into the vadose zone, and the δ15N of nitrate showed that the contaminant release history of the site was different than originally assumed.

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The Hydrogeology of Los Alamos National Laboratory: Site History and Overview of Vadose Zone and Groundwater Issues

Cited by 8 publications

References 20 publications

Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

Hydrologic control of the oxygen isotope ratio of ecosystem respiration in a semi-arid woodland

The role of interannual, seasonal, and synoptic climate on the carbon isotope ratio of ecosystem respiration at a semiarid woodland

Vadose Zone Transport of Tritium and Nitrate under Ponded Water Conditions

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