Criteria and techniques for field characterization and modelingrelated to selecting and evaluating performance of LILW disposalsites

Argentina is faced with the challenging problem ofdeveloping technology for near-surface disposal and isolation of low- andintermediate-level radioactive waste (LILW). The preferred option fordisposal of LILW (including both relatively short-lived and long-livedradionuclides) is to use disposal facilities that arenear-surface--either above or below ground level [IAEA, 1985; 2001a;2004]. How individual components of a waste disposal system perform(including waste forms, waste containers, engineered barriers and hostenvironment) will determine system safety and the safety of thesurrounding environment [IAEA, 1999]. The lack of appropriate engineeringfor the backfill, and for the selection of sealing and covering materialsfor trenches, vaults, and ditches, could result in the escape ofradionuclides from the disposed wastes [IAEA, 1994a; 2001b]. Therefore,assessment and design of backfill, barriers, and cover materials are veryimportant, both for preventing invasion of water into the disposalsystem, and for retarding radionuclides that could potentially migratefrom the system into the atmosphere or groundwater [IAEA, 1982; 1994b;2001a]

Modeling the Impact of Liana Infestation on The Demography and Carbon Cycle of Tropical Forests

There is mounting empirical evidence that lianas affect the carbon cycle of tropical forests. However, no single vegetation model takes into account this growth form, although such efforts could greatly improve the predictions of carbon dynamics in tropical forests. In this study, we incorporated a novel mechanistic representation of lianas in a dynamic global vegetation model (the Ecosystem Demography Model). We developed a liana‐specific plant functional type and mechanisms representing liana–tree interactions (such as light competition, liana‐specific allometries, and attachment to host trees) and parameterized them according to a comprehensive literature meta‐analysis. We tested the model for an old‐growth forest (Paracou, French Guiana) and a secondary forest (Gigante Peninsula, Panama). The resulting model simulations captured many features of the two forests characterized by different levels of liana infestation as revealed by a systematic comparison of the model outputs with empirical data, including local census data from forest inventories, eddy flux tower data, and terrestrial laser scanner‐derived forest vertical structure. The inclusion of lianas in the simulations reduced the secondary forest net productivity by up to 0.46 tC ha−1 year−1, which corresponds to a limited relative reduction of 2.6% in comparison with a reference simulation without lianas. However, this resulted in significantly reduced accumulated above‐ground biomass after 70 years of regrowth by up to 20 tC/ha (19% of the reference simulation). Ultimately, the simulated negative impact of lianas on the total biomass was almost completely cancelled out when the forest reached an old‐growth successional stage. Our findings suggest that lianas negatively influence the forest potential carbon sink strength, especially for young, disturbed, liana‐rich sites. In light of the critical role that lianas play in the profound changes currently experienced by tropical forests, this new model provides a robust numerical tool to forecast the impact of lianas on tropical forest carbon sinks

Microbial Community Dynamics of Lactate Enriched Hanford Groundwaters

The Department of Energy site at Hanford, WA, has been historically impacted by U and Cr from the nuclear weapons industry. In an attempt to stimulate microbial remediation of these metals, in-situ lactate enrichment experiments are ongoing. In order to bridge the gap from the laboratory to the field, we inoculated triplicate anaerobic, continuous-flow glass reactors with groundwater collected from well Hanford 100-H in order to obtain a stable, enriched community while selecting for metal-reducing bacteria. Each reactor was fed from a single carboy containing defined media with 30 mM lactate at a rate of 0.223 ml/min under continuous nitrogen flow at 9 ml/min. Cell counts, organic acids, gDNA (for qPCR and pyrosequencing) and gases were sampled during the experiment. Cell counts remained low (less than 1x107 cells/ml) during the first two weeks of the experiment, but by day 20, had reached a density greater than 1x108 cells/ml. Metabolite analysis showed a decrease in the lactate concentrations over time. Pyruvate concentrations ranged from 20-40 uM the first week of the experiment then was undetectable after day 10. Likewise, formate appeared in the reactors during the first week with concentrations of 1.48-1.65 mM at day 7 then the concentrations decreased to 0.69-0.95 on day 10 and were undetectable on day 15. Acetate was present in low amounts on day 3 (0.15-0.33 mM) and steadily increased to 3.35-5.22 mM over time. Similarly, carbon dioxide was present in low concentrations early on and increased to 0.28-0.35 mM as the experiment progressed. We also were able to detect low amounts of methane (10-20 uM) during the first week of the experiment, but by day 10 the methane was undetectable. From these results and pyrosequencing analysis, we conclude that a shift in the microbial community dynamics occurred over time to eventually form a stable and enriched microbial community. Comprehensive investigations such as these allow for the examination of not only which nutrient source will accelerate site remediation, but also provide insight to evaluate remediation strategies through which enriched community members are important for bioremediation

Experiments and evaluation of chaotic behavior of dripping water in fracture models

Laboratory experiments of water seepage in smooth and rough-walled, inclined fracture models were performed and the monitoring data analyzed for evidence of chaos. One fracture model consisted of smooth, parallel glass plates separated by 0.36 mm. The second model was made with textured glass plates. The fracture model was inclined 60{sup o} from the horizontal. Water was delivered to the fracture model through a capillary tube in contact with the top fracture edge at constant flow rates. Three types of capillary tubes were used: (1) a stainless steel blunt needle of 0.18 mm ID for flow rates of 0.25 to 4 mL/hr, (2) a nylon tube of 0.8 mm ID for flow rates of 0.25 to 10 mL/hr, and (3) a glass tube of 0.75 mm ID for flow rates of 0.5 to 20 mL/hr. Liquid pressure was monitored upstream of the capillary tube. Visual observations showed that water seeped through the fracture models in discrete channels that underwent cycles of snapping and reforming. Observations also showed that liquid segments, or drips, detached at different points along the water channel. The measured liquid pressure responded to the growth and detachment of drips. Separate experiments were carried out to measure pressure time-trends for dripping into open air to compare these data with those obtained in fracture models. Analysis of the pressure time-trends included determination of the time lag from the minimum of the average mutual information function, the local and global embedding dimensions, Lyapunov exponents and the Lyapunov dimension, the Hurst exponent and the entropy as a function of the embedding dimension for each data set. Most of the water pressure data contain oscillations exhibiting chaotic behavior, with local embedding dimensions ranging from 3 to 10, and global embedding dimensions one to two units higher. The higher dimensionality of some of the data sets indicates either the presence of high-dimensional chaos or a significant random component. It was determined that the flow rate, which affects seepage behavior and is reflected in the pressure measurements, is inversely correlated with the Hurst exponent. This supports the hypothesis that at higher flow rates, the random component of seepage behavior (as represented by liquid pressure) increases. However, there was no simple, consistent correlation between the trends for the other diagnostic parameters of chaos and flow rate. Three-dimensional plots of selected data sets in pseudo-phase space exhibit definite structures with some scattering of data points on the attractor. All the analyses confirm that the pressure time trends that describe flow behavior are mostly characterized by low-dimensional, deterministic chaotic dynamics with some random component

Simulating infiltration tests in fractured basalt at the Box Canyon Site, Idaho

The results of a series of ponded infiltration tests in variably saturated fractured basalt at Box Canyon, Idaho, were used to build confidence in conceptual and numerical modeling approaches used to simulate infiltration in fractured rock. Specifically, we constructed a dual-permeability model using TOUGH2 to represent both the matrix and fracture continua of the upper basalt flow at the Box Canyon site. A consistent set of hydrogeological parameters was obtained by calibrating the model to infiltration front arrival times in the fracture continuum as inferred from bromide samples collected from fracture/borehole intersections observed during the infiltrating tests. These parameters included the permeability of the fracture and matrix continua, the interfacial area between the fracture and matrix continua, and the porosity of the fracture continuum. To calibrate the model, we multiplied the fracture-matrix interfacial area by a factor between 0.1 and 0.01 to reduce imbibition of water from the fracture continuum into the matrix continuum during the infiltration tests. Furthermore, the porosity of the fracture continuum, as calculated using the fracture aperture inferred from pneumatic-test permeabilities, was increased by a factor of 50 yielding porosity values for the upper basalt flow in the range of 0.01 to 0.02. The fracture-continuum porosity was a highly sensitive parameter controlling the arrival times of the simulated infiltration fronts. Porosity values are consistent with those determined during the Large-Scale Aquifer Pumping and Infiltration Test at the Idaho National Engineering and Environmental Laboratory

Interpreting water demands of forests and grasslands within a new Budyko formulation of evapotranspiration using percolation theory

The relationship between carbon cycle and water demand is key to understanding global climate change, vegetation productivity, and predicting the future of water resources. The water balance, which enumerates the relative fractions of precipitation P that run off, Q, or are returned to the atmosphere through evapotranspiration, ET, links drawdown of atmospheric carbon with the water cycle through plant transpiration. Our theoretical description based on percolation theory proposes that dominant ecosystems tend to maximize drawdown of atmospheric carbon in the process of growth and reproduction, thus providing a link between carbon and water cycles. In this framework, the only parameter is the fractal dimensionality df of the root system. Values of df appear to relate to the relative roles of nutrient and water accessibility. Larger values of df lead to higher ET values. Known ranges of grassland root fractal dimensions predict reasonably the range of ET(P) in such ecosystems as a function of aridity index. Forests with shallower root systems, should be characterized by a smaller df and, therefore, ET that is a smaller fraction of P. The prediction of ET/P using the 3D percolation value of df matches rather closely results deemed typical for forests based on a phenomenology already in common use. We test predictions of Q with P against data and data summaries for sclerophyll forests in southeastern Australia and the southeastern USA. Applying PET data from a nearby site constrains the data from the USA to lie between our ET predictions for 2D and 3D root systems. For the Australian site, equating cited “losses” with PET underpredicts ET. This discrepancy is mostly removed by referring to mapped values of PET in that region. Missing in both cases is local PET variability, more important for reducing data scatter in southeastern Australia, due to the greater relief

Variation in hydroclimate sustains tropical forest biomass and promotes functional diversity.

The fate of tropical forests under climate change is unclear as a result, in part, of the uncertainty in projected changes in precipitation and in the ability of vegetation models to capture the effects of drought-induced mortality on aboveground biomass (AGB). We evaluated the ability of a terrestrial biosphere model with demography and hydrodynamics (Ecosystem Demography, ED2-hydro) to simulate AGB and mortality of four tropical tree plant functional types (PFTs) that operate along light- and water-use axes. Model predictions were compared with observations of canopy trees at Barro Colorado Island (BCI), Panama. We then assessed the implications of eight hypothetical precipitation scenarios, including increased annual precipitation, reduced inter-annual variation, El Niño-related droughts and drier wet or dry seasons, on AGB and functional diversity of the model forest. When forced with observed meteorology, ED2-hydro predictions capture multiple BCI benchmarks. ED2-hydro predicts that AGB will be sustained under lower rainfall via shifts in the functional composition of the forest, except under the drier dry-season scenario. These results support the hypothesis that inter-annual variation in mean and seasonal precipitation promotes the coexistence of functionally diverse PFTs because of the relative differences in mortality rates. If the hydroclimate becomes chronically drier or wetter, functional evenness related to drought tolerance may decline