Now showing items 10929-10948 of 14830

    • Quantified Assessment of the Meteorological Variables Facilitating the Establishment of the Karakoram Anomaly

      Gupta, Hoshin V.; Bashir, Furrukh; Gupta, Hoshin V.; Zeng, Xubin; Hazenberg, Pieter (The University of Arizona., 2016)
      Lofty Hindukush, Karakoram and Himalayan (HKH) mountain ranges centered in the Northern Pakistan are host to some of the world’s largest glaciers outside the Polar Regions and are a source of water for drinking and irrigation to the millions of people living downstream. With the increase in the global temperatures, glaciers are reported as retreating globally. However, some of the glaciers in the Karakoram mountain ranges are reported as surging with positive mass balance, especially since the 1990s. This phenomenon is described as "The Karakoram Anomaly". Various efforts have been made to explain the state and fate of the HKH glaciers in the recent past. However, they are limited to quantification of the change in temperature, precipitation and river runoff, or through their impact on future climate projections. For the HKH region, temperature fluctuations have been out of the phase with hemispheric trends for past several centuries. Therefore, climate change in this region is not solely the temperature effect on melting as compared to other glaciated regions. To identify the reasons for the establishment of the Karakoram Anomaly, monthly mean climatic variables for last five decades, reported from meteorological observatories at the valley floors in HKH region, are analyzed. In addition to the climatic variables of temperature and precipitation, monthly mean synoptic observations reported by meteorological observatories in both morning and afternoon, along with monthly mean radiosonde data are used. From these data the role of different near-surface and upper atmospheric meteorological variables in maintaining the positive mass balance of the glaciers and the development of the Karakoram Anomaly can be explained. An overall warming in the region is observed. The trends in the summer temperatures, which were reported as decreasing a decade ago, are now found as increasing in updated time series. However, the overall gradient is still negative. The winter mean and maximum temperatures are increasing with accelerated trends. Both maximum and minimum temperatures in summer are not diverging anymore and the diurnal temperature range is decreasing in the most recent decade. The afternoon cloudiness is found as increasing throughout the year except for spring, which is indicative of an increase in convective uplifting. Moreover, humidity is increasing all over the region; due to evaporation in the spring, from monsoon moisture advection in summer, and due to the recycling of monsoon moisture in autumn. Furthermore, near-surface wind speed and net radiation in the region are decreasing, explaining the decrease in the summer minimum temperature and the presence of the cloudy skies. The decrease in near-surface wind speed, and net radiation, and increase in water vapor pressure put a limit on the evapotranspiration process. In addition, winter and summer precipitation is increasing. The aridity index, which is based on the ratio of precipitation and reference evaporation, indicates that region is turning moisture surplus and energy deficient. Surface atmospheric pressure and 700 hPa geopotential height is increasing due to warming in the bottom layers of the troposphere. Nighttime inversion in the lower tropospheric layers is decreasing due to warming. Analysis of gridded observed and reanalysis datasets indicates that they are not presenting a signal of change in accordance with the instrumental record. Furthermore, it is found that meteorological conditions during the summer season are still favorable for the sustenance of glaciers whereas more melting may occur in the spring season that may increase the early season river flows and may affect lower lying portions of the debris-free glaciers.
    • Quantifying baseflow inputs to the San Pedro River : a geochemical approach

      Baillie, Matthew Nelson.; Ekwurzel, Brenda; Hogan, James (The University of Arizona., 2005)
      The Upper San Pedro River Basin (Arizona, U.S.A.) contains one of the few remaining desert riparian areas in the Southwest. This study characterizes and quantifies the water sources that contribute to riparian groundwater and sustain river baseflow using a suite of geochemical tracers including stable and radioactive isotopes and anions. Results indicate that of the possible sources, basin groundwater from the west and local recharge of monsoon floodwaters are the most significant water sources to the riparian system. Using a simple two end-member mixing model, riparian groundwater varies from 10 to 90% basin groundwater whereas baseflow ranges from 0 to 55%; the percentage is well correlated with gaining (basin groundwater dominated) and losing reaches (monsoon dominated). These results highlight the importance of monsoon floodwater recharge as a water source for desert riparian systems, a fact that future water management decisions need to address.
    • Quantifying Biomass from Point Clouds by Connecting Representations of Ecosystem Structure

      Barron-Gafford, Greg A.; Hendryx, Sean Michael; Swetnam, Tyson; van Leeuwen, Wim (The University of Arizona., 2017)
      Quantifying terrestrial ecosystem biomass is an essential part of monitoring carbon stocks and fluxes within the global carbon cycle and optimizing natural resource management. Point cloud data such as from lidar and structure from motion can be effective for quantifying biomass over large areas, but significant challenges remain in developing effective models that allow for such predictions. Inference models that estimate biomass from point clouds are established in many environments, yet, are often scale-dependent, needing to be fitted and applied at the same spatial scale and grid size at which they were developed. Furthermore, training such models typically requires large in situ datasets that are often prohibitively costly or time-consuming to obtain. Here, we present a novel scale- and sensor-invariant framework for efficiently estimating biomass from point clouds. Central to this framework, we present a new algorithm, which we term Assign Points To Existing Clusters (APTEC), developed for finding matches between in situ data and clusters in remotely-sensed point clouds. This algorithm can be used for assessing canopy segmentation accuracy and for training and validating machine learning models for predicting biophysical variables. We demonstrate the algorithm's efficacy by using it to train a random forest model of aboveground biomass in a shrubland environment in Southern Arizona. We show that by learning a nonlinear function to estimate biomass from segmented canopy features, we can reduce error, especially in the presence of inaccurate clusterings, when compared to a traditional, deterministic technique to estimate biomass from remotely measured canopies. Importantly, our random forest on cluster features model extends established methods of training random forest regressions to predict biomass of subplots but requires significantly less training data and is scale invariant. This model reduced mean absolute error, when evaluated on all test data in leave-one-out cross-validation by 41% from deterministic mesquite allometry and 36.2% from the inferred ecosystem-state allometric function on terrestrial lidar data. Our best performing model reduced mean absolute error across all data sources by 22.5%. Our framework should allow for the inference of biomass more efficiently than common subplot methods and more accurately than individual tree segmentation methods in vegetated environments in which accurate segmentation of individual plants is difficult.

      Brooks, Paul; Koch, Joshua Charles (The University of Arizona., 2005)
      This study is designed to quantify the presence and transport potential of carbon (C) and nitrogen (N) from the dominant landscapes and vegetation types to the stream/riparian ecosystem along the San Pedro River in southeastern AZ. Previous biogeochemical studies of desert streams have focused largely on nutrient cycling within the riparian corridor, with significantly less research on linkages between uplands and the stream system. Surface water inputs during monsoon storms account for 65% of the water balance, and may also be an important component of nutrient inputs to semi-arid streams. Quantifying the bulk C and N of shrub lands and grasslands in the upland, terrace, and riparian forest soils and litters, and conducting experiments to measure potentially-mobile fractions of these pools allows for estimation of potential loads from subwatersheds to the San Pedro River of southern Arizona. Organic matter amounts and anion chemistry from first and second order ephemeral flows were statistically similar to amounts measured in laboratory leach tests of upland soils. Upland and terrace slopes displayed similar bulk C and N, while terraces displayed higher extractable C and N. Higher potential inputs from terraces may be offset by the decreased flood potential in the near-stream environment. Higher C and Nin shrubland runoff, coupled with woody encroachment in the uplands may increase C and N inputs in subsequent years.
    • Quantifying catchment scale soil variability in Marshall Gulch, Santa Catalina Mountains Critical Zone Observatory

      Rasmussen, Craig; Holleran, Molly E.; Chorover, Jon; Guertin, David P. (The University of Arizona., 2013)
      The quantification and prediction of soil properties is fundamental to further understanding the Critical Zone (CZ). In this study we aim to quantify and predict soil properties within a forested catchment, Marshall Gulch, AZ. Input layers of soil depth (modeled), slope, Saga wetness index, remotely sensed normalized difference vegetation index (NDVI) and national agriculture imagery program (NAIP) bands 3/2 were determined to account for 95% of landscape variance and used as model predictors. Target variables including soil depth (cm), carbon (kg/m²), clay (%), Na flux (kg/m²), pH, and strain are predicted using multivariate linear step-wise regression models. Our results show strong correlations of soil properties with the drainage systems in the MG catchment. We observe deeper soils, higher clay content, higher carbon content, and more Na loss within the drainages of the catchment in contrast to the adjacent slopes and ridgelines.
    • Quantifying Catchment-Scale Particulate Organic Matter (POM) Loss Following Fire, Relative to Background POM Fluxes

      Brooks, Paul D.; Condon, Katherine Elyse; Pelletier, Jon D.; Meixner, Thomas (The University of Arizona., 2013)
      This study investigates translocation of particulate carbon and nitrogen from burned and unburned catchments within New Mexico's Valles Caldera National Preserve following severe wildfire. My research questions are: (1) how much carbon and nitrogen is eroded from burned slopes and re-deposited in debris fans? and (2) how do these quantities compare to fluvial export of particulate carbon and nitrogen from nearby unburned catchments? Results indicate that the ~200 kg ha⁻¹ of nitrogen per depositional area on the debris fans represents ~50 to 100 years' worth of atmospheric inputs. In total, 124 times more carbon and 21 times more nitrogen were deposited on the two fans than was exported in particulate form from all three unburned catchments combined in water year 2012. My findings suggest that post-fire erosion may increase nitrogen loading to downslope environments, with the potential to alter the biogeochemical budgets of both aquatic and terrestrial systems.
    • Quantifying Crustal Thickness Over Time in Magmatic Arcs

      Ducea, Mihai N.; Profeta, Lucia Rodica; Ducea, Mihai N.; Quade, Jay; Zandt, George (The University of Arizona., 2017)
      We present global and regional correlations between whole-rock values of Sr/Y and La/Yb and crustal thickness for intermediate rocks from modern subduction-related magmatic arcs formed around the Pacific. These correlations bolster earlier ideas that various geochemical parameters can be used to track changes of crustal thickness through time in ancient subduction systems. Inferred crustal thicknesses using our proposed empirical fits are consistent with independent geologic constraints for the Cenozoic evolution of the central Andes, as well as various Mesozoic magmatic arc segments currently exposed in the Coast Mountains, British Columbia, and the Sierra Nevada and Mojave- Transverse Range regions of California. We propose that these geochemical parameters can be used, when averaged over the typical lifetimes and spatial footprints of composite volcanoes and their intrusive equivalents to infer crustal thickness changes over time in ancient orogens.
    • Quantifying Mesoscale Soil Moisture with the Cosmic-Ray Rover

      Zreda, Marek; Chrisman, Bobby Brady; Zeng, Xubin; Shuttleworth, Jim; Franz, Trenton (The University of Arizona., 2013)
      Existing techniques measure soil moisture either at a point or over a large area many kilometers across. To bridge these two scales, we used the mobile cosmic-ray probe, or cosmic-ray rover, an instrument similar to the recently developed COSMOS probe, but bigger and mobile. This study explores the challenges and opportunities for making maps of soil moisture over large areas using the cosmic-ray rover. In 2012, soil moisture was mapped 22 times in a 25 km x 40 km survey area of the Tucson Basin at 1 km² resolution, i.e., at a scale comparable to that of a pixel for the Soil Moisture and Ocean Salinity (SMOS) satellite mission. The soil moisture distribution is influenced mainly by climatic variations, notably by the North American monsoon, which resulted in a systematic change in the regional variance as a function of the mean soil moisture.
    • Quantifying mountain system recharge in the upper San Pedro basin, Arizona, Using geochemical tracers

      Ekwurzel, Brenda; Wahi, Arun Kumar; Ekwurzel, Brenda (The University of Arizona., 2005)
      Use of geochemical tracers has improved our conceptual and quantitative understanding of mountain system recharge (MSR) in the Upper San Pedro Basin, Arizona. These isotopic, major anion, and noble gas tracers resolved the location, rate and seasonality of recharge as well as groundwater flowpaths and residence times. Detectable anthropogenic 14C and tritium revealed less than 50 years residence times for the fast fraction of flow on the mountain block and in riparian areas. Maximum 14C residence times of over 10,000 years occurred for basin groundwater entering the San Pedro River riparian area. Groundwater fluxes determined from 14C imply MSR rates between 2 x 10^6 m^3 /yr and 9 x 10^6 m^3 /yr. Stable isotopic signatures indicate that MSR has a 40-90% contribution from winter precipitation and a 10-60% contribution from summer precipitation. Geochemical data is recommended to help calibrate groundwater flow models and substantially reduce uncertainty in the estimated MSR rate.
    • Quantifying Power and Bias in Cluster Randomized Trials Using Mixed Models vs. Cluster-Level Analysis in the Presence of Missing Data: A Simulation Study

      Bell, Melanie; Vincent, Brenda; Roe, Denise; Hsu, Chiu-Hsieh (The University of Arizona., 2016)
      In cluster randomized trials (CRTs), groups are randomized to treatment arms rather than individuals while the outcome is assessed on the individuals within each cluster. Individuals within clusters tend to be more similar than in a randomly selected sample, which poses issues with dependence, which may lead to underestimated standard errors if ignored. To adjust for the correlation between individuals within clusters, two main approaches are used to analyze CRTs: cluster-level and individual-level analysis. In a cluster-level analysis summary measures are obtained for each cluster and then the two sets of cluster-specific measures are compared, such as with a t-test of the cluster means. A mixed model which takes into account cluster membership is an example of an individual-level analysis. We used a simulation study to quantify and compare power and bias of these two methods. We further take into account the effect of missing data. Complete datasets were generated and then data were deleted to simulate missing completely at random (MCAR) and missing at random (MAR) data. A balanced design, with two treatment groups and two time points was assumed. Cluster size, variance components (including within-subject, within-cluster and between-cluster variance) and proportion of missingness were varied to simulate common scenarios seen in practice. For each combination of parameters, 1,000 datasets were generated and analyzed. Results of our simulation study indicate that cluster-level analysis resulted in substantial loss of power when data were MAR. Individual-level analysis had higher power and remained unbiased, even with a small number of clusters.
    • Quantifying rangeland health indicators using runoff and sediment from rainfall simulator experiments.

      Blumenfeld, Hana Devorah.; Guertin, D. Phillip; Stone, Jeffrey; Paige, Ginger (The University of Arizona., 2002)
      The objective of this study is to analyze the relationship between rangeland health indicators and runoff and erosion for different ecological sites. An investigation of intersite and intrasite variability of the indicators was also conducted. Research was performed across five ecological sites in typic condition within MLRA 41-3 on 3-6 plots per site. Point intercept (400 points per plot) and gap intercept (3 slope and 5 contour) measurements recorded on each of the 2 m by 6.1 m plots. Runoff and sediment yield data obtained from rainfall simulator experiments on corresponding plots were related to the indicator data. This study illustrates the possibility of using hydrologic data to quantify rangeland health indicators. The introduction of two burned ecological sites provided the opportunity to assess the indicators' ability to relate to runoff and erosion for different site conditions. This research result indicated that runoff and sediment yield have a positive relationship with gap length and a negative relationship with amount of cover.
    • Quantifying seasonal variations in water source and nutrient concentrations: a catchment comparison in Valles Caldera National Preserve, NM, USA

      Brooks, Paul D.; Kostrzewski, Jennifer Marie; Brooks, Paul D. (The University of Arizona., 2006)
      The purpose of this study is to examine the interactions between physical and biological processes, and their influence on nutrient cycling and export in two semiarid, montane, headwater catchments. We measured stream chemistry in two neighboring catchments within the Valles Caldera National Preserve, New Mexico from February through August 2005 to identify (1) how variable water sources and flowpaths affect carbon and nutrient concentrations, and (2) how these solutes were modified as they were transported out of the catchments. Both catchments were characterized by a large snowmelt flush of carbon and nutrients in spring and a smaller flush of carbon and nutrients during the monsoon season. Although similar in elevation, soil, vegetation, and climate, the catchments exhibited significantly differences in stream water C, N, and P concentrations during the spring flush. End member mixing using conservative solutes identified the cause of this variability was due primarily to differences in hydro logic residence time and streamflow generation between catchments. These mixing models for each catchment indicated that variability in carbon and nutrients was explained by physical transport during the spring snowmelt and the first flushing events of the monsoon season. In contrast, conservative mixing did a poor job of predicting carbon and nutrient chemistry during other season suggesting biological modification during transport was a major control on streamwater chemistry. After correcting for variability in water sources, both catchments exhibited higher than expected N concentrations during winter and snowmelt, switching to higher than expected P concentrations during the summer monsoon season suggesting a seasonal switch in limiting nutrients. These data demonstrate how simple, quantitative evaluation of hydrologic flowpaths and residence time can be used to separate physical and biological controls on catchment-scale stream water chemistry.
    • Quantifying Spatial Variability of Snow Water Equivalent, Snow Chemistry, and Snow Water Isotopes: Application to Snowpack Water Balance

      Gustafson, Joseph Rhodes; Brooks, Paul D. (The University of Arizona., 2008)
      This study quantifies spatial and temporal patterns in snow water equivalent (SWE), chemistry, and water isotopes associated with snowpack shading due to aspect and vegetation in the Valles Caldera National Preserve, New Mexico. Depth, density, stratigraphy, temperature, and snow chemistry, isotope, and biogeochemical nutrient samples were collected and analyzed from five snowpit locations on approximate monthly intervals between January-April 2007. SWE showed little variability between sites in January (~10mm) but differences expanded to 84mm (30%) by max accumulation in open sites and 153mm (45%) between all sites. Sulfate varied by 22% (10.6-13.5 microeq/L), Cl- by 35% (17.4-26.9 microeq/L), and d18O by 17% (-16.3 to -13.5), with SWE exhibiting inverse correlations with d18O (r2=0.96), SO42- (r2=0.75), and Cl- (r2=0.60) at max accumulation. Regression relationships suggest variability in SWE and solutes/water isotopes are primarily driven by sublimation. Mass balance techniques estimate sublimation ranges from 1-16% between topographically- and non-shaded open sites.
    • Quantifying streamflow change following bark beetle outbreak in multiple central Colorado catchments

      Troch, Peter A.; Somor, Andrew; Troch, Peter A.; Brooks, Paul D.; Breshears, David D. (The University of Arizona., 2010)
      Over the last decade, millions of acres of western North American forest have been reduced to areas of standing dead trees following eruptions in bark beetle populations. This thesis provides up-to-date information on streamflow response to the recent bark beetle outbreak in subalpine forests of the Colorado Rockies. Streamflow and climate measures are evaluated in eight central Colorado catchments with long-term data records and varying levels of beetle outbreak. No detectable streamflow change is observed in 7 of 8 highly impacted catchments. A significant reduction in streamflow is observed in 1 highly impacted catchment and is likely driven by tree mortality and record warm temperatures. These findings deviate from expected results and have important implications for vegetation and streamflow change under a warmer climate.
    • Quantifying the Effects of Forest Canopy Cover on Net Snow Accumulation at a Continental, Mid-Latitude Site, Valles Caldera National Preserve, NM, USA

      Brooks, Paul D.; Veatch, William Curtis; Brooks, Paul D. (The University of Arizona., 2008)
      Although forest properties are known to influence snowpack accumulation and spring runoff, the processes underlying the impacts of forest canopy cover on the input of snowmelt to the catchment remain poorly characterized. In this study I show that throughfall and canopy shading can combine to result in maximal snowpacks in forests of moderate canopy density. Snow depth and density data taken shortly before spring melt in the Jemez Mountains of New Mexico show strong correlation between forest canopy density and snow water equivalent, with maximal snow accumulation in forests with density between 25 and 45%. Forest edges are also shown to be highly influential on local snow depth variability, with shaded open areas holding significantly deeper snow than either unshaded open or deep forest areas. These results are broadly applicable in improving estimates of water resource availability, predicting the ecohydrological implications of vegetation change, and informing integrated water resources management.
    • Quantifying the effects of forest vegetation on snow accumulation, ablation, and potential meltwater inputs, Valles Caldera National Preserve, NM, USA

      Brooks, Paul D.; Musselman, Keith N.; Brooks, Paul D. (The University of Arizona., 2006)
      I quantified the competing effects of forest vegetation on snow accumulation and ablation in a lower mid-latitude montane environment where solar radiation dominates winter snow-atmosphere energy fluxes and limited work has been focused. Detailed snowpit analyses and ultrasonic snow depth sensors indicated forest vegetation affected snowcover in three ways; canopy interception and sloughing, enhanced snowpack metamorphism and ablation, and shading of direct solar radiation. Competing accumulation and melt processes determine the snow cover duration, SWE yield, and potential meltwater inputs. On average, canopy interception resulted in 44% less SWE accumulating beneath the canopy. I observed an inverse correlation between snowpack density and grain size with distance from the tree bole at maximum accumulation. Larger grains and lower densities near the bole indicated enhanced metamorphism of the near tree snowpack. Snow surveys around 15 trees at max accumulation indicated that the north sides of trees had 24.6% (p=0.01) more SWE than south tree sides. Micro- to tree scale observations support our stand and catchment-scale finding that a shaded snowpack experiences increased SWE accumulation, decreased ablation and melt rates, and prolonged seasonal snow cover. Specifically, we found that vegetative shading may delay the basin average maximum SWE accumulation by up to three weeks and greatly increase snow cover duration by minimizing snowmelt rates. Data point to compelling differences in forest ablation and melt processes in this lower mid-latitude where enhanced insolation augments the physical processes observed elsewhere. A binary regression tree model indicated strong correlation (R 2 = 0.54) between micro-scale (i.e. 10-cm resolution) canopy structure indices and snow depth, suggesting that future remotely sensed vegetation data may improve snow distribution models. A better understanding of the effects of forest cover on a basin's snowpack will prepare us to more accurately predict the potentially wide-ranging hydrologic impacts of climate, land cover, and land use change in these seasonally snow covered forested environments.
    • Quantifying the erosion and transport process

      Knapp, Kerry Lance (The University of Arizona., 1979)
    • Quantifying the Role of Hydrologic Variability in Soil Carbon Flux

      Brooks, Paul D.; Stielstra, Clare M.; McIntosh, Jennifer C.; Chorover, Jon (The University of Arizona., 2012)
      Soil carbon (C) is the largest terrestrial carbon pool. While inputs to this system are fairly well constrained, the diverse factors driving soil C efflux remain poorly understood. Carbon in surface soils is mobilized via two distinct pathways: CO₂ gas flux and dissolved C flux. The goal of this study was to quantify the role of hydrologic variability in mobilizing carbon as gaseous and dissolved fluxes from near-surface soils, and to determine their relative magnitudes. Data were collected through 2010 and 2011 from two subalpine sites in Arizona and New Mexico. I observed no significant variability in dissolved fluxes, and these values were low at all sites. In contrast, CO₂ fluxes were large (from 0.22 g C m⁻² d⁻¹ to 5.27 g C m⁻² d⁻¹) and varied between sites and between years. My results suggest that in arid montane forests soil carbon flux is critically linked to water availability.
    • Quantitation of mismatched regions in DNA heteroduplexes: lambda phage DNA as a model system

      McCarthy, James Joseph, 1947- (The University of Arizona., 1974)
    • Quantitative aerosol studies of guinea pig anaphylaxis

      Tom, Baldwin H. (The University of Arizona., 1967)