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Open Access Publications from the University of California

Scholarly Works (13 results)

  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2016)
    Cover page: Beryllium desorption from minerals and organic ligands over time
    • Article
    • Peer Reviewed
    UC San Diego Previously Published Works (2016)
    Environmental contextBeryllium is a toxic environmental contaminant but has many industrial and scientific applications. Our work explores the effects of soil composition on beryllium retention, focussing on organic matter, mineralogy and pH and concludes that phosphorus and sulfur oxides in addition to soil acidity are strong controls on beryllium mobility. These results aid in future predictions regarding the fate of beryllium in the environment. AbstractUnderstanding the chemical controls on beryllium sorption is fundamental when assessing its mobility as a pollutant and interpreting its concentration as a geochemical tracer of erosion, weathering and landscape surface stability. In order to evaluate the interactions of beryllium with soil- and aquatic-related materials, we selected model organic compounds and minerals to perform sorption experiments. The retention of beryllium by each of these compounds and minerals was evaluated over a pH range of 3–6 and at various equilibration times to determine which conditions allowed the greatest retention of beryllium. We conclude that most beryllium sorption occurred within 24h for both organic and mineral materials. However, equilibration required longer periods of time and was dependent on the solution pH and sorbent material. The pH exhibited a strong control on beryllium sorption with distribution coefficient (Kd) values increasing non-linearly with increasing pH. A system with a pH of 6 is likely to retain 79–2270% more beryllium than the same system at a pH of 4. Phosphonate retained the greatest amount of beryllium, with Kd values 2–30× greater than all other materials tested at a pH of 6. Therefore, soils containing larger amounts of phosphorus-bearing minerals could result in greater retention of beryllium relative to phosphorus-limited soils. Overall, soil composition, with an emphasis on phosphorus oxide content and pH, is an important property to consider when evaluating the capacity of a system to retain beryllium.
      Cover page: The effect of pH, organic ligand chemistry and mineralogy on the sorption of beryllium over time
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2016)
        Cover page: The null hypothesis: globally steady rates of erosion, weathering fluxes and shelf sediment accumulation during Late Cenozoic mountain uplift and glaciation
        • Thesis
        • Peer Reviewed
        UC San Diego Electronic Theses and Dissertations (2020)

        The processes that shape Earth’s surface are constantly in flux. Continuous movements of soil and water and growth of ecosystems are what create the perfect stillness in Ansel Adam’s landscapes. In this dissertation, we investigate how a landscape responds to changes in the world around it. The tectonic uplift of Puerto Rico continues to shape the critical zone of the Luquillo Mountains today. We find that it has modified patterns of groundwater emergence, such that the river network is entrenching into ridgelines, in part, via the flux of groundwater. We demonstrate this with measurements of groundwater discharge and the grain size of the sediment it carries, compared to long-term channel incision rates derived with the cosmogenic radionuclide 10Be. Rock uplift enhances erosion rates, and a long-held belief in Earth Science is that soil production processes are linked and will respond to an enhanced erosive flux. By applying 10Be dating to measure soil production rates in the evolving landscape of the Luquillo Mountains, we determined that there is no such functional relationship. We re-evaluated the methods and assumptions that have been applied to this question elsewhere, and determined that in fact, soil production is independent of soil depth across the globe. This implies that no safety net will save us from the massive loss of soil due to anthropogenically accelerated erosion. Even outside of managed landscapes, accelerated erosion under climate change is an imminent possibility. We demonstrate this with a record of physical erosion over 26 ky recorded by 10Be concentrations in the layers of floodplain sediments. Erosion rates are greatly accelerated by the predominance of landsliding that occurs due to the onset of intense, frequent tropical storms in the Caribbean. The floodplain sediments contain a contemporaneous record of ecosystem dynamics in the δ13C isotope ratios of buried organic material. Similar to physical erosion in the watershed, ecological dynamics shift to a disturbance-dominated state due to coupling with a more volatile climate.

          Cover page: How a landscape responds to changes in the world around it: The Dynamic Critical Zone in the Luquillo Mountains, Puerto Rico
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2017)
          In many gravel-bedded rivers, floods that fill the channel banks create just enough shear stress to move the median-sized gravel particles on the bed surface (D50). Because this observation is common and is supported by theory, the coincidence of bankfull flow and the incipient motion of D50 has become a commonly used assumption. However, not all natural gravel channels actually conform to this simple relationship; some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport. We use a database of >300 gravel-bedded rivers and >600 10Be-derived erosion rates from across North America to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size ([Formula: see text]). We find that [Formula: see text] is significantly higher in West Coast river reaches (2.35, n = 96) than in river reaches elsewhere on the continent (1.03, n = 245). This pattern parallels patterns in erosion rates (and hence sediment supplies). Supporting our hypothesis, we find a significant correlation between upstream erosion rate and local [Formula: see text] at sites where this comparison is possible. Our analysis reveals a decrease in bed surface armoring with increasing [Formula: see text], suggesting channels accommodate changes in sediment supply through adjustments in bed surface grain size, as also shown through numerical modeling. Our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel bedded channels through its control on bed surface grain size.
            Cover page: Sediment supply controls equilibrium channel geometry in gravel rivers
            • Article
            • Peer Reviewed
            UC San Diego Previously Published Works (2017)
              Cover page: “Difference Dating”: A novel approach towards dating alpine glacial morainesCreative Commons 'BY-NC' version 4.0 license
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2016)
                Cover page: Relict landscape resistance to dissection by upstream migrating knickpoints
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2016)
                To measure the toxic potential of asbestos fibers-a known cause of asbestosis, lung cancer, and malignant mesothelioma-asbestos minerals are generally first ground down to small fibers, but it is unknown whether the grinding condition itself changes the fiber toxicity. To evaluate this, we ground chrysotile ore with or without water for 5-30 min and quantified asbestos-induced reactive oxygen species generation in elicited murine peritoneal macrophages as an indicator of fiber toxicity. The toxicity of dry-ground fibers was higher than the toxicity of wet-ground fibers. Grinding with or without water did not materially alter the mineralogical properties. However, dry-ground fibers contained at least 7 times more iron than wet-ground fibers. These results indicate that grinding methods significantly affect the surface concentration of iron, resulting in changes in fiber-induced reactive oxygen species generation or toxicity. Therefore, fiber preparation conditions should be accounted for when comparing the toxicity of asbestos fibers between reported studies.
                  Cover page: Asbestos Fiber Preparation Methods Affect Fiber Toxicity
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2015)
                  The modern Antarctic Dry Valleys are locked in a hyper-arid, polar climate that enables the East Antarctic Ice Sheet (EAIS) to remain stable, frozen to underlying bedrock. The duration of these dry, cold conditions is a critical prerequisite when modeling the long-term mass balance of the EAIS during past warm climates and is best examined using terrestrial paleoclimatic proxies. Unfortunately, deposits containing such proxies are extremely rare and often difficult to date. Here, we apply a unique dating approach to tundra deposits using concentrations of meteoric beryllium-10 ((10)Be) adhered to paleolake sediments from the Friis Hills, central Dry Valleys. We show that lake sediments were emplaced between 14-17.5 My and have remained untouched by meteoric waters since that time. Our results support the notion that the onset of Dry Valleys aridification occurred ~14 My, precluding the possibility of EAIS collapse during Pliocene warming events. Lake fossils indicate that >14 My ago the Dry Valleys hosted a moist tundra that flourished in elevated atmospheric CO2 (>400 ppm). Thus, Dry Valleys tundra deposits record regional climatic transitions that affect EAIS mass balance, and, in a global paleoclimatic context, these deposits demonstrate how warming induced by 400 ppm CO2 manifests at high latitudes.
                    Cover page: Extreme decay of meteoric beryllium-10 as a proxy for persistent aridity
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2015)
                      Cover page: Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed, Luquillo Mountains, Puerto Rico
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