Little Arnot Run: An Evaluation of Groundwater-Surface Water Interactions with Regard to Hyporheic Exchange and Temperature
Little Arnot Run is a second-order stream in the Allegheny National Forest, Pennsylvania. In many areas the stream was dredged, straightened, and converted to a narrow, deep, single-thread channel, which continues to be disconnected from the floodplain. This project is part of a larger stream restoration study by the United States Forest Service (USFS) and Bucknell University currently underway working to characterize the factors controlling geomorphic processes operating within the watershed in order to direct restoration activities set to take place later in the year. Preliminary analysis of groundwater piezometers, stream temperature gage station data, and weather station data suggests significant hyporheic exchange to the channel. The current assessment of both shallow and alluvial aquifers as well as in deeper sections of the stream is being done in order to quantify groundwater-surface water exchange and potential for reconnecting abandoned side channels and vernal pools on the floodplain.

Effect of Self-Oxidation on Deposited Cigarette Smoke Composition and Third-Hand Smoke

While the implications of first-hand and second-hand tobacco smoke have been thoroughly studied, much less is known about the effects of so-called ‘third-hand smoke’ (THS) on the environment and human health. THS is a collection of chemicals from cigarette smoke that adhere to indoor surfaces (e.g., walls, flooring, furniture, clothing) and extend the exposure risks for bystanders. As THS chemicals stay on surfaces for long periods of time, we hypothesize that reactions between chemicals within the deposited THS film, with previously deposited materials, and with the surface itself may be occurring. In this study, the mechanisms and rates of the former two categories of reactions were probed. Cigarette smoke was collected on glass surfaces and incubated under fluorescent lighting for various periods of time, revealing changes in the chemical composition. The rates of chemical removal and product formation were determined. Notably, experimental data has indicated a decrease in nicotine concentrations and an increase in nicotine oxide concentrations over time, signifying that nicotine was removed by oxidation reactions occurring within THS films. Further experiments were conducted in which cigarette smoke was collected on glass surfaces that were pre-coated with chemical scavengers to help identify oxidant species that affect the composition of THS films. Future studies will look to include a variety of deposited films, different reactive substrate materials, and other environmental factors in order to obtain a better understanding about what goes on after the cigarette goes out.

U-Pb Isotope Dating of Monazite from the Sierra Estrella Mountains of Arizona: Evidence for ca. 1.4 Billion Year Old Metamorphism and Deformation.

U-Pb isotope dating of monazite from the Sierra Estrella mountains near Phoenix, Arizona, yield metamorphic ages between about 1.42 and 1.40 billion years old (b.y.o.). These ages suggest that the high temperature and high pressure metamorphism (T = 800 °C, P = 9 kbar) experienced by these rocks was associated with the 1.50 to 1.35 b.y.o. Picuris Orogeny. About 20 samples were collected from the Sierra Estrella mountains. Four samples were selected for U-Pb analyses of monazite, a rare earth element phosphate mineral (REE(PO4)). Monazite gains were identified and imaged using the scanning electron microscope in the Department of Geology, Bucknell University. U-Pb analyses of monazite were conducted at the University of New Brunswick using Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Two samples from the north end of the mountain range (CD20-03Ba and CD20-07Bb) yield concordia ages of 1.400 ± .005 b.y.o (n= 8, MSWD = 0.13) and 1.410 ± 0.004 b.y.o. (n = 8, MSWD = 0.25), respectively. Two samples from about 20 km to the south (CD20-09 and CD20-14b) yield concordia ages of 1.410 ± 0.01 b.y.o. (n=8, MSWD = 0.74) and 1.420 +/- 0.006 b.y.o. (n = 8, MSWD = 0.18), respectively. Our new U-Pb ages are similar to 1.420-1.380 b.y.o. monazite previously reported in New Mexico that are also attributed to the Picuris Orogeny.

Estimating the Pressure and Temperature of Metamorphism of ca. 1.4 Ga Metapelitic Rocks from the Sierra Estrella Range, Phoenix, Arizona USA

Meijer (2019) reported what is likely the first known occurrence of Mesoproterozoic granulite facies rocks in Arizona. However, the temperatures and pressures of metamorphism are unknown. To better constrain the conditions of metamorphism, metapelitic rocks were collected from the north end of the Sierra Estrella mountain range and are characterized by Grt-Bt-Pl-Qtz-Ky-Sil with significant retrograde Ms-Chl-Ep, and Grt-Bt-Pl-Qtz-Ky-Sil-Kfs with very little retrograde overprint.
Preliminary thermodynamic modeling of these two samples was performed with Theriak–Domino and the H&P ’98 data set. The Sil inclusions within Grt suggest Sil growth possibly during subsolidus St-breakdown or Ms-melting in both samples. The presence of Ky bearing melt textures in both samples may reflect prograde growth of Ky from Ms- or Bt-melting suggesting minimum P¬–T conditions > 7.5 kbar and > 700 °C. A significant amount of retrograde Ms in sample implies in-situ melt crystallization during retrograde cooling.
To further constrain pressures of metamorphism, Raman spectroscopy was employed to measure peak positions of quartz inclusions in garnet (QuiG). The results of this work show peak shifts ranging from 0 to -0.1 cm-1. This equates to metamorphic pressures of 8-9 kbar at about 750-800 °C.
Previously reported zircon ages for the area suggest partial melting near 1.4 Ga (Meijer, 2019). The timing and P-T conditions of metamorphism in the Sierra Estrella mountains are similar to high-grade metamorphic rocks in northern New Mexico and southern Colorado; these rocks likely represent the southwestern extension of the Picuris orogenic belt.

Visual Characterization of Aponeurosis Microstructure

Aponeurosis is a tendinous sheath-like tissue found in many muscle-tendon units, and the muscle-aponeurosis junction is poorly understood. We want to determine the structure of the transition from muscle to aponeurosis and how it may be similar or different from the myotendinous junction. Imaging and visually characterizing the muscle-aponeurosis junction using SEM imaging of tissue samples will show how the tendon and muscle fibers interact with one another in the transition zone. It has been observed that there is a non-uniform strain placed on the aponeurosis, and so imaging of the tissue will reveal how force affects the alignment of the collagen fibers found in aponeurosis tissue. Examining how the waviness of collagen fibers changes as the tissue is placed under force will allow for better understanding of the material and structural properties of aponeurosis tissue. Evaluating these characteristics will help us better understand how damages to the tissues occur, how those damages can be repaired and rehabilitated, and how to properly develop computer models of the musculoskeletal system. Sample images using the SEM have been taken to develop a general understanding of aponeurosis morphology.

Noise-driven aggregation of swimmers in the Kolmogorov flow

We investigate theoretically the dynamics of ellipsoidal microswimmers in an externally imposed, laminar Kolmogorov flow. Through a phase-space analysis of the dynamics without noise, we find that swimmers favor either cross-stream or rotational drift, depending on their swimming speed and aspect ratio. When including noise, i.e. rotational diffusion, Langevin simulations of our model show a transition from swimmer aggregation in low-shear regions of the flow to aggregation in high-shear regions as the parameters are varied. We find that rotational diffusion tends to drive swimmers into certain parts of phase space. We characterize the dependence of this noise-driven phase-space aggregation on a swimmer’s speed, aspect ratio, and rotational diffusivity. The properties of the swimmer trajectories with noise explain the transition from high-shear to low-shear aggregation.

*Support from NSF Grants: DMR- 1806355 and CMMI-1825379.

How to Code a Simulation with LAMMPS

We discuss how to use the computer program LAMMPS to build and run a molecular dynamics computer simulation. We provide general steps in designing the simulation, with examples along the way from our summer research project modelling granular media.

Evaluating the Impact of Stream Restoration Techniques on Bank Erosion, Stream Morphology, and Soil Carbon at an Unnamed Tributary of Pine Creek near Woodward, central Pennsylvania

Live staking is a stream restoration technique in which live cuttings and stems taken from native species of trees and shrubs are placed into stream banks, eventually growing into new plants which aids in riverbank protection by increasing soil cohesion. Live staking is an economically viable and easy technique for stream restoration that is being widely implemented in the Chesapeake Bay watershed. Because of the growing use of live staking in stream restorations, there is a growing need for research on the link between live staking and geomorphic resiliency. Here we investigate the impact of live staking on bank erosion, stream morphology, and soil carbon at an unnamed tributary of Pine Creek near Woodward, Pennsylvania. Restoration efforts of this tributary began in fall 2018 by the Penn’s Valley Conservation Association (PVCA) and live staking began in spring 2019 in the upstream section of the tributary.

In this study, we collected baseline data for a long-term study of the impact of live stakes on the floodplain and channel geomorphology, and we investigated the baseline soil carbon distribution. To do this, we mapped floodplain and channel topography and surveyed the stream channel using a Trimble RTK GPS unit. Floodplain soils were sampled along nine transects perpendicular to the channel to investigate soil properties and measure the spatial distribution of soil carbon (using a CHN analyzer). Results from stream channel surveying indicate undercut banks, channelization, very low stream velocity, and silt and clay on the stream bed. Throughout the field site, the soils are silty loams with thin O-horizons (2-8 cm) and some local variability within transects. Soil carbon analysis shows carbon values between 0.36% and 3.32%, which is low within the expected range of soil carbon for degraded floodplain soils. Although we did not observe significant spatial patterns in soil characteristics or in soil carbon content, we did document small increases in soil carbon near the channel, and high amounts of soil carbon near a protected wetland area. We predict that in future years, as the live stakes vegetate the stream banks at this site, there will be an increase in soil carbon, changes in stream bed character and channel sinuosity, and more soil variability, including a thicker O-horizon and possible changes in grain size.