Consumer-Driven Nutrient Recycling in Arctic Alaskan Lakes: Controls, Importance for Primary Productivity, and Influence on Nutirient Limitation

In lakes, fish and zooplankton can be both sources and sinks of nitrogen (N) and phosphorus (P) through the consumption of organic N and P, and subsequent excretion of bioavailable inorganic forms. These source/sink dynamics, known as consumer-driven nutrient recycling (CNR), may, in turn, control the availability of potentially limiting nutrients for algal primary production. In this dissertation I investigate the importance and controls of CNR as a source of inorganic N and P for primary production (Chapter 2). I then examine zooplankton CNR as a mechanism for increasing nutrient mean resident time (MRT) in the mixed layer of lakes (Chapter 3). Finally, I assess whether zooplankton communities dominated by different taxa can affect N versus P deficient conditions for phytoplankton production through differential N and P recycling rates (Chapter 4). Direct excretion of N and P by fish communities was modest in arctic lakes, and accounted for \u3c 4 % of the N and P required for primary production. Recycling of N and P by zooplankton communities was relatively high, and the fraction of algal N and P demand supplied by zooplankton CNR ranged from 4 - 90% for N and 7 - 107% for P. MRT of 15N, measured in the mixed layer of an arctic lake, was ~16 days, compared to 14 days predicted by a ecosystem model simulation with zooplankton N recycling and 8 days in a model simulation where zooplankton N recycling was absent. The 75% increase in N MRT between model simulations with and without zooplankton recycling suggests that zooplankton N recycling is an important mechanism for retaining N in lake ecosystems. I observed relatively high negative correlations between precipitation and phytoplankton N (r = -0.33) and P (r = -0.30) deficiencies. I also observed a significant positive correlation (r = 0.42, p = 0.03) between zooplankton communities with higher copepod biomass, relative to cladoceran biomass, and phytoplankton N-deficient conditions. These results suggest that when precipitation is high N and P deficiency is low in the phytoplankton. When precipitation is low, however, zooplankton communities composed primarily of copepods contribute to N-deficient conditions for phytoplankton production

Imaging Thermal Stratigraphy in Freshwater Lakes Using Georadar

Thermal stratification exerts significant control over biogeochemical processing in freshwater lakes. Thus, the temporal and spatial distribution of the thermal structure is an important component in understanding lake ecosystems. We present the first reported observations of lake thermal stratification from surface based georadar measurements acquired over two small freshwater lakes. This method is very useful because it can provide rapid acquisition of 2D or 3D lotic stratification

Exploring and Testing Wildfire Risk Decision-Making in the Face of Deep Uncertainty

We integrated a mechanistic wildfire simulation system with an agent-based landscape change model to investigate the feedbacks among climate change, population growth, development, landowner decision-making, vegetative succession, and wildfire. Our goal was to develop an adaptable simulation platform for anticipating risk-mitigation tradeoffs in a fire-prone wildland– urban interface (WUI) facing conditions outside the bounds of experience. We describe how five social and ecological system (SES) submodels interact over time and space to generate highly variable alternative futures even within the same scenario as stochastic elements in simulated wildfire, succession, and landowner decisions create large sets of unique, path-dependent futures for analysis. We applied the modeling system to an 815 km2 study area in western Oregon at a sub-taxlot parcel grain and annual timestep, generating hundreds of alternative futures for 2007–2056 (50 years) to explore how WUI communities facing compound risks from increasing wildfire and expanding periurban development can situate and assess alternative risk management approaches in their localized SES context. The ability to link trends and uncertainties across many futures to processes and events that unfold in individual futures is central to the modeling system. By contrasting selected alternative futures, we illustrate how assessing simulated feedbacks between wildfire and other SES processes can identify tradeoffs and leverage points in fire-prone WUI landscapes. Assessments include a detailed “post-mortem” of a rare, extreme wildfire event, and uncovered, unexpected stabilizing feedbacks from treatment costs that reduced the effectiveness of agent responses to signs of increasing risk

Nanostructured Oxygen Sensor - Using Micelles to Incorporate a Hydrophobic Platinum Porphyrin

Hydrophobic platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP) was physically incorporated into micelles formed from poly(ε-caprolactone)-block-poly(ethylene glycol) to enable the application of PtTFPP in aqueous solution. Micelles were characterized using dynamic light scattering (DLS) and atomic force microscopy (AFM) to show an average diameter of about 140 nm. PtTFPP showed higher quantum efficiency in micellar solution than in tetrahydrofuran (THF) and dichloromethane (CH2Cl2). PtTFPP in micelles also exhibited higher photostability than that of PtTFPP suspended in water. PtTFPP in micelles exhibited good oxygen sensitivity and response time. This study provided an efficient approach to enable the application of hydrophobic oxygen sensors in a biological environment

Relationships between lake transparency, thermocline depth, and sediment oxygen demand in Arctic lakes

The burial of organic matter within lake sediments can be a significant component of landscape carbon cycling. Whether organic matter deposited in lake sediments is sequestered or mineralized depends on factors limiting the decomposition rate of organic matter, such as temperature and the availability of oxygen. In stratified lakes, the distribution of temperature and oxygen is determined by the depth of the thermocline, and therefore sediment organic matter burial should be sensitive to changes in thermocline depth. Using a survey of more than 30 lakes over 3 years in the Alaskan Arctic, we found that thermocline depth during the summer was positively correlated with water transparency. Furthermore, using sediment incubations from 3 lakes, we found that variation in sediment oxygen demand is primarily affected by variation in temperature and the availability of oxygen with limited effect of the source of the sediments. Because variation in temperature and oxygen concentration in stratified lakes is mainly determined by the depth of thermocline, these results indicate that changes in transparency can have indirect effects on the rate of organic matter mineralization in lakes. A reduction in thermocline depth that results from decreased lake transparency may decrease the breakdown of sediment organic matter and increase the storage of organic carbon in lake sediments

Heart Rate Responses during Simulated Fire Ground Scenarios among Full-Time Firefighters

International Journal of Exercise Science 13(2): 374-382, 2020. Simulated fire ground scenarios (SFGS) provide firefighters with an opportunity to maintain skills, receive feedback, and optimize performance. Although there is extensive research on heart rate (HR) changes in the firefighter population, few examine the differences between positions. Firefighters are primarily responsible for fire suppression and control (23), officers for emergency operations and organizational management, paramedics for providing on-scene emergency medical care, and drivers are responsible for driving the fire apparatus. Utilizing HR analysis to quantify the physical demands of SFGS among firefighting crews by position. Sixty-seven male (age: 38.97 ± 9.17; ht: 177.99 ± 6.45 cm. wt: 88.83 ± 13.55 kg) firefighters (FF) participated in this investigation. FF crews performed two SFGS involving the suppression and control of a structural fire. Participants were outfitted with heart rate (HR) monitors and average heart rate (HRavg) and maximum heart rate (HRmax) data were collected for each of the two SFGS. Significant differences were observed for Age (P = 0.01), APMHR (P = 0.01), HRmax1(P = 0.04), and HRmax2(P = 0.04) in which firefighters had higher values for Age-predicted maximal heart rate (APMHR), HRmax1, HRmax2compared to the officers. SFGS can be very physically demanding events that may elicit maximal or near maximal HR responses regardless of position. Based on the metabolic demands of these events and the individual firefighter’s capabilities, this information can be used to develop resistance training and conditioning programs that optimize performance at maximal or near maximal heart rates

A Substellar Companion to a Hot Star in K2's Campaign 0 Field

The K2 mission has enabled searches for transits in crowded stellar environments very different from the original Kepler mission field. We describe here the reduction and analysis of time series data from K2's Campaign 0 superstamp, which contains the 150 Myr open cluster M35. We report on the identification of a substellar transiting object orbiting an A star at the periphery of the superstamp. To investigate this transiting source, we performed ground based follow-up observations, including photometry with the Las Cumbres Observatory telescope network and high resolution spectroscopy with Keck/High Resolution Echelle Spectrometer. We confirm that the host star is a hot, rapidly rotating star, precluding precision radial velocity measurements. We nevertheless present a statistical validation of the planet or brown dwarf candidate using speckle interferometry from the WIYN telescope to rule out false positive stellar eclipsing binary scenarios. Based on parallax and proper motion data from Gaia Data Release 2 (DR2), we conclude that the star is not likely to be a member of M35, but instead is a background star around 100 pc behind the cluster. We present an updated ephemeris to enable future transit observations. We note that this is a rare system as a hot host star with a substellar companion. It has a high potential for future follow-up, including Doppler tomography and mid-infrared secondary transit observations

The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module

The Simons Observatory (SO) includes four telescopes that will measure the temperature and polarization of the cosmic microwave background using over 60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES bolometers are read out by a microwave RF SQUID multiplexing system with a multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to magnetic field pickup and that it is hard to predict how they will respond to such fields, it is important to characterize the magnetic response of these systems empirically. This information can then be used to limit spurious signals by informing magnetic shielding designs for the detectors and readout. This paper focuses on measurements of magnetic pickup with different magnetic shielding configurations for the SO universal multiplexing module (UMM), which contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic pickup of a prototype UMM was tested under three shielding configurations: no shielding (copper packaging), aluminum packaging for the UMM, and a tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold stage. The measurements show that the aluminum packaging outperforms the copper packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K shield further increases the relative shielding factor in the aluminum configuration by 1-2 orders of magnitude.Comment: 7 pages, 4 figure, conference proceedings submitted to the Journal of Low Temperature Physic