Soluble organic and inorganic nutrient fluxes in clearcut and mature deciduous forests

ABSTRACT The mechanisms by which forest ecosystems retain or lose soluble inorganic nutrients after disturbance are well known, but substantial amounts of soluble organic nutrients may also be released from cut vegetation. Our objective was to compare the leaching of dissolved organic and inorganic nutrients in cut and mature forest stands and to develop hypotheses about factors controlling the retention of soluble organic nutrients after disturbance. Solution chemistry was measured for 2 yr after clearcutting a small area in the surrounding undisturbed deciduous forest on a reference watershed at the Coweeta Hydrologic Laboratory in the Appalachian Mountains. Concentrations of dissolved organic C (DOC) and N (DON) in slash leachate were 2.6 to 3.2 times the concentrations in throughfall from undisturbed forest Concentrations in forest floor, A horizon, and B horizon solutions from cut plots were 1.2 to 3.8 times those from undisturbed forest. Dissolved organic P (DOP) concentrations in cut plots were 3.1 and 3.6 times those of uncut plots in solutions from slash and forest floor, respectively, but did not differ in mineral soil. Fluxes of DOC, DON, and DOP in all strata were greater in cut plots than uncut plots. Fluxes of DON were greater than those of ammonium plus nitrate N in all strata of both cut and uncut plots. We hypothesize that the wellrecognized retention mechanisms for inorganic nutrients combine with equilibrium adsorption of dissolved organic matter to efficiently buffer against leaching of both soluble inorganic and organic nutrients after clearcutting

Measurement of F 17 (d,n) Ne 18 and the impact on the F 17 (p,γ) Ne 18 reaction rate for astrophysics

Background: The F17(p,γ)Ne18 reaction is part of the astrophysical hot CNO cycles that are important in astrophysical environments like novas. Its thermal reaction rate is low owing to the relatively high energy of the resonances and therefore is dominated by direct, nonresonant capture in stellar environments at temperatures below 0.4 GK. Purpose: An experimental method is established to extract the proton strength to bound and unbound states in experiments with radioactive ion beams and to determine the parameters of direct and resonant capture in the F17(p,γ)Ne18 reaction. Method: The F17(d,n)Ne18 reaction is measured in inverse kinematics using a beam of the short-lived isotope F17 and a compact setup of neutron, proton, γ-ray, and heavy-ion detectors called resoneut. Results: The spectroscopic factors for the lowest l=0 proton resonances at Ec.m.=0.60 and 1.17 MeV are determined, yielding results consistent within 1.4σ of previous proton elastic-scattering measurements. The asymptotic normalization coefficients of the bound 21+ and 22+ states in Ne18 are determined and the resulting direct-capture reaction rates are extracted. Conclusions: The direct-capture component of the F17(p,γ)Ne18 reaction is determined for the first time from experimental data on Ne18

Experimental Investigation of the Ne 19 (p,γ)20Na Reaction Rate and Implications for Breakout from the Hot CNO Cycle

The Ne19(p,γ)Na20 reaction is the second step of a reaction chain which breaks out from the hot CNO cycle, following the O15(α,γ)Ne19 reaction at the onset of x-ray burst events. We investigate the spectrum of the lowest proton-unbound states in Na20 in an effort to resolve contradictions in spin-parity assignments and extract reliable information about the thermal reaction rate. The proton-transfer reaction Ne19(d,n)Na20 is measured with a beam of the radioactive isotope Ne19 at an energy around the Coulomb barrier and in inverse kinematics. We observe three proton resonances with the Ne19 ground state, at 0.44, 0.66, and 0.82 MeV c.m. energies, which are assigned 3+, 1+, and (0+), respectively. In addition, we identify two resonances with the first excited state in Ne19, one at 0.20 MeV and one, tentatively, at 0.54 MeV. These observations allow us for the first time to experimentally quantify the astrophysical reaction rate on an excited nuclear state. Our experiment shows an efficient path for thermal proton capture in Ne19(p,γ)Na20, which proceeds through ground state and excited-state capture in almost equal parts and eliminates the possibility for this reaction to create a bottleneck in the breakout from the hot CNO cycle

Teaching After Retirement

Having enjoyed teaching during my active career, I continued to teach summer school following retirement. Self-observed sensory and cognitive impairments, although not mentioned by students in their evaluations, induced me to consider the pros and cons of continuing to teach. My hope is that this list of benefits and problems will be of assistance to other instructors approaching retirement. © 2014, SAGE Publications. All rights reserved

Autonomous Aerial Observations To Extend And Complement The Earth Observing System: A Science Driven, Systems Oriented Approach

The current Earth observing capability depends primarily on spacecraft missions and ground-based networks to provide the critical on-going observations necessary for improved understanding of the Earth system. Aircraft missions play an important role in process studies but are limited to relatively short-duration flights. Suborbital observations have contributed to global environmental knowledge by providing in-depth, high-resolution observations that space-based and in-situ systems are challenged to provide; however, the limitations of aerial platforms - e.g., limited observing envelope, restrictions associated with crew safety and high cost of operations have restricted the suborbital program to a supporting role. For over a decade, it has been recognized that autonomous aerial observations could potentially be important. Advances in several technologies now enable autonomous aerial observation systems (AAOS) that can provide fundamentally new observational capability for Earth science and applications and thus lead scientists and engineers to rethink how suborbital assets can best contribute to Earth system science. Properly developed and integrated, these technologies will enable new Earth science and operational mission scenarios with long term persistence, higher-spatial and higher-temporal resolution at lower cost than space or ground based approaches. This paper presents the results of a science driven, systems oriented study of broad Earth science measurement needs. These needs identify aerial mission scenarios that complement and extend the current Earth Observing System. These aerial missions are analogous to space missions in their complexity and potential for providing significant data sets for Earth scientists. Mission classes are identified and presented based on science driven measurement needs in atmospheric, ocean and land studies. Also presented is a nominal concept of operations for an AAOS: an innovative set of suborbital assets that complements and augments current and planned space-based observing systems