Organic carbon storage in mountain river valley bottoms of the western United States

2018 Summer.Includes bibliographical references.Valley bottoms, which include river channels and associated floodplains, are important components of the terrestrial carbon sink. Downed wood and floodplain soil in valley bottoms act as transient pools of organic carbon (OC) that can be stored for up to millennial timescales. This dissertation focuses on quantifying OC storage as downed wood and soil in mountain river valley bottoms in four disparate watersheds that span three mountain ranges across the western United States. Across these four basins, I measured wood load, floodplain OC content, morphologic metrics, and/or vegetation metrics at a total of 178 sites. I find that wood load is a function of metrics that relate to river corridor spatial heterogeneity and wood storage patterns (together determining wood trapping efficiency) at the reach scale and, at a broader spatial scale, wood supply. Wood in an undisturbed basin stores twice as much wood OC as a similar but extensively clearcut basin. In examining floodplain soil OC, I find that much of the variability in OC concentration is due to local factors, such as soil moisture, elevation (a proxy for temperature), and valley bottom geometry. From this, I conclude that local factors likely play a dominant role in regulating OC concentration in valley bottoms, and that inter-basin trends in climate or vegetation characteristics may not translate directly to trends in OC storage. I also use analysis of OC concentration and soil texture by depth to infer that OC is input to floodplain soils mainly by decaying vegetation, not overbank deposition of fine, OC-bearing sediment. Valley bottoms store significant OC stocks in floodplain soil and downed wood (ranging from 0 to 998 Mg C/ha) that vary with valley bottom form and geomorphic processes. Valley bottom morphology, soil retention, and vegetation dynamics determine partitioning of valley bottom OC between soil and wood, implying that modern biogeomorphic process and the legacy of past erosion regulate the modern distribution of OC in river networks. Soil burial is essential to preserving old OC, as measured by an extensive sample of 121 radiocarbon ages of floodplain soil OC. These radiocarbon data indicate a median residence time of floodplain soil OC of 185 yr BP. The age of the floodplain soil OC pool and the distribution of OC between wood and soil imply that OC storage in mountain rivers is sensitive over relatively short timescales to alterations in soil and wood retention, which may have both short- and long-term feedbacks with the distribution of OC between the land and atmosphere. Mountain river valley bottoms act as a high magnitude and moderately long-lasting pool of OC stored on land

A microrod-resonator Brillouin laser with 240 Hz absolute linewidth

We demonstrate an ultralow-noise microrod-resonator based laser that oscillates on the gain supplied by the stimulated Brillouin scattering optical nonlinearity. Microresonator Brillouin lasers are known to offer an outstanding frequency noise floor, which is limited by fundamental thermal fluctuations. Here, we show experimental evidence that thermal effects also dominate the close-to-carrier frequency fluctuations. The 6-mm diameter microrod resonator used in our experiments has a large optical mode area of ~100 {\mu}m$^2$, and hence its 10 ms thermal time constant filters the close-to-carrier optical frequency noise. The result is an absolute laser linewidth of 240 Hz with a corresponding white-frequency noise floor of 0.1 Hz$^2$/Hz. We explain the steady-state performance of this laser by measurements of its operation state and of its mode detuning and lineshape. Our results highlight a mechanism for noise that is common to many microresonator devices due to the inherent coupling between intracavity power and mode frequency. We demonstrate the ability to reduce this noise through a feedback loop that stabilizes the intracavity power.Comment: 11 pages, 5 figure

Notes on Hierarchies and Inductive Inference

The following notes rework a discussion due to Kevin Kelly on the application of topological notions in the context of learning (see Kelly (1990)). All the results except for (2), (4) and (9) are due to Kelly, but are proved differently

Relevant Consequence and Empirical Inquiry

A criterion of adequacy is proposed for theories of relevant consequence. According to the criterion, scientists whose deductive reasoning is limited to some proposed subset of the standard consequence relation must not thereby suffer a reduction in scientific competence. A simple theory of relevant consequence is introduced and shown to satisfy the criterion with respect to a formally defined paradigm of empirical inquiry

Synthesizing inductive expertise

AbstractWe consider programs that accept descriptions of inductive inference problems and return machines that solve them. Several design specifications for synthesizers of this kind are considered from a recursion-theoretic perspective

Uniform Inductive Improvement

We examine uniform procedures for improving the scientific competence of inductive inference machines. Formally, such procedures are construed as recursive operators. Several senses of improvement are considered, including (a) enlarging the class of functions on which success is certain, and (b) transforming probable success into certain success

Logic and Learning

The theory of first-order logic - or Model Theory - appears in few studies of learning and scientific discovery. We speculate about the reasons for this omission, and then argue for the utility of Model Theory in the analysis and design of automated systems of scientific discovery. One scientific task is treated from this perspective in detail, namely, concept discovery. Two formal paradigms bearing on this probleni are presented and investigated using the tools of logical theory. One paradigm bears on PAC learning, the other on identification in the limit

A Universal Inductive Inference Machine

A paradigm of scientific discovery is defined within a first-order logical framework. It is shown that within this paradigm there exists a formal scientist that is Turing computable and universal in the sense that it solves every problem that any scientist can solve. It is also shown that universal scientists exist for no regular logics that extend first order logic and satisfy the Lowenheim-Skolem condition