Identification of resonances of an acoustically rigid sphere

Identification of resonances of an acoustically rigid sphere from simulated input-output data is presented. Scattering from the sphere is formulated using the classic Mie series and the singularity expansion method (SEM). A parametric inverse based on the SEM is discussed. The scattered velocity potential is divided into reflection, first creeping-wave, and second creeping-wave components. The effects on the identification of removing various components of the scattered potential are shown, along with the effects of adding small amounts of noise.     

S-type ignimbrites with polybaric crystallisation histories: the Tolmie Igneous Complex,Central Victoria,Australia

The Late Devonian Tolmie Igneous Complex (in north-eastern Victoria, Australia) contains S-type, intracaldera, rhyolitic ignimbrites with multiple generations of phenocrysts of biotite, garnet, cordierite and orthopyroxene; one unit also contains fayalitic olivine. Geothermometry and calculated phase relations indicate high-T deep- to mid-crustal origins for the magmas, with crystallisation at several levels. At least four separate magma groups make up the complex. Compositional variations within and between ignimbrites are adequately modelled by selective entrainment of peritectic garnet, ilmenite, orthopyroxene and plagioclase into the magmas. Neither crystal fractionation nor mafic-felsic magma mixing played a role. Chemical and isotope data suggest that the magma sources were once variably Ba-enriched arc greywackes with different proportions of clay. The deep origin of some of the Tolmie Complex magmas means that supracrustal rocks underlie parts of north-eastern Victoria at depths of around 35 km. This has important implications for understanding the region’s tectonic development.     

Stream Temperature Modeling and Fiber Optic Temperature Sensing to Characterize Groundwater Discharge

The Ngongotaha Stream was used as a case study to assess the applicability of fiber optic distributed temperature sensing (FODTS) to identify the location of springs and quantify their discharge. Thirteen springs were identified, mostly located within a 115 m reach, five discharged from the right bank and eight from the left bank. To quantify groundwater discharge, a new approach was developed in which the one-dimensional transient heat transport model was fitted to the FODTS measurements, where the main calibration parameters of interest were the unknown spring discharges. The spatial disposition of the groundwater discharge estimation problem was constrained by two sources of information; first, the stream gains ∼500 L/s as determined by streamflow gauging. Second, the temperature profiles of the left and right banks provide the spatial disposition of springs and their relative discharges. FODTS was used to measure stream temperature near the left and right banks, which created two temperature datasets. A weighted average of the two datasets was then calculated, where the weights reflected the degree of mixing between the right and left banks downstream of a spring. The new approach in this study marks a departure from previous studies, in which the general approach was to use the steady-state thermal mixing model (Selker et al. 2006a; Westhoff et al. 2007; Briggs et al. 2012) to infer groundwater discharge, which is then used as an input into a transient model of the general form of equation to simulate stream temperature (Westhoff et al. 2007).     

Updating estimates of low-streamflow statistics to account for possible trends

ABSTRACT

Accurate estimators of streamflow statistics are critical to the design, planning, and management of water resources. Given increasing evidence of trends in low-streamflow, new approaches to estimating low-streamflow statistics are needed. Here we investigate simple approaches to select a recent subset of the low-flow record to update the commonly used statistic of 7Q10, the annual minimum 7-day streamflow exceeded in 9 out of 10 years on average. Informed by low-streamflow records at 174 US Geological Survey streamgages, Monte Carlo simulation experiments evaluate competing approaches. We find that a strategy which estimates 7Q10 using the most recent 30 years of record when a trend is detected, reduces error and bias in 7Q10 estimators compared to use of the full record. This simple rule-based approach has potential as the basis for a framework for updating frequency-based statistics in the context of possible trends.     

How hydroperiod and species richness affect the balance of resource flows across aquatic-terrestrial habitats

Ecosystem functioning is influenced by the flow of nutrients, detritus, and organisms. Variation in these flows, like that found in temporary ecosystems, affects temporal and spatial patterns of community diversity and secondary production. We evaluated the influence of hydroperiod and ecosystem size on the bi-directional flow of subsidies from intermittent ponds and surrounding forests by quantifying litter deposition and the abundance and biomass of emerging insects and amphibians. In addition, we assessed whether amphibian and insect diversity influenced the magnitude of cross-habitat resource flux. We found substantial spatial and temporal variation in the magnitude, composition, and timing of cross-habitat resource subsidies. Overall, deposition into ponds far exceeded biomass exported via insect and amphibian emergence. We found a negative association between resource flux and the diversity of amphibians and insects. Different species groups contributed to flux patterns unequally, with insects having higher diversity but lower flux compared to amphibians. Organismal flux varied among ponds with amphibians having the highest flux in the shortest hydroperiod pond and insect flux was highest from an intermediate hydroperiod pond. This work reveals how variation in pond size and permanence affects species diversity and ecosystem flows. Species composition played a major role in flux differences across ponds. Further, given the general lack of research and conservation prioritization of temporary ponds, uncovering how these ponds contribute to cross-habitat linkages is necessary to develop fully integrated management strategies.