Spatial and seasonal variations in the ecological characteristics of the free-living nematode assemblages in a large microtidal estuary

This study has determined the ways in which the density, number of species, species composition and trophic structure of free-living nematode assemblages in the subtidal waters of a large southern hemisphere microtidal estuary change spatially and seasonally, and has explored whether those four biotic characteristics are related to certain environmental factors. Based on data derived from samples collected seasonally at 12 sites throughout the estuary, the densities and number of species of nematodes decreased progressively with distance from estuary mouth, to reach a minimum at sites where salinities were most variable, and then increased slightly in the uppermost part of the estuary where salinities were least. Densities were also generally greatest in spring, due largely to increases in the abundance of epistrate-grazing species at this time and thus when the amount of primary food (microphytobenthos) peaked. The spatial distribution of the composition of the nematode assemblages was closely correlated with salinity and, to a lesser extent, grain-size composition and amount of particulate organic material (%POM) in the sediment. Although species composition changed sequentially along the estuary, the change was particularly pronounced between sites above and below the area where salinities started to decline markedly and become more variable and %POM increased markedly. This reflected, in particular, far greater abundances of Spirinia parasitifera at the six downstream sites and of Theristus sp. 1 at the six sites further upstream. Species composition underwent pronounced seasonal cyclical changes at all sites, presumably reflecting interspecific differences in the timing of peak reproduction and thus of recruitment. The trophic structure of the nematode assemblages changed both spatially and temporally in relation to the relative abundance of different food sources. Thus, for example, non-selective deposit feeders, such as Theristus sp. 1, dominated samples in the upper estuary, where %POM was by far the greatest, and was rare or absent at downstream sites. Conversely, epistrate grazers, such as species of the Chromadoridae, were most abundant at downstream sites in spring, when the density of the microphytobenthos reached its maximum.     

CORRELATES OF THE FUNCTIONAL STRUCTURE OF URBAN RETAIL AREAS: AN APPROACH EMPLOYING MULTIVARIATE ORDINATION

This paper considers the appropriateness of typologies of urban retailing areas based on multivariate functional data. The findings of a case study in which statistical and graphical methods were employed within the framework of multivariate ordination are presented. It is shown that the functional attributes of retail areas are closely associated with their location, accessibility, quality, morphology, size, period of development, and socioeconomic character.     

Kilometer-wave type III burst: Harmonic emission revealed by direction and time of arrival

A type III solar burst was observed at seven frequencies between 3.5 MHz and 80 kHz by the Michigan experiment aboard the IMP-6 satellite. From the data we can determine burst direction-of-arrival as well as time-of-arrival. We predict these quantities using simple models whose parameters we vary to obtain a good fit to the observations. We find that between 3.5 MHz and 230 kHz the observed radiation was emitted at the fundamental of the local plasma frequency while below 230 kHz it was emitted at the second harmonic. The exciter particles that produced the burst onset and burst peak have velocities of 0.27 and 0.12, respectively, in units of the velocity of light.     

Stokes imaging of the AM Her system ST LMi

The Stokes imaging technique of Potter, Hakala & Cropper is applied to the polarized emission from the AM Her system ST LMi. For the first time, the cyclotron emission region on the surface of the white dwarf is mapped in terms of optical depth/density in an analytical and objective manner. The region is found to consist of a less dense region leading a higher density region in orbital phase. It is demonstrated that the emission region needs to have a multi-temperature structure in order to explain the spectral slope and the general morphology of the cyclotron humps observed in the IR during the bright phase in ST LMi.
Furthermore, it is shown that a secondary emission region, fed by the same magnetic field lines that feed the main emission region, could be responsible for the positive circular polarization in the IR, the position angle variation and the excess flux during the faint phase of the white light observations which cannot be accounted for with a single emission region.     

Polarimetry and spectroscopy of RX J1141.3−6410: a single‐pole AM Her system

We present polarimetric and spectroscopic observations of the ROSAT source RX J1141.3−6410, recently identified as a polar. The detection of circular polarization variations, with an amplitude of 10 per cent, over a 3.16-h period confirms that the system is a polar (AM Herculis star). Supporting evidence comes from the nature of the emission lines and their radial velocity variability. In addition, we observe continuum slope changes in the far-red spectral region (∼6000–8200 Å), indicative of phase dependent cyclotron emission. Polarimetric modelling at two wavelengths establishes RX J1141.3−6410 as a single-pole system, with i ∼ β ∼70°. The accretion region is extended in magnetic longitude, and is totally self-occulted for ∼25 per cent of the orbit. The radial velocity curves derived from the emission lines show a phasing with maximum blueshift occurring with Δ φ ∼0.05 of maximum intensity and circular polarisation. In addition, the broader component of the lines exhibit a substantial radial velocity phase shift with respect to the narrower component, in the sense that the broad component preceeds the narrow. This can be readily understood if the narrower component is principally a result of orbital motion of the stream material and the broad component mainly a result of streaming motion near the coupling region. The phasing of the Ca  ii near-infrared line radial velocities also supports this general picture.     

Carbon fluxes in ecosystems of Yellowstone National Park predicted from remote sensing data and simulation modeling

Background

A simulation model based on remote sensing data for spatial vegetation properties has been used to estimate ecosystem carbon fluxes across Yellowstone National Park (YNP). The CASA (Carnegie Ames Stanford Approach) model was applied at a regional scale to estimate seasonal and annual carbon fluxes as net primary production (NPP) and soil respiration components. Predicted net ecosystem production (NEP) flux of CO₂ is estimated from the model for carbon sinks and sources over multi-year periods that varied in climate and (wildfire) disturbance histories. Monthly Enhanced Vegetation Index (EVI) image coverages from the NASA Moderate Resolution Imaging Spectroradiometer (MODIS) instrument (from 2000 to 2006) were direct inputs to the model. New map products have been added to CASA from airborne remote sensing of coarse woody debris (CWD) in areas burned by wildfires over the past two decades.

Results

Model results indicated that relatively cooler and wetter summer growing seasons were the most favorable for annual plant production and net ecosystem carbon gains in representative landscapes of YNP. When summed across vegetation class areas, the predominance of evergreen forest and shrubland (sagebrush) cover was evident, with these two classes together accounting for 88% of the total annual NPP flux of 2.5 Tg C yr^-1 (1 Tg = 10¹² g) for the entire Yellowstone study area from 2000-2006. Most vegetation classes were estimated as net ecosystem sinks of atmospheric CO₂ on annual basis, making the entire study area a moderate net sink of about +0.13 Tg C yr^-1. This average sink value for forested lands nonetheless masks the contribution of areas burned during the 1988 wildfires, which were estimated as net sources of CO₂ to the atmosphere, totaling to a NEP flux of -0.04 Tg C yr^-1 for the entire burned area. Several areas burned in the 1988 wildfires were estimated to be among the lowest in overall yearly NPP, namely the Hellroaring Fire, Mink Fire, and Falls Fire areas.

Conclusions

Rates of recovery for burned forest areas to pre-1988 biomass levels were estimated from a unique combination of remote sensing and CASA model predictions. Ecosystem production and carbon fluxes in the Greater Yellowstone Ecosystem (GYE) result from complex interactions between climate, forest age structure, and disturbance-recovery patterns of the landscape.     

Benthic macroinvertebrates as indicators of environmental deterioration in a large microtidal estuary

This study tested the hypothesis that, during recent years, the benthic macroinvertebrate fauna of the large basin of the Swan-Canning Estuary has changed in ways consistent with deteriorating environmental conditions in that estuary. Between 1986/7 and 2003/4, the compositions of that fauna altered markedly at the species and even family levels. Thus, the densities and number of species of molluscs, and especially of crustaceans, which are particularly susceptible to environmental stress, declined, while those of the more tolerant polychaetes increased. However, taxonomic distinctness declined consistently only at one of the four widely-spaced sampling sites and the dispersion of samples did not differ markedly between periods, indicating that the benthic fauna has not undergone such extreme changes as in the nearby Peel-Harvey Estuary. It is thus proposed that benthic macroinvertebrates can act as important indicators of the severity of environmental degradation in microtidal estuaries in regions where such perturbations are increasing.     

Can we improve the spatial predictions of seabed sediments? A case study of spatial interpolation of mud content across the southwest Australian margin

Spatially continuous data of environmental variables is often required for marine conservation and management. However, information for environmental variables is usually collected by point sampling, particularly for the marine region. Thus, methods generating such spatially continuous data by using point samples to estimate values for unknown locations become essential tools. Such methods are, however, often data- or even variable-specific and it is difficult to select an appropriate method for any given dataset. In this study, 14 methods (37 sub-methods) are compared using samples of mud content with five levels of sample density across the southwest Australian margin. Bathymetry, distance-to-coast, slope and geomorphic province were used as secondary variables. Ten-fold cross validation with relative mean absolute error (RMAE) and visual examination were used to assess the performance of these methods. A total of 1850 prediction datasets are produced and used to assess the performance of the methods and the effects of other factors considered. Considering both the accuracy and the visual examination, we found that a combined method (i.e., random forest and ordinary kriging: RKrf) is the most robust method. This method is novel, with a RMAE up to 17% less than that of the control. No threshold in sample density was detected in relation to prediction accuracy. No consistent patterns are observed between the performance of the methods and data variation. The RMAE of three most accurate methods is about 30% lower than that of the best methods in previous publications, highlighting the robustness of the methods selected in this study. The implications and limitations of this study are discussed and a number of suggestions are provided for further studies.     

COCORP: new perspectives on the deep crust

Summary. Relict sutures from colliding continents, regions characterized by a "young" Mono, layering and faulting throughout the crust, mid-crustal magma traps, and seismic "bright spots" which suggest deep crustal fluids are among recent COCORP findings. In addition, new studies of signal penetration, noise mitigation, recording geometry, and coherency filtering have yielded better understanding of, and substantial improvements in, data quality. Amplitude anomalies, or "bright spots", in the Basin and Range may be due to magma at mid-crustal levels; in one case, a normal fault appears to link the deep magma with young surface volcanics. Another bright spot. 15 km deep in southeastern Georgia, has a flat geometry that suggests a gas/liquid interface, perhaps within fluids underthrust along an Appalachian suture. The Mono continues to appear relatively undisturbed in many regions of past deformation, suggesting that its formation post-dates these major tectonic episodes. The diversity of reflection patterns from the U.S. Cordillera casts further doubt on the generality of the common model of a reflective, layered lower crust underlying a transparent upper crust.