Towards improving ambient noise tomography using simultaneously curvelet denoising filters and SEM simulations of seismic ambient noise

The aim of this article is to investigate a possible way to improve ambient noise tomography by expanding the data base of useful cross-correlation measurements. We show that the curvelet transform makes it possible to compute synthetic noise correlations by simulating directly seismic ambient noise using the spectral element method. These synthetic correlations can in turn be used to identify surface waves and overtones even on correlations having a signal to noise ratio much lower than one. We hope that the possibility to compute SEM synthetic correlations and to extract more information from correlations will be useful to improve ambient noise tomography and monitoring.     

Shifts in an epibenthic trophic web across a marine frontal area in the Southwestern Atlantic (Argentina)

Marine benthic trophic relationships and food web structures may be influenced by benthic–pelagic coupling processes, which could also be intensified by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ¹³C and δ¹⁵N) analysis to investigate the influence of the Southwest (SW) Atlantic shelf-break front (SBF; 38–39°S, 55–56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~ 100 m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were inferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ¹³C), and those of the sea urchin, Sterechinus agassizi (δ¹⁵N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ¹³C-enriched and δ¹⁵N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ¹³C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ¹⁵N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities.     

Seeing the forest for the trees: Local-level resource use and forest restitution in postsocialist Bulgaria

Recent legislation for the restitution of ownership rights to, and subsequent management of, formerly privately owned forests in postsocialist Bulgaria has focused largely albeit not exclusively on the restored forests from the perspective of timber production, that is, `forest' equals `harvestable timber resource'. Using ethnographic data collected in rural Rhodope Mountain communities, this paper presents a local-level perspective on forests and forest use, including the meaning that forests hold for local residents as a source of non-timber forest products such as mushrooms and medicinal plants, of animal pasture, and of firewood for household heating and cooking. This local social perspective is then contrasted with the timber-resource focus of the forestry legislation and subsequent planning for forest use. The scale of forest ownership – in part a function of the restitution legislation – is also addressed in relation to the practicalities of resource management. Generally, the paper demonstrates a mismatch between the postsocialist forestry legislation and local practice and conditions with regard to forests and the natural resources therein. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mechanisms controlling summertime oxygen depletion in western Long Island Sound

Physical profile data (salinity, temperature, oxygen, and downwelling irradiance) and in situ incubations of light and dark bottles were used to characterize vertical structure and elucidate mechanisms controlling summertime hypoxia in western Long Island Sound. The period of oxygen depletion corresponded with the period of thermally-controlled stratification. Bulk density differences between surface and bottom waters were only 1.2 to 2.7 sigma-t units; but they were apparently sufficient to resist destratification by winds and tides. Thus oxygen depletion was a cumulative process through the summer. During the stratification period, net oxygen production (measured using light BOD bottles) was confined to a narrow surface zone of 1.8–4.5 m. Below this zone was an intermediate zone of high net oxygen uptake, beneath which was a subpycnoclinic zone where oxygen uptake was very low. Rates of total oxygen uptake (dark bottles) were greatest in the surface layer and diminished with depth. There was close coupling between physical conditions and metabolic structure. Vertical patterns of oxygen production and removal were strongest in calm weather. The location of the intermediate zone corresponded with that of the oxycline. The thickness of the zone and the steepness of the oxycline were determined by the depth and intensity of both physical stratification and biological production and respiration. The biological structure was weakened by physical mixing in the upper water column, and the intermediate zone disappeared with fall destratification. We hypothesize that biological uptake within the water column influences oxygen depletion through two mechanisms. (1) In bottom waters, uptake rates per unit volume are low, but bulk uptake is a significant factor in oxygen depletion because of the large volume of water involved. (2) The intermediate zone, where respiratory uptake is also significant, is strategically located between the surface zone of oxygen renewal and the bottom zone of depletion, where it constitutes an active filter which reinforces the pycnocline as a barrier to vertical oxygen dispersion. The magnitude of direct oxygen removal in the water column relative to removal by sediment oxygen demand and the potential effects of this biological filtering mechanism are important considerations for understanding eutrophication dynamics and managing Long Island Sound. Dynamic models which (1) underestimate the role of water column uptake and (2) incorporate only the two-zone characteristics of physical stratification will tend to (a) overestimate the contribution of sediments to summertime oxygen deficits and (b) overestimate rates of vertical dispersion and reventilation of bottom waters.     

Conflict,Space, and Resource Management at Grand Canyon*

Geographical spaces and boundaries are neither simple nor naively given. An examination of selected disputes over territory in the greater Grand Canyon area reveals the importance of considering the implications of absolute, relative, and representational spaces for how contests are framed and negotiated. Efforts to move toward a more ecologically based regime of natural resource management at Grand Canyon require a better understanding of how the existing spaces came to have their present location, size, configuration, definition, and jurisdictional structure.     

Recolonization of estuarine sediments by macroinvertebrates: Does microcosm size matter?

Microcosms containing defaunated, fine estuarine sediments were field deployed to assess the effects of microcosm size on the rate of benthic macroinvertebrate recolonization and resulting community structure. Four sizes of microcosms (square acrylic plastic boxes: 7 cm side^?1, 12 cm side^?1, 20 cm side^?1, and 32 cm side^?1, all 6-cm deep) were deployed in upper Perdido Bay, Florida, and colonized for 6 wk. Absolute mean total number of organisms (TNO) differed (α=0.05) among all sizes, while normalized mean TNO (adjusted to 12 cm side^?1 area) did not. Mean total number of taxa (TNT) was different among sizes: 7 cm side^?1, 12 cm side^?1, and 20 cm side^?1, but not between sizes 20 cm side^?1 and 32 cm side^?1. Seven dominant taxa occurred in all size microcosms. Scaling of physical design features (size of microcosm) affected numbers of taxa in recolonization of fine-grained sediments in our study area, but effects on abundance and dominance were minimal.