Destocking as a drought-mitigation strategy: clarifying rationales and answering critiques

The idea of externally assisted emergency destocking of pastoralists has gained currency in recent years: increasing the incentives for pastoralists to sell animals, or removing the constraints to selling animals in the early stages of drought. We identify two separate rationales put forward by proponents of destocking: environmental benefits and purchasing power/welfare benefits. We consider whether specific recent critiques of 'new range ecology' and specifically of 'tracking policies' do in fact provide arguments against emergency destocking in pastoralist areas. We illustrate some of these themes with a case study of a successful destocking exercise in northern Kenya where a very specific form of support was requested and received by pastoralists themselves. The sorts of destocking that work are likely to have significant effects on pastoralist purchasing power at key points of the drought cycle, but minimal effects on the environment. Clarifying these points will make it easier to promote destocking as a drought-mitigation policy.     

Natural uranium and thorium distributions in podzolized soils and native blueberry

Plant uptake of radionuclides is one of many vectors for introduction of contaminants into the human food chain. Thus, it is critical to understand soil-plant relationships that control nuclide bioavailability. Our objectives in this study were to (i) determine the extent of U and Th uptake and cycling by blueberry (Vaccinium pallidum Aiton) in native habitat and (ii) identify the soil properties and processes that contribute most to U and Th bioavailability in this system. We collected composite samples of plant leaves and stems, and samples from surface (AE) horizons and from the upper part of the Bs horizon at two sites. Concentration ratios (CRs) for U and Th were calculated for all plant tissues, using both the AE and Bs horizons as the base. Soil concentrations of U ranged from 16 to 25 microg g(-1), with a mean of 21.1 microg g(-1). Soil concentrations of Th ranged from 14 to 97 microg g(-1), with a mean of 41.8 microg g(-1). Mean U concentrations were 8.65 x 10(-3) microg g(-1) in leaf tissue, and 7.95 x 10(-3) microg g(-1) in stem tissue. Mean Th concentrations were 1.59 x 10(-1) microg g(-1) in leaf tissue, and 9.10 x 10(-2) microg g(-1) in stem tissue. Blueberry plants are cycling both U and Th in this system, with Th cycling occurring to a greater extent than U. In addition, Th was translocated preferentially to plant leaves while U concentrations showed little preferential translocation. Uranium uptake, however, seemed more sensitive than Th uptake to soil properties.     

Calibrating a Basin‐Scale Groundwater Model to Remotely Sensed Estimates of Groundwater Evapotranspiration

Remotely sensed vegetation indices correspond to canopy vigor and cover and have been successfully used to estimate groundwater evapotranspiration (ET_g) over large spatial and temporal scales. However, these data do not provide information on depth to groundwater (dtgw) necessary for groundwater models (GWM) to calculate ET_g. An iterative approach is provided that calibrates GWM to ET_g derived from Landsat estimates of the Enhanced Vegetation Index (EVI). The approach is applied to different vegetation groups in Mason Valley, Nevada over an 11‐year time span. An uncertainty analysis is done to estimate the resulting mean and 90% confidence intervals in ET_g to dtgw relationships to quantify errors associated with plant physiologic complexity, species variability, and parameter smoothing to the 100 m GWM‐grid, temporal variability in soil moisture and nonuniqueness in the solution. Additionally, a first‐order second moment analysis shows ET_g to dtgw relationships are almost exclusively sensitive to estimated land surface, or maximum, ET_g despite relatively large uncertainty in extinction depths and hydraulic conductivity. The EVI method of estimating ET_g appears to bias ET_g during years with exceptionally wet spring/summer conditions. Excluding these years improves model performance significantly but highlights the need to develop a methodology that accounts not only on quantity but timing of annual precipitation on phreatophyte greenness.     

Polynuclear Aromatic Hydrocarbons Associated with Particulates in Pittsburgh Air

Pittsburgh air was sampled continuously at one site for 886 hrs./sample at 45 cfm with a high volume sampler equipped with a horizontal elutriator as a first stage of separation, and an MSA 1106B glass fiber filter as a final particulate collection stage. The horizontal elutriator was designed to simulate the particulate deposition characteristics of the human respiratory tract. Samples were collected during the period June 1964 to February 1965. Respirable and non-respirable particulate samples were analyzed for polynuclear aromatic hydrocarbon content by a new technique which utilized dual column, flame ionization gas chromatography. It was possible to quantitatively analyze a concentrated benzene extract of the particulate sample for the following individual components: 1, 2 benzanthracene; chrysene; pyrene; 3,4 benzofloranthene; 1, 12 benzoperylene. It was not possible to distinguish between 3,4 benzopyrene, 1,2 benzopyrene and perylene; only the total quantity of these compounds present was detected. This analytical technique is comparable in sensitivity to formerly reported, more time-consuming methods and is very rapid, requiring less than one hour to perform after benzene extraction. Amounts of the above compounds associated with the two particulate fractions collected are reported and discussed.     

Song ranging by the dusky antbird,Cercomacra tyrannina: ranging without song learning

In a population of dusky antbirds (Cercomacra tyrannina), less aggressive responses to distance-degraded playbacks than to undegraded playbacks of pair duets show that this tropical suboscine passerine uses sound degradation to range distance from singing conspecifics. This is the first example of song-ranging in a species that does not learn songs, supporting the hypothesis that ranging preceded the song learning that occurs in more recently evolved passerine birds (oscines). Both sexes sing and are able to use song degradation to range distance from singers when their sex-specific song is played back. Received: 27 May 1994/Accepted after revision: 24 March 1996     

New development in the MOCNESS,an apparatus for sampling zooplankton and micronekton

Four variants of the Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) have been constructed to sample a broad size spectrum of oceanic animals from microzooplankton to micronekton. The systems differ in mouth opening dimensions (ranging from 1/4 to 20 m²), the number of nets carried (from 5 to 20), and the mesh size of the netting (from 64 m to 3.0 mm). A new electronics package enables an operator to send commands down a single conductor, armored cable to open/close the nets and provides 12-bit resolution for the environmental (temperature, depth, conductivity) and net operation data (flow, net-frame angle, net-bar release), which are transmitted up the cable to the deck unit at 2-s intervals. A microcomputer system, interfaced to the deck unit, calculates salinity, volume filtered by a net, net trajectory velocity, and vertical velocity. The data are printed out and stored on disc, and profiles of temperature and salinity versus depth are plotted during the course of the tow. Analysis of the relationship between the geometry of the MOCNESS under tow and the past and present methods used to estimate the water filtered by a net revealed that significant bias is introduced when the ascent or descent angle of a net is disregarded. The bias is a function of the ratio of vertical velocity to net trajectory velocity and results in an underestimate of volume filtered while shooting a net and an overestimate while hauling.     

Differences in feeding ecology among three co-occurring species of wrasse (Teleostei: Labridae) on rocky reefs of temperate Australia

The foraging behaviours and dietary compositions of three co-occurring labrids (Ophthalmolepis lineolatus, Notolabrus gymnogenis and Pictilabrus laticlavius), which are conspicuous on rocky reefs in temperate south-eastern Australia, were investigated between 2003 and 2005. SCUBA observations at two locations showed that the feeding intensity, and hence the associated effects of these fishes on rocky reef invertebrate prey, was temporally consistent. Relative differences in the contributions of ingested prey and use of different feeding microhabitats demonstrated that the feeding ecology differed significantly among the three species. Thus, O. lineolatus fed on proportionately higher volumes of polychaetes, polyplacophorans, marginellid gastropods (especially Austroginella sp.), bivalves and echinoids, which were sighted opportunistically in a wide selection of microhabitats, but particularly in sand/rubble. Ambush hunting was used regularly by smaller N. gymnogenis and all sizes of P. laticlavius to forage on amphipods, small decapods and small gastropods at algal bases or fronds and Diopatra dentata tubes. Amphipods were similarly important in the diet of smaller O. lineolatus. Larger N. gymnogenis foraged opportunistically over an increased reef area and made greater use of microhabitats that offered minimal prey refuge (e.g. sand/rubble, bare rock/steel) from which common prey, in particular decapods, were obtained. The significant intra- and inter-specific differences in dietary compositions, allied with differences in the use of feeding microhabitats, would facilitate co-occurrence of these three conspicuous species and contribute to maintaining high richness of labrid species in reef systems. Echinoids were regularly consumed by each species but they made a moderate contribution to the diet of only O. lineolatus, which suggests that only one of the three labrids is likely to play a significant role in regulation of echinoid densities in these rocky reef habitats. However, the broad diets and diverse forging strategies employed by these labrid species imply that they have a system-wide influence on invertebrate prey on rocky reefs.     

Community structure,density and standing crop of fishes in a subtropical Australian mangrove area

The fishes occurring in a subtropical mangrove (Avicennia marina) area in Moreton Bay, Australia, were studied for one year (November 1987 to November 1988, inclusive). Fishes within the mangroves were sampled using a block net, whilst those in adjacent waters were sampled using seine and gill nets. Forty six percent of the species, 75% of the number of fishes and 94% of the biomass taken during the study (all methods combined) were of direct importance to regional fisheries. The fish community utilising the habitat within the mangrove forest differed from that occurring in adjacent waters in terms of density, standing crop, species composition and diversity-index values. Standing-crop estimates for the fishes occurring within the mangroves (study period mean ± SD = 25.3 ± 20.4 g m^–2) were amongst the highest recorded values for estuarine areas whilst those for adjacent waters (2.9±2.3 g m^–2) were comparable to those of other estuarine studies.