Temporal salinity variation in salt evaporation basins in south-eastern Australia

Salt evaporation basins in south-eastern Australia, in contrast with natural saline lakes in this region, were not highly saline and exhibited little seasonal pattern in water depth and salinity over a 2-year sampling period. Lack of seasonality arose from either constant inflow (from continuous groundwater pumping) or erratic inflow (from unpredictable irrigation demands). Differences in zooplankton species composition between the salt evaporation basins and natural saline lakes might reflect the differences in temporal salinity patterns. Some typical saline lake zooplankton were not found in the evaporation basins. Salt evaporation basins therefore may represent additions to the inland water habitats of semi-arid Australia.     

Pre-eruptive melt composition and constraints on degassing of a water-rich pantellerite magma,Fantale volcano,Ethiopia

To determine the pre-eruptive composition of peralkaline magma at Frantale volcano, Ethiopia, we have studied glass inclusions in phenocrysts from a lateceupting, glassy pantelleritic lava flow. Matrix glass and crystal-free glass inclusions in quartz were analyzed for all major and most minor elements by electron microprobe and for H₂O and 15 lithophile trace elements by ion microprobe (SIMS). Compositions of inclusions may have been slightly modified by post-trapping quartz crystallization, the average concentrations of all constituents but silica may be artificially high by 10% relative. Glass inclusions contain extreme enrichments in H₂O (mean of 4.6 to 4.9 wt%) and several lithophile trace elements, which suggest that the lava erupted from a highly evolved, water-rich fraction of magma. The pre-eruptive concentration of water was much higher than that generally considered to occur in pantellerite magmas. Trends observed for lithophile elements in whole-rock samples from pre-,syn-and post-caldera eruptive units are mimicked in glass inclusions from the studied pantellerite lava; concentrations of Rb, Y, Zr, Nb, and Ce±Cl increase with progressive differentiation. With the exception of Cl and H₂O contents, the composition of matrix glass is similar to that of glass inclusions suggesting: that few constituents exsolved from magma or cooling glass; eruption and quench of the lava occurred rapidly; and the matrix glass is, largely, compositionally representative of melt. Higher average abundances of Cl and H₂O in glass inclusions suggest that these volatiles exsolved after melt entrapment; degassing could have occurred as either an equilibrium or disequilibrium process.     

Effects of sampling microhabitats with low coverage within the STAR/AQEM macroinvertebrate sampling protocol on stream assessment

In the STAR/AQEM protocol microhabitats covering less than 5% of the sampling area were neglected. Driven by an ongoing discussion on the importance of these underrepresented microhabitats we tested the influence of sampling them. We investigated 48 streams representing 14 different stream types from all over Germany. Macroinvertebrates of underrepresented microhabitats were sampled in addition to the STAR/AQEM protocol. To ensure the method remains feasible in routine monitoring programmes the total sampling and sorting effort of additional sampling was limited to 20 min. Particularly those taxa were picked, which were not recognised during the routine STAR/AQEM sorting.To identify the effect of additional sampling on stream assessment results, we calculated the stream type-specific Multimetric Index (MMI) with the “main” and the “main+additional” data for each sample. The mean and median difference in MMI values between “main” and “main+additional” samples was 0.02 and 0.01, respectively. In seven of 48 samples (14.6%) a different ecological quality class was calculated with the “main+additional” dataset. Regarding common metrics within the MMI as well as intercalibration metrics differences between “main” and “main+additional” samples were analysed. The values differed most in richness metrics (e.g., number of EPTCBO Taxa, number of Trichoptera Taxa). The results of the present study show that additional sampling of underrepresented microhabitats could alter multimetric assessment results.     

Distribution of Palaeozoic reworking in the Western Arunta Region and northwestern Amadeus Basin from 40Ar/39Ar thermochronology: implications for the evolution of intracratonic basins

The Centralian Superbasin in central Australia is one of the most extensive intracratonic basins known from a stable continental setting, but the factors controlling its formation and subsequent structural dismemberment continue to be debated. Argon thermochronology of K-feldspar, sensitive to a broad range of temperatures (∼150 to 350 °C), provides evidence for the former extent and thickness of the superbasin and points toward thickening of the superbasin succession over the now exhumed Arunta Region basement. These data suggest that before Palaeozoic tectonism, there was around 5–6 km of sediment present over what is now the northern margin of the Amadeus Basin, and, if the Centralian superbasin was continuous, between 6 and 8 km over the now exhumed basement. ⁴⁰Ar/³⁹Ar data from neoformed fine-grained muscovite suggests that Palaeozoic deformation and new mineral growth occurred during the earliest compressional phase of the Alice Springs Orogeny (ASO) (440–375 Ma) and was restricted to shear zones. Significantly, several shear zones active during the late Mesoproterozoic Teapot Orogeny were not reactivated at this time, suggesting that the presence of pre-existing structures was not the only controlling factor in localizing Palaeozoic deformation. A range of Palaeozoic ages of 440–300 Ma from samples within and external to shear zones points to thermal disturbance from at least the early Silurian through until the late Carboniferous and suggests final cooling and exhumation of the terrane in this interval. The absence of evidence for active deformation and/or new mineral growth in the late stages of the ASO (350–300 Ma) is consistent with a change in orogenic dynamics from thick-skinned regionally extensive deformation to a more restricted localized high-geothermal gradient event.     

Implementing a Method of Screening One-Well Hydraulic Barrier Design Alternatives

This article provides details of applying the method developed by the authors ( Rubin et al. 2008b ) for screening one-well hydraulic barrier design alternatives. The present article with its supporting information (manual and electronic spreadsheets with a case history example) provides the reader complete details and examples of solving the set of nonlinear equations developed by Rubin et al. (2008b) . It allows proper use of the analytical solutions and also depicting the various charts given by Rubin et al. (2008b) . The final outputs of the calculations are the required position and the discharge of the pumping well. If the contaminant source is nonaqueous phase liquid (NAPL) entrapped within the aquifer, then the method provides an estimate of the aquifer remediation progress (which is a by-product) due to operating the hydraulic barrier.     

Metazooplankton communities in the Ahe atoll lagoon (Tuamotu Archipelago, French Polynesia): Spatiotemporal variations and trophic relationships

Metazooplankton abundance, biomass (<80μm, 200-500μm and >500μm) and community structure in the Ahe atoll were studied together with their relationships with environmental factors (temperature, salinity, wind) and trophic factors (phytoplankton, bacteria, heterotrophic nanoflagellates (HNF) and ciliates) during three periods in 2008-2009. Meroplankton, mainly bivalve and gastropod larvae, was dominant. Holoplankton was dominated by copepods, the main species being Oithona spp., Paracalanus parvus, Clausocalanus spp., Corycaeus spp., Acartia fossae and Undinula vulgaris. The results suggest a clear wind influence on the structure and horizontal distribution of the zooplankton communities. The metazooplankton appeared to be controlled mainly by food resources, suggesting a bottom-up control. The low nanophytoplankton biomass in contrast to the high abundance of picophytoplankton, HNF and nano-particle grazers (mainly Oithona spp., Paracalanus and bivalve larvae) highlighted the importance of the microbial loop in the food web.