Survey of the occurrence of residues of methyl tertiary butyl ether (MTBE) in Dutch drinking water sources and drinking water

An indicative survey has been carried out in The Netherlands investigating the presence of methyl tertiary butyl ether (MTBE) in drinking water and the corresponding sources. In total, 71 different sites used for the preparation of drinking water in The Netherlands were sampled in two successive seasons in 2001 involving the analysis of 156 samples. (ground water (n = 88), surface water (n = 17), bank filtrate water (n = 6) and drinking water (n = 45)). To combine high sample throughput with high selectivity and sensitivity, off-line purge and trap for sampling and gas chromatography mass spectrometry equipped with an automated thermal desorption sampler (TDS-GC-MS) was selected as the preferred analytical methodology. The developed procedure enabled the analysis of at least 40 samples per day and provided a limit of quantification of 2 ng l(-1). In the first period 63 samples of raw water were analyzed. Concentrations ranged between < 10 ng l(-1) and 420 ng l(-1) with a median concentration below 10 ng l(-1). The second period was focused at the re-sampling of positive locations (MTBE > 10 ng l(-1)) and a few additional drinking water utilities of which both the raw and drinking water of the utilities were analyzed. The median concentration of MTBE in the selected set of drinking water samples was 20 ng l(-1) (n = 45). At one location MTBE was found at a level of 2900 ng l(-1) caused by point source contamination of the ground water (11 900 ng l(-1)). Special attention has been paid to the quality of the results by analyzing all samples in duplicate and the analysis of control samples during each series of analyses.     

Desert pastoralists’ negative and positive effects on rare wildlife in the Gobi

In arid regions of the developing world, pastoralists and livestock commonly inhabit protected areas, resulting in human–wildlife conflict. Conflict is inextricably linked to the ecological processes shaping relationships between pastoralists and native herbivores and carnivores. To elucidate relationships underpinning human–wildlife conflict, we synthesized 15 years of ecological and ethnographic data from Ikh Nart Nature Reserve in Mongolia's Gobi steppe. The density of argali (Ovis ammon), the world's largest wild sheep, at Ikh Nart was among the highest in Mongolia, yet livestock were >90% of ungulate biomass and dogs >90% of large‐carnivore biomass. For argali, pastoral activities decreased food availability, increased mortality from dog predation, and potentially increased disease risk. Isotope analyses indicated that livestock accounted for >50% of the diet of the majority of gray wolves (Canis lupus) and up to 90% of diet in 25% of sampled wolves (n = 8). Livestock composed at least 96% of ungulate prey in the single wolf pack for which we collected species‐specific prey data. Interviews with pastoralists indicated that wolves annually killed 1–4% of Ikh Nart's livestock, and pastoralists killed wolves in retribution. Pastoralists reduced wolf survival by killing them, but their livestock were an abundant food source for wolves. Consequently, wolf density appeared to be largely decoupled from argali density, and pastoralists had indirect effects on argali that could be negative if pastoralists increased wolf density (apparent competition) or positive if pastoralists decreased wolf predation (apparent facilitation). Ikh Nart's argali population was stable despite these threats, but livestock are increasingly dominant numerically and functionally relative to argali. To support both native wildlife and pastoral livelihoods, we suggest training dogs to not kill argali, community insurance against livestock losses to wolves, reintroducing key native prey species to hotspots of human–wolf conflict, and developing incentives for pastoralists to reduce livestock density.     

GROUND-WATER RECHARGE THROUGH ACTWE SAND DUNES IN NORTHWESTERN NEVADA1

ABSTRACT: Most water-resouree investigations in semiarid basins of the Great Basin in western North America conclude that ground-water recharge from direct precipitation on the valley floor is negligible. However, many of these basins contain large areas covered by unvegetated, active sand dunes that may act as conduits for ground-water recharge. The potential for this previously undocumented recharge was investigated in an area covered by sand dunes in Desert Valley, northwestern Nevada, using a deep percolation model. The model uses daily measurements of precipitation and temperature th determine energy and moisture balances, from which estimates of long-term mean annual recharge are made. For the study area, the model calculated a mean annual recharge rate of as much as 1.3 inches per year, or 17 percent of the long-term mean precipitation. Model simulations also indicate that recharge would be virtually zero if the study area were covered by vegetation rather than dunes.