Verteilung verkehrsbedingter Edelmetallimmissionen in Böden

Contents and distribution of platinum-group-elements (PGE) in soils caused by automobile emissions were investigated at three transects perpendicular to the road at various depths. Concentrations of platinum, rhodium and palladium were determined by ICP-MS after separation and preconcentration by nickel-sulphide fire-assay. Platinum contents in roadside soils range from 250 μg/kg to the local background values which are below 0.5–0.8 μg/kg. Ratios of platinum and rhodium (about 6∶1) are similar to the ratios in catalytic converters. There is evidence for a significant correlation of PGE input and local parameters such as traffic-conditions, distance from the trafficlane, prevailing wind direction, and barriers such as vegetation or morphology.     

On the gains of committing to inefficiency: Corruption, deforestation and low land productivity in Latin America

We present a new explanation and empirical evidence showing that rural subsidies to large farmers tend to be associated with low land productivity and excessive deforestation. We develop a lobbying model where wealthy farmers trade bribes or political contributions to government politicians in exchange for subsidies; farmers are able to tilt the terms of the bargaining game with policy makers in their favor by pre-committing to an inefficient choice of semi-fixed inputs. Government proneness to accept political contributions or bribes and its willingness to provide subsidies cause farmers to adopt inefficient modes of production as a mechanism to capture such subsidies. Our predictions are consistent with stylized facts on land use in Latin America, and suggest that subsidy schemes have been counterproductive—distorting and constraining development, and triggering excessive depletion of natural resources. We validate some of the predictions of the model through econometric analyses using a new data set for nine countries in Latin America.     

Differential tolerance to metals among populations of the introduced bryozoan Bugula neritina

Resistance to heavy metals is a potentially important trait for introduced marine organisms, facilitating their successful invasion into disturbed natural communities. We conducted laboratory and field experiments to examine differential resistance to copper (Cu) between two source populations of the introduced bryozoan Bugula neritina, originating from a polluted (Port Kembla Harbour, NSW, Australia) and an unpolluted (Botany Bay, NSW, Australia) environment. A laboratory toxicity test was conducted to test the relative resistance of B. neritina recruits from the two sources, by measuring the attachment success, survival and growth of individuals exposed to a range of Cu concentrations (0, 25, 50 and 100 μg l⁻¹ Cu). Upon completion, reciprocal transplantation of the colonies to the original polluted and unpolluted locations was carried out to assess ongoing survival and growth of colonies in the field. B. neritina colonies originating from the polluted Port Kembla Harbour had increased resistance to Cu relative to populations from an unpolluted part of Botany Bay. There appeared to be a cost associated with increased metal tolerance. In the laboratory, Botany Bay recruits displayed significantly higher growth in control treatments and significantly poorer growth at 100 μg l⁻¹ Cu with respect to Port Kembla Harbour individuals, which showed unusually uniform and low growth irrespective of Cu concentration. No difference in attachment success or post-metamorphic survival was observed between populations. Field transplantation showed copper resistance in Port Kembla Harbour colonies constituted an advantage in polluted but not benign environments. The findings of this study provide evidence of the benefits to invasive species of pollution tolerance and suggest that human disturbance can facilitate the establishment and spread of invasive species in marine systems.     

Effects of Water Management on the Wetlands of the Colorado River Delta, Mexico

The lower delta of the Colorado River has been severely affected by the upstream diversion of water for human use. No river water is officially appropriated to support delta wetlands, yet large marsh areas of conservation interest still exist below the agricultural fields in Mexico. These are supported by flood water, agricultural drainage water, municipal sewage effluent, and seawater in the intertidal zone. From 1973 to 1993 the area of freshwater and brackish marsh varied widely, from 5800 to 63,000 ha. A new opportunity exists to restore wetlands in the delta now that the upstream water impoundments on the Colorado River are filled and flood flows are once again being directed to the delta. But flood control structures now channel most of the flood water directly to the sea, and most of the effluent waters are deposited in evaporation basins rather than used to support wetlands. If the Yuma Desalting Plant in the United States becomes operational and if the Rio Hardy wetlands continue to be drained, the area of brackish wetlands could decrease to less than 2000 ha in the near future. Preserving the remaining wetlands will require a binational water management plan. The plan should maximize the benefits to wetlands of flood and irrigation return flows that enter the delta, and it should minimize flood risks.     

Agricultural Land Use and Grassland Habitat in Illinois: Future Shock for Midwestern Birds?

Populations of many common grassland birds in the midwestern United States have been declining in recent decades. These declines have been particularly pronounced in Illinois, where the prairie has been severely fragmented and disturbed by farming. This article describes transitions in agricultural land use in Illinois since the early 1800s, their effects on grassland habitat, and responses by avifauna. Furthermore, factors affecting nesting by birds are considered from a landscape perspective for a study area in central Illinois during the period (1973–1981) when cropping became so intensive that grassland persisted primarily as linear edges. There was a paucity of avifauna nesting on grassy edge habitats on the study area, with a mean of 2.2 nests per ha, representing only eight species. Nest densities and species diversity were highest on study plots where grassland was nearby, where cover types were heterogeneous, and where there were corridors connecting plots to the surrounding landscape. Nest success was variable from year to year, and for Ring-necked Pheasants ( Phasianus colchicus ) the average annual nest success on edge habitats was positively related to the total amount of grassy cover (including hay and small grains) per nesting pleasant. The findings suggest that it is too simplistic to conclude that linear habitats, compared to field settings, are "predator traps." Responses by birds to habitat deteríoration in Illinois may foretell future trends elsewhere in North America where farming practices are becoming more intensive.     

Suburban growth controls and the price of new housing

The effect of Petaluma, California's growth control program on new house prices is examined by a comparative (quasi-experimental) design, using statistical controls. The difference in price increases between Petaluma and two comparison cities is calculated for houses of standard quality and for average actual houses in each city. It was found that prices of standard quality houses increased significantly more in Petaluma than in one of the comparison cities but not the other. A similar pattern was observed for actual houses. Reasons for the observed results and specific causes of the growth control effect are analyzed.     

Shark attraction using a video-acoustic system

An underwater television system located off Bimini, Bahamas, was used to observe and record the attraction of free-ranging sharks to a nearby sound source. Several species of sharks were attracted by irregularly pulsed signals either containing harmonics (e.g., overdriven sine waves) or consisting of octave bands of noise. Irregularly pulsed, pure tones and harmonic sounds above 1000 Hz were apparently not attractive. Attraction was not reinforced, and habituation of the approach response was regularly observed in prolonged test series. As the number of sharks in the test area increased, swimming activity rose dramatically. Circling and crisscrossing of the site became more intense under conditions of low ambient light and turbidity. Additional tests showed that minimum attractive sound levels were remarkably low, and that sharks could locate a sound source within seconds from distances beyond our limit of visibility (about 25 m).