Identification of critical areas on forest lands for control of nonpoint sources of pollution

Most nonpoint source pollution problems on forest lands can be controlled by careful planning and management of specific critical areas. Critical areas include sites with high mass and surface erosion hazards, overland flow areas, and the riparian zone. Some guides for identifying critical areas are presented along with examples of land-use constraints that might be applied.     

BEDROCK CONTROLS ON STREAM CHANNEL ENLARGEMENT WITH URBANIZATION,NORTH CENTRAL TEXAS1

Loss due to channel erosion in the Dallas, Texas, area is estimated to approach one-half million dollars in the last several years. Hydrogeomorphic analysis of natural and urban chalk and shale watersheds was performed in the central Texas area on watersheds ranging in size from 0.5 to 10 square miles in an effort to more adequately predict channel enlargement due to urbanization. Chalk watersheds were found to have greater drainage density, greater channel slope, lower sinuosity, and greater discharge per unit area than similar sized shale watersheds under natural conditions. With subsequent urbanization of the watersheds, chalk channel enlargement was from 12 to 67 percent greater than shale channel enlargement for similar sized watersheds. Greater enlargement in chalk channels is attributed to greater channel velocities and unit tractive force. Vegetation seems to play a significant role in influencing channel adjustments to the new flow regimes brought on by urbanization. Channel response to urbanization is documented and specific nonstructural guidelines are proposed which could reduce structural loss along urban stream channels.     

Disembodied and Disembedded? The Social and Economic Implications of Atmospheric Change and Biodiversity

The social and economic implications of atmospheric change on biodiversity need to be seen in a global context of major shifts in the conceptualization and management of our relationship with nature. Traditionally, we have conceptualized the atmosphere and the other creatures of the biosphere as separate from the human, but their quasi-autonomy is now becoming subject to more and more human management. This raises not only economic issues, but social, political, and ethical concerns that will have substantial influence on public policy. Among these are the commodification of genetic material; the privatization of traditional knowledge; and the management of information. In this broader context, the paper examines an array of current and proposed strategies of response to changes in biodiversity as a result of climatic and other stresses.     

Development of an integrative passive sampler for the monitoring of organic water pollutants

The development of convenient and competitive devices and methods for monitoring of organic pollutants in the aquatic environment is of increasing interest. An integrative passive sampling system has been developed which consists of a solid poly(dimethylsiloxane) (PDMS) material (tube or rod), acting as hydrophobic organic receiving phase, enclosed in a water-filled or an air-filled low-density polyethylene (LDPE) membrane tubing. These samplers enable the direct analysis of the pollutants accumulated during exposure in the receiving phase by thermodesorption-GC/MS, avoiding expensive sample preparation and cleanups. The capabilities of these sampling devices were studied for the sampling of 20 persistent organic pollutants (chlorobenzenes, hexachlorocyclohexanes, p,p'-DDE, PAHs, and PCBs) in laboratory exposure experiments. For the three sampler designs investigated the uptake of all target analytes was integrative over exposure periods up to 9 days (except PCB 101). The determined sampling rates range from 4 to 1340 microl h(-1) for the water-filled samplers and from 20 to 6360 microl h(-1) for the air-filled ones, respectively. The sampling rate of the analytes is dependent on their molecular weight, partition between water and sampler media (PDMS, polyethylene, water, air) and also of the sampler design. The passive samplers enable the estimation of time-weighted average (TWA) concentration of water pollutants in the lower ng l(-1) to pg l(-1) range.     

Combined use of rapid bioassessment protocols and sediment quality triad to assess stream quality

Physical, chemical and biological conditions at five stations on a small southeastern stream were evaluated using the Rapid Bioassessment Protocols (RBP) and the Sediment Quality Triad (SQT) to assess potential biological impacts of a municipal wastewater treatment facility (WWTF) on downstream resources. Physical habitat, benthic macroinvertebrates and fish assemblages were impaired at Stations 1 and 2 (upstream of the WWTF), suggesting that the degraded physical habitat was adversely impacting the fish and benthic populations. The SQT also demonstrated that Stations 1 and 2 were degraded, but the factors responsible for the impaired conditions were attributed to the elevated concentrations of polycylclic aromatic hydrocarbons (PAHs) and metals (Mn, Pb) in the sediments. The source of contaminants to the upper reaches of the stream appears to be storm-water runoff from the city center. Increased discharge and stabilized base flow contributed by the WWTF appeared to benefit the physically-altered stream system. Although the two assessment procedures demonstrated biological impairment at the upstream stations, the environmental factors identified as being responsible for the impairment were different: the RBP provided insight into contributions associated with the physical habitat and the SQT contributed information on contaminants and sediment quality. Both procedures are important in the identification of physical and chemical factors responsible for environmental impairment and together they provide information critical to the development of appropriate management options for mitigation.     

Adsorption of antimony(V) by floodplain soils, amorphous iron(III) hydroxide and humic acid

Antimony (Sb) emissions to the environment are increasing, and there is a dearth of knowledge regarding Sb fate and behaviour in natural systems. In particular, there is a lack of understanding of sorption of the oxidised Sb(V) species onto soils and soil phases. In this study sorption of Sb(V) by two organic rich soils with high levels of oxalate extractable Fe was examined over the pH range of 2.5-7. Furthermore, the sorption behaviour of Sb(V) was examined in two phases mimicking those dominant in the experimental soils, namely a solid humic acid and an amorphous Fe(OH)3, across the same pH range. Sorption of Sb by the soils and the humic acid fitted a Freundlich type isotherm, with the equation parameters reflecting changes in bonding affinity corresponding to pH changes. The soils sorbed >75% of the added Sb in all trials, and 80-100% at pH values less than approximately 6.5. The Fe(OH)3 retained >95% of the added Sb in all experiments. The humic acid sorbed up to 60% of the added Sb at acidic pH values, but sorption decreased to zero at higher pH values. Further adsorption studies are recommended, such as examining the effects of ion competition and changes in ionic strength.     

Monitoring ammonia in urban, inner alpine and pre-alpine ambient air

Passive samplers were used to monitor ammonia concentrations at rural inner alpine and pre-alpine, as well as urban, sites in Austria and Bavaria. Elevated concentrations were measured both at farms (up to 36 microg NH3 m(-3)) and at urban locations (up to 28 microg NH3 m(-3)). At urban locations a linear relationship between the traffic density and the NH3 concentration was found, but there was no marked seasonal trend. The highest ammonia concentrations were measured in a traffic tunnel (up to 78 microg NH3 m(-3)). The presence of livestock breeding or small scale alpine pastures resulted in elevated concentrations at the rural sites (8.1-12 and 2.5-4.6 microg NH3 m(-3), respectively), compared to the surrounding areas (3.1 and 0.9 microg NH3 m(-3)). Agriculture related sources are usually limited either spatially or seasonally. As the emissions were moderate in our case, a rapid removal and dilution of ammonia was possible and therefore the NH3 burden was only local. Sources related to traffic are more evenly distributed both geographically and seasonally. The WHO guideline, annual average concentration of 8 microg m(-3) for the protection of vegetation, was only exceeded at farms, at the urban station with the heaviest traffic and in the Tauerntunnel.     

Multi-element geochemical analysis of snow samples: Use of discriminant analysis in interpreting the results

This paper records the concentrations of major and trace elements determined from snow samples collected during a comprehensive survey undertaken in the Scottish Highlands during the winter and spring period of 1987. The configuration of calculated back-trajectories allowed the samples to be categorized into one of five geographical sectors. Discriminant analysis was used to check the validity of these calculations, to isolate potentially deviant samples, and to predict the possible source of one sample whose back-trajectory could not be computed with confidence. Limitations of the statistical method are discussed, but we conclude that the technique justifies more use by environmental scientists involved in the evaluation of data.