SOIL: AN OVERLOOKED, UNDERVALUED AND VITAL PART OF THE HUMAN ENVIRONMENT

Soils are taken for granted by the majority of the human population, but despite the image of being just dirt, soils are an extremely important component of the environment. Soils can be observed to have a complex structure, with unique biological, chemical and physical characteristics. They support plants, the primary producers, and supply them with moisture and nutrients, so providing all other terrestrial ecosystems with the basis of the food chain. With the exception of small contributions from aquatic sources, virtually all human food is produced either directly from crops grown in soils, or from animals which graze upon herbage itself rooted in the soil. Soils are under considerable threat from over-exploitation, pollution and misuse. Many decisions about land use are made without consideration of the underlying soils and for any serious proposals for sustainable use of the land, soil properties and functions should be recognized. Soils participate in the hydrological cycle, as well as the cycling of carbon, nitrogen, sulphur and phosphorus. They intercept, absorb and inactivate pollutants, but also produce greenhouse gases. Soils have long been recognized as a major natural body, worthy of investigation in their own right, and are now also being seen as a major participant in the global cycles of the environment.     

Euro Chlor Risk Assessment for the Marine Environment Osparcom Region: North Sea - Trichloroethylene

This risk assessment on trichloroethylene (TRI) was carried out specifically for the marine environment, according to the methodology laid down in the EU risk assessment Regulation (1488/94) and the Guidance Document of the EU New and Existing Substances Regulation (TGD, 1997). The study consists of the collection and evaluation of data on effects and environmental concentrations from analytical monitoring programs in large rivers and estuaries in the North Sea area. The risk is indicated by the ratio of the "predicted environmental concentrations" (PEC) and the "predicted no effect concentrations" (PNEC) for the marine aquatic environment. In total, 19 studies for fish, 30 studies for invertebrates and 14 studies for algae have been evaluated. Both acute and chronic toxicity studies have been taken into account and the appropriate assessment factors have been used to define a PNEC value of 150 µg/l. Most of the available monitoring data apply to rivers and estuaries and were used to calculate PECs. The most recent data (1991-1995) support a typical PEC of 0.1 µg TRI/l water and a worst case PEC of 3.5 µg TRI/l water. The calculated PEC/PNEC ratios give a safety margin of 40 to 1,500 between the predicted no effect concentration and the exposure concentration. Additional evaluation of environmental fate and bioaccumulation characteristics showed that no concern for food chain accumulation is expected.     

Spatial variation in dimethylsulfoniopropionate (DMSP) production in <Emphasis Type="Italic">Ulva lactuca</Emphasis> (Chlorophyta) from the Northeast Pacific

Although dimethylsulfoniopropionate (DMSP) has a variety of functions in marine macroalgae including that of a cryoprotectant, an osmolyte, a way to remove excess sulfur and energy, an antioxidant, and an allelopathic precursor, the latter two functions are believed to be the most important in Ulva lactuca L. (=U. fenestrata) in intertidal populations on the coast of Washington state, USA. The present study found significant variation in DMSP concentrations among U. lactuca collected in May 2005 from six sites ranging from 47°54.45′N (Possession Point, Whidbey Island, WA, USA) to 48°30.55′N (Shannon Point Beach, Anacortes, WA, USA), and also among individuals within sites, and among tissues (basal tissues near the holdfast, middle of the blades, and tips). Concentrations ranged from 37 to 224 μmol g⁻¹ fresh mass (FM). In several 10-day experiments between July 2001 and August 2004 with U. lactuca collected from several places on the coast of Washington, the effects of nutrient level (DIN), light intensity and wavelength, and grazing by the herbivorous gastropod Lacuna vincta, were examined. None of these manipulations resulted in DMSP concentrations that differed significantly from controls, and variance in DMSP concentrations within each experiment was very low. Although DMSP concentrations in U. lactuca may be affected by factors not tested in these experiments, it is also possible that the observed spatial differences reflect constitutive genotypic or phenotypic differences among geographically separated U. lactuca populations or among cryptic Ulva species. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

On marketable air-pollution permits: The case for a system of pollution offsets

After examining the properties of several alternative forms of marketable permit systems for the control of air pollution, this paper proposes a system of pollution offsets as the most promising approach. Under the pollution-offset scheme, sources of emissions are free to trade emissions permits subject to the constraint of no violations of the predetermined air-quality standard at any receptor point. The paper shows that the pollution-offset system has the capacity to achieve the predetermined standards of air quality at the minimum aggregate abatement cost, while making comparatively modest demands both on the sources and on the administering agency.     

Dynamic simulation of water depletion in the root zone

The joint effect of the distribution of the soil water potential and of the root mass in the crop root zone upon the water uptake by the crop is represented by a simple equation. This expression is used to join a layered crop canopy model for finding the evapotranspiration, as controlled by stomatal action and the weather, with a hydraulic flow model for the root zone and the underlying soil. The complete model is used for the calculation of the water extraction pattern and the changes, with time, of other plant and soil processes. A simulation of a 20-day drying period is performed, using S/360 CSMP, for a constant diurnal weather pattern, and for a fully developed sorghum crop. The results show that, after a few days of essentially constant water use by the crop, a monotonic decline sets in, that is principally attributable to the decrease in transpiration. For the entire drying period a substantial amount of water - about 30% of the total used - is contributed by upward flow into the root zone from the soil below. The results demonstrate the difficulty of quantitative definition of concepts such as “field capacity”, “wilting percentage”, and “available” or “extractable” water.     

Temporary natural resource cartels

We analyze the behavior of a nonrenewable resource cartel that anticipates being forced, at some date in the future, to break up into an oligopolistic market in which its members will then have to compete as rivals. Under reasonable assumptions about the value function of the individual firms in the oligopolistic equilibrium that follows the breakup, we show that the cartel will then produce more over the same interval of time than it would if there were no threat of dissolution, and that its rate of extraction is a decreasing function of the cartel's life; that there are circumstances under which the cartel will attach a negative marginal value to the resource stocks, in which case the rate of depletion will be increasing over time during the cartel phase; that, for a given date of dissolution, the equilibrium stocks allocated to the post-cartel phase will increase as a function of the total initial stocks, whereas those allocated to the cartel phase will increase at first, but begin decreasing beyond some level of the total initial stocks.     

Ungulate Reintroductions: Experiences with the Takhi or Przewalski Horse (Equus ferus przewalskii) in Mongolia

Experiences with the reintroduction of the takhi, or Przewalski horse ( Equus ferus przewalskii , in Mongolia can serve as valuable lessons for reintroduction of ungulates in general. We discuss the present taxonomic, historical, and biological evidence and conclude that the takhi should be viewed as a typical steppe herbivore. Its last refuge, the Dzungarian Gobi, should therefore be seen as a marginal habitat because it consists mainly of desert and semidesert. Since 1992 two reintroduction projects have been in the acclimatization phase in Mongolia. Despite promising developments, problems with cooperation, management, habitat choice, insufficient knowledge of the ethology of the species, and current land use within the different project areas could jeopardize the successful reintroduction of takhi. We review the conditions required for a potentially successful ungulate reintroduction. The planning of a reintroduction within the framework of safeguarding an entire ecosystem with an integrated management plan appears essential. Each potential reintroduction site should be assessed thoroughly for its suitability, including size, habitat types, current land use, socioeconomics, legislation, and potential problems. Each site should be provided with one or more acclimatization facilities to harbor genetically and physically healthy, socially adapted animals in biologically sound groups. An organization structure should be established for each reintroduction site. Its objective should be to develop an effective management plan and to carefully monitor the population and its surrounding ecosystem. Special attention should be given to local socioeconomic situations, community participation, and training of staff for management, research, and ranger and warden activities.     

Pattern of planktonic bioluminescence in the northern Sargasso Sea: Seasonal and vertical distribution

The vertical structure of bioluminescence potential (BPOT) and flash density (FD) were measured on five cruises to the northern Sargasso Sea in 1987 and 1988. Depth-integrated (0 to 150 m) BPOT did not vary seasonally, remaining within the range 9 to 15 × 10¹⁵ photons m^–2 in all months sampled. Conversely, depth-integrated FD was significantly higher (> 2 × 10⁵ flashes m^–2) during winter (November and March) than during summer (< 9 × 10⁴ flashes m^–2 in May and August). The vertical patterns of BPOT and FD were well correlated within a single profile, more highly so in summer than in winter. Despite intracruise variability in the vertical pattern of BPOT and FD, there were clear summer-winter differences in the vertical distribution of BPOT and FD. During winter, BPOT and FD were maximal and relatively uniform throughout the surface mixed layer; for example in November they declined sharply within the thermocline at 130 to 150 m. During summer, BPOT and FD were greatest (12 to 25 × 10¹³ photons m^–3 and 600 to 1 200 flashes m^–3, respectively) at subsurface depths. Commonly in summer, the upper depth limit of high BPOT and FD occurred at the base of the surface mixed layer (10 to 40 m) and the lower depth limit was located at the base of the subsurface fluorescence maximum (usually at 100 to 120 m).     

Seasonal exposures to triazine and other pesticides in surface waters in the western Highveld corn-production region in South Africa

The objective of this study was to characterize concentrations of atrazine, terbuthylazine, and other pesticides in amphibian habitats in surface waters of a corn-production area of the western Highveld region (North-West Province) of South Africa. The study was conducted from November 2001 to June 2002, coinciding with the corn-production season. Pesticide residues were measured at regular intervals in surface water from eight ponds, three in a non-corn-growing area (NCGA) and five within the corn-growing area (CGA). Measured atrazine concentrations differed significantly among sites and between samples. In the five CGA sites, the maximum atrazine concentrations measured during the study ranged from 1.2 to 9.3 microg/L. Although no atrazine was recorded as being applied in the catchment of the three NCGA sites, maximum concentrations from 0.39 to 0.84 microg/L were measured during the study, possibly as a result of atmospheric transport. Maximum measured concentrations of terbuthylazine ranged from 1.22 to 2.1 microg/L in the NCGA sites and from 1.04 to 4.1 microg/L in the CGA sites. The source of terbuthylazine in the NCGA sites may have been in use other than in corn. The triazine degradation products, deisopropylatrazine (DIA) and deethylatrazine (DEA) and diaminochlorotriazine (DACT) were also found in water from both the CGA and NCGA sites. Concentrations of DIA were > or = 1 microg/L throughout the season, while DEA concentrations were mostly <0.5 microg/L before planting but increased after planting and application of herbicides to concentrations >2 microg/L in some locations. Concentrations of DACT were highly variable (LOD to 8 microg/L) both before and after planting and application, suggesting that they resulted from historical use of triazines in the area. Other herbicides such as simazine and acetochlor were only detected infrequently and pesticides such as S-metolachlor, cypermethrin, monocrotophos, and terbuphos, known to be used in the CGA, were not detected in any of the samples. Because of dilution by higher than normal rainfall in the study period, these concentrations may not be predictive of those in years of normal rainfall.