Long-term efficiency of catalytic converters operating in Mexico City

A 1999 ordinance by the Government of Mexico City bans 1993 model-year vehicles from on-road operation if their catalytic converters are not replaced with new ones. To validate the benefits of this action, we examined three issues related to exhaust emissions of vehicles equipped with catalytic converters. After selecting representative fleets of in-use vehicles, a comparison between emissions and catalyst efficiency in cars with two categories of exhaust emission limits was carried out. For that purpose, two fleets were selected, each made up of 10 vehicles run under similar conditions. A third, larger fleet with emissions control systems was used to evaluate and simulate real-world conditions of vehicles in a controlled laboratory. Finally, the aging effect on the catalytic converter was studied on vehicles run for 100,000 km, replacing their old emission control devices for new ones. The 1991-1992 model-year vehicles showed a high percentage of compliance with the corresponding emissions standard (90%) in comparison with 1993 model-year and later vehicles (Tier 0). However, NOx emissions were higher for the newer vehicles. Fifty percent of the 1991-1992 model-year vehicles evaluated under the official inspection/maintenance (I/M) procedure did not meet the regulated emissions standard when the results were compared with those of the U.S. Federal Test Procedure FTP-75. Our results suggest that the replacement of old catalytic converters with new ones will have little effect on decreasing polluting emissions because these vehicles were in very bad mechanical condition. Results of catalytic activity as a function of mileage indicated inefficient catalyst performance for the fleets tested. All pollutant conversions were below 90% efficiency, and they deteriorated by an average of 30% after the vehicles were run for 100,000 km.     

Occurrence of polybrominated diphenylethers, polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls in coastal sediments from Spain

Fifteen sediment samples were analysed in order to determine their content of polybrominated diphenylethers (PBDEs), polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs). Samples were collected from several hot spots on the Spanish coast, such as the harbours of Almeria and Tarragona, and the mouths of the Besos and Llobregat rivers in Barcelona. A generic analytical procedure based on Soxhlet extraction followed by an automated cleanup system and gas chromatography-ion trap-mass spectrometry was employed for determining the toxic congeners of PCDDs and PCDFs, as well as dioxin-like PCBs. As regards PBDE determinations, a rapid method based on the use of selective pressurized liquid extraction followed by gas chromatography-negative ion chemical ionization-mass spectrometry was applied. Total toxicity equivalent (WHO-TEQ) values were calculated using the toxicity equivalent factors proposed by WHO for dioxin-like PCBs, PCDDs and PCDFs. WHO-TEQ values ranged from 0.3 to 75 pg/g dry weight (dw), with PCB contribution on the toxicity of the samples between 1 and 84%. Total PBDE levels ranged from 2.7 to 134 ng/g dw, with BDE-209 contribution on the total PBDE contamination between 50 and 99%.     

A Framework for Designing Ecological Monitoring Programs for Protected Areas: A Case Study of the Galachos del Ebro Nature Reserve (Spain)

The assessment of management effectiveness in protected areas, i.e., the evaluation of whether management strategies are actually helping to achieve stated goals, is becoming a priority. In any such evaluation, accurate information concerning the dynamics of the managed system is required—information that is gathered through monitoring. Few protected areas, however, have well-developed monitoring plans, and reserve managers are faced with a shortage of protocols for their design. This paper proposes a methodology, applicable to a wide range of situations, for designing such plans. The process begins with the precise definition of the aims of the monitoring plan, followed by the identification of key ecological processes and management objectives for the area, and finally the selection of a reduced set of indicators. These indicators are represented at three levels of growing complexity, allowing the plan to be followed in a modular fashion and in agreement with available resources.     

MODELING THE PERFORMANCE OF DEEP WASTE STABILIZATION PONDS1

ABSTRACT: The performance characteristics of a deep waste stabilization pond operating in Southeast Spain were studied for one year; the results show a high reduction in organic load and nutrients, as well as disinfection of the effluent, after a retention time that varies as a function of climatic conditions. Mathematical models describing its hydraulic, thermal, and biochemical bahavior are presented and compared with a set of measured data.     

DYNAMIC RESPONSE OF AQUIFER SYSTEMS TO LOCALIZED RECHARGE1

ABSTRACT. The response of stream-unconfined aquifer systems to localized recharge is investigated by means of a two-dimensional finite element model. A variational approach is used in conjunction with the finite element method to solve the ground water flow equation. Linear approximated triangular elements are used to calculate the hydraulic head distribution in the flow region. The Crank-Nicholson centered scheme of numerical integration is employed to approximate the time derivative in the flow equation. A computer program is developed to calculate the hydraulic head distribution in the flow region. Solutions provided by the finite element model should prove useful in the evaluation of quantitative and qualitative changes in aquifer systems due to natural or artificial recharge. In addition, they should prove useful in the study of irrigation and drainage problems.     

Effects of exposure to toxic and non-toxic dinoflagellates on oxygen consumption and locomotion in stage 1 larvae of the crabs Cancer oregonensis and C. magister

Sublethal effects on larval crabs upon exposure to toxic dinoflagellates were examined in the laboratory in early 1999. Specifically, oxygen consumption rates and geotaxis responses were determined for stage 1 larvae of the crabs Cancer oregonensis (Dana) and C. magister Dana that were exposed to non-toxic (Alexandrium tamarense, strain 115) or toxic (A. fundyense, strain 1719) dinoflagellates or to freshly hatched nauplii of the brine shrimp Artemia sp. In C. oregonensis, larvae exposed to the toxic dinoflagellate showed reduced rates of oxygen consumption compared to those exposed to non-toxic dinoflagellates or brine shrimp nauplii. Larvae exposed to a filtrate of the non-toxic dinoflagellate showed no change in oxygen consumption, but a reduced rate when exposed to filtrate from the toxic alga at densities >5᎒² cells ml^-1. In C. magister, larvae exposed to the non-toxic A. tamarense or the toxic A. fundyense had reduced oxygen consumption rates. Larvae exposed to filtrates of non-toxic and toxic dinoflagellates had no change in oxygen consumption. In geotaxis tests, C. oregonensis larvae exposed for 1 day to the toxic A. fundyense reduced their level of locomotion compared to those exposed to non-toxic A. tamarense or to brine shrimp nauplii. C. magister larvae showed no change in activity after a 1-day exposure to the toxic A. fundyense. After a 4-day exposure to A. fundyense, C. magister larvae had much reduced locomotion. Reduced locomotory activity in larvae exposed to toxic algae is consistent with the changes in oxygen consumption rates. Responding to exposure to toxic algae by reducing locomotion may affect vertical migration in these negatively buoyant crab larvae, resulting in sinking below a toxic alga bloom, at least temporarily.     

The Influence of Model Structure on Conclusions about the Viability and Harvesting of Serengeti Wildebeest

We investigate how the viability and harvestability predicted by population models are affected by details of model construction. Based on this analysis we discuss some of the pitfalls associated with the use of classical statistical techniques for resolving the uncertainties associated with modeling population dynamics. The management of the Serengeti wildebeest (Connochaetes taurinus) is used as a case study. We fitted a collection of age-structured and unstructured models to a common set of available data and compared model predictions in terms of wildebeest viability and harvest. Models that depicted demographic processes in strikingly different ways fitted the data equally well. However, upon further analysis it became clear that models that fit the data equally well could nonetheless have very different management implications. In general, model structure had a much larger effect on viability analysis (e.g., time to collapse) than on optimal harvest analysis (e.g., harvest rate that maximizes harvest). Some modeling decisions, such as including age-dependent fertility rates, did not affect management predictions, but others had a strong effect (e.g., choice of model structure). Because several suitable models of comparable complexity fitted the data equally well, traditional model selection methods based on the parsimony principle were not practical for judging the value of alternative models. Our results stress the need to implement analytical frameworks for population management that explicitly consider the uncertainty about the behavior of natural systems.