Comparisons of WRF/Chem simulated O3 concentrations in Mexico City with ground-based RAMA measurements during the MILAGRO period

This work compares the WRF/Chem (Weather Research and Forecasting – Chemistry) simulated O₃ concentrations in the Mexico City Metropolitan Area (MCMA) with measurements from the ground-based RAMA network during the MILAGRO (Megacity Initiative: Local and Global Research Observations) period. The model resolves the observations reasonably well in terms of diurnal cycle and mean magnitude as reflected by high correlation coefficients and low root-mean-square errors. Stations located in the center of the MCMA generally exhibit higher correlation coefficients and lower model biases than those stations located in the peripheral of the MCMA. Large temporal variations in the observed and simulated O₃ concentrations are noted from station to station during the MILAGRO period. Sensitivity analyses of O₃ concentrations to changes in NO_x and VOC emissions rates suggest that O₃ production in the MCMA is VOC-sensitive, and VOC-emissions reduction appears to be an effective strategy for reducing high surface O₃ concentrations in the MCMA.     

Estimating the Ecological Condition of the Estuaries of the Gulf of Mexico

Monitoring of estuaries in the Louisianian Province was performed annually from 1991–1994 to assess ecological conditions on a regional scale. We found over the four years of monitoring, 25±6% of Gulf of Mexico estuarine sediments in the Louisianian Province displayed poor biological conditions, as measured by benthic community structure, and 14±7% of the area was characterized by poor water clarity, the presence of marine debris, and elevated levels of fish tissue contaminants. Using statistical associations to discern relationships between ecological condition and exposure or stressor data has shown that much of this degraded' condition co-occurs with sediment contamination.     

Air Emissions Assessment from Offshore Oil Activities in Sonda de Campeche, Mexico

Air emission data from offshore oil platforms, gas and oil processing installations and contribution of marine activities at the Sonda de Campeche, located at the Gulf of Mexico, were compiled and integrated to facilitate the study of long range transport of pollutants into the region. From this important region, roughly 76% of the total Mexican oil and gas production is obtained. It was estimated that the total air emissions of all contaminants are approximately 821,000 tons per year. Hydrocarbons are the largest pollutant emissions with 277,590 tons per year, generated during flaring activities, and SOx in second place with 185,907 tons per year. Marine and aviation activities contribute with less than 2% of total emissions. Mass of pollutants emitted per barrel of petroleum produced calculated in this work, are in the range reported by similar oil companies.     

Distribution of mercury in adult penaeid shrimps from Altata-Ensenada del Pabellón lagoon (SE Gulf of California)

The Altata-Ensenada del Pabellón lagoon system is located in the central part of Sinaloa state, NW Mexico. The major sources of pollution are represented by the waste effluents from the intensive agriculture and the urban sewage from the cities of Culiacán (population of 750 000) and Navolato (population of 50 000). In this lagoon system diverse penaeid shrimps occur; the crystal shrimp Farfantepenaeus brevirostris, the brown shrimp F. californiensis, the blue shrimp Litopenaeus stylirostris, the white shrimp L. vannamei and the Pacific seabob Xiphopenaeus kroyeri. With the purpose of knowing distribution and relative concentrations of Hg in the main tissues of penaeid shrimps, levels of Hg in five species from Altata-Enesenada del Pabellón lagoon on the SE Gulf of California were determined. Analysis were carried out by reducing mercury compounds after acid digestion reduction with SnCl₂ and detection by cold vapour atomic absorption. In general, hepatopancreas was the tissue where Hg was mostly accumulated, followed by muscle and exoskeleton. The sequence of Hg concentrations in the five species studied here for every tissue was: hepatopancreas L. vannamei > F. californiensis > L. stylirostris > F. brevirostris > X. kroyeri; muscle L. stylirostris > F. brevirostris > L. vannamei > F. CALIFORNIENSIS=X. kroyeri and exoskeleton F. brevirostris > F. californiensis > L. vannamei > L. stylirostris > X. kroyeri.     

NUTRIENT AND HEAVY METAL TRANSPORT CAPABILITIES OF SEDIMENT IN THE SOUTHWESTERN UNITED STATES1

ABSTRACT: Most studies of nutrient loss from small study watersheds ignore a potentially important loss transported by the suspended sediment load. We proposed that the geology and vegetation of a watershed are predictors of the nutrient and heavy metal transporting capacity of its suspended sediment. Analyses of acid-digestable and extractable nutrients showed differences for sediments derived from ponderosa pine forests in the Southwest on different geologies. These differences were similar for soil, stream bank, and stream channel material for a given site. Suspended sediment collections had nutrient concentrations similar to those of stream channel collections. Different vegetation on a given geology affected primarily the organic matter content, cation exchange capacity, total P, and levels of extractable nutrients in sediment.     

Communication Strategy of Transboundary Air Pollution Findings in a US–Mexico Border XXI Program Project

From 1996 to 1997, the US Environmental Protection Agency (EPA) and the Texas Natural Resource Conservation Commission (TNRCC) conducted an air quality study known as the Lower Rio Grande Valley Transboundary Air Pollution Project (TAPP). The study was a US–Mexico Border XXI program project and was developed in response to local community requests on a need for more air quality measurements and concerns about the health impact of local air pollutants; this included concerns about emissions from border-dependent industries in Mexico, known as maquiladoras. The TAPP was a follow-up study to environmental monitoring done by EPA in this area in 1993 and incorporated scientific and community participation in development, review of results, and public presentation of findings. In spite of this, critical remarks were leveled by community activists against the study's preliminary “good news” findings regarding local air quality and the influence of transboundary air pollution. To resolve these criticisms and to refine the findings to address these concerns, analyses included comparisons of daily and near real-time measurements to TNRCC effects screening levels and data from other studies along with wind sector analyses. Reassessment of the data suggested that although regional source emissions occurred and outliers of elevated pollutant levels were found, movement of air pollution across the border did not appear to cause noticeable deterioration of air quality. In spite of limitations stated to the community, the TAPP was presented as establishing a benchmark to assess current and future transboundary air quality in the Valley. The study has application in Border XXI Program or other air quality studies where transboundary transport is a concern since it involved interagency coordination, public involvement, and communication of scientifically sound results for local environmental protection efforts.     

Long-term climate variability at the Waste Isolation Pilot Plant,southeastern New Mexico,USA

The United States Department of Energy is developing the Waste Isolation Pilot Plant (WIPP) in southeastern New Mexico for the disposal of transuranic wastes generated by defense programs. Because changes in climate during the next 10,000 years (10 ka) may affect performance of the repository, an understanding of long-term climate variability is essential for evaluating regulatory compliance. Fluctuations in global climate corresponding to glaciation and deglaciation of the northern hemisphere have been regular in both frequency and amplitude for at least 780 ka. Coolest and wettest conditions in the past have occurred at the WIPP during glacial maxima, when the North American ice sheet reached its southern limit roughly 1200 km north of the WIPP and deflected the jet stream southward. Average precipitation in southeastern New Mexico during the last glacial maximum 22-18 ka before present (BP) was approximately twice that of the present. Driest conditions (precipitation approximately 90% of present) occurred 6.5-4.5 ka BP, after the ice sheet had retreated to its present location. Wet periods of unknown duration have occurred since the retreat of the ice sheet, but none have exceeded glacial conditions. Global climate models suggest that anthropogenic climate changes (i.e., warming caused by an increased greenhouse effect) will not result in an increase in precipitation at the WIPP. The climate of the last glacial maximum is therefore suitable for use as a cooler and wetter limit for variability during the next 10 ka.     

Consequences of Buffelgrass Pasture Development for Primary Productivity,Perennial Plant Richness,and Vegetation Structure in the Drylands of Sonora,Mexico

Abstract: In large parts of northern Mexico native plant communities are being converted to non‐native buffelgrass (Pennisetum ciliare) pastures, and this conversion could fundamentally alter primary productivity and species richness. In Sonora, Mexico land conversion is occurring at a regional scale along a rainfall‐driven gradient of primary productivity, across which native plant communities transition from desert scrub to thorn scrub. We used a paired sampling design to compare a satellite‐derived index of primary productivity, richness of perennial plant species, and canopy‐height profiles of native plant communities with buffelgrass pastures. We sampled species richness across a gradient of primary productivity in desert scrub and thorn scrub vegetation to examine the influence of site productivity on the outcomes of land conversion. We also examined the influence of pasture age on species richness of perennial plants. Index values of primary productivity were lower in buffelgrass pastures than in native vegetation, which suggests a reduction in primary productivity. Land conversion reduced species richness by approximately 50% at local and regional scales, reduced tree and shrub cover by 78%, and reduced canopy height. Land conversion disproportionately reduced shrub species richness, which reflects the common practice among Sonoran ranchers of conserving certain tree and cactus species. Site productivity did not affect the outcomes of land conversion. The age of a buffelgrass pasture was unrelated to species richness within the pasture, which suggests that passive recovery of species richness to preconversion levels is unlikely. Our findings demonstrate that land conversion can result in large losses of plant species richness at local and regional scales and in substantial changes to primary productivity and vegetation structure, which casts doubt on the feasibility of restoring native plant communities without active intervention on the part of land managers.     

The relationship of social capital and fishers’ participation in multi-level governance arrangements

The need for effective multi-level governance arrangements is becoming increasingly urgent because of complex functional interdependencies between biophysical and socioeconomic systems. We argue that social capital plays an important role in such systems. To explore the relationship between social capital and participation in resource governance arenas, we analyzed various small-scale fisheries governance regimes from the Gulf of California, Mexico. The components of social capital that we measured include levels of fishers’ structural ties to relevant groups and levels of trust in different entities (i.e. cognitive component). We collected data using surveys and interviews with residents of small-scale fishing communities adjacent to marine protected areas. We analyzed the data using a logistic regression model and narrative analysis. The results of our quantitative analysis highlight the multidimensional nature of social capital and reveals complex relationships between different types of social capital and fisher participation in monitoring, rulemaking and MPA design. Furthermore our qualitative analysis suggests that participation in fisheries conservation and management is not fully potentialized due to the social and historical context of participatory spaces in Mexico.