The basin of Rio de la Sabana is the largest tributary of the Tres Palos coastal lagoon in Southwest Mexico, east of Acapulco. This lagoon and its upstream basin areas have become a high priority area for the preserva...The basin of Rio de la Sabana is the largest tributary of the Tres Palos coastal lagoon in Southwest Mexico, east of Acapulco. This lagoon and its upstream basin areas have become a high priority area for the preservation of coastal and marine environments. To obtain information about water quality as affected by urban expansion since 2002, fourteen physicochemical parameters (temperature, pH, electrical conductivity, dissolved oxygen, ammonium, nitrate, nitrite, sulphate, phosphate), biochemical (biological and chemical oxygen demand, methylene blue active substances) and bacteriological parameters (total and fecal coliforms) were determined. This sampling was done for dry and rainy season conditions at seven locations (S1, S2, S3, …, S7) along the river, spaced 3 to 6 km apart to a total of 30.4 km. The results were grouped into four zones: (Z1) reference, (Z2) transition, (Z3) polluted, (Z4) recovery. The Alborada (S5) and Tunzingo (S6) sites, adjacent to dense high-class residential areas (Z3), had the greatest pollution charges in both seasons, while the La Poza (S7) site near the Tres Palos lagoon (Z4) showed a decrease in pollution. All parameters correlated with increasing head- to down-river sampling distance by following linear (pH, DO) or curvilinear patterns (all other parameters). Using sampling location and dry versus rainy sampling season as multivariate regression (predictor) variables led to least-squares capturing: 1) 66% to 95% of the T(°C), pH, DO, and PO3-4 variations, and 2) 57% to 96% of the log-linear variations of the other parameters. Among the parameters, T(°C), DO, and PO3-4 were not significantly affected by sampling season, while pH became so after deleting two higher than usual pH values at the S5 and S6 locations during the dry season.展开更多
The main results of a study of pollen representation in surface soils from different plant communities in the upland savannas of Guayana were presented. The representation of savanna herb pollen mainly belonging to th...The main results of a study of pollen representation in surface soils from different plant communities in the upland savannas of Guayana were presented. The representation of savanna herb pollen mainly belonging to the Poaceae and Cyperaceae was high in open communities such as fernlands, grasslands and Mauritia palm swamps, but decreased as vegetation structure became more closed and woody;from savanna-forest borders to secondary forests and lastly, evergreen montane forests;mimicking the gradient of vegetation openness observed in living plant communities. Thus, the proportion of savanna herb pollen in herbaceous communities: swamps, fernlands and grasslands, reached over 80% and arboreal pollen contributed less than 10%. This ratio changed in savanna-forest borders where savanna herb pollen decreased to 60% or less and the proportion of arboreal pollen rose to 30% or higher. Lastly, in forest soils, pollen abundances from trees (Dimorphandra, Protium, Schefflera), shrubs (Miconia and other Melastomataceae) and lianas contributed higher than 60% of the pollen sum, even in open gallery forests and fallows. The lack of pollen from cassava, the main crop in the forests of the region, at these sites was remarkable. The ordination of sediment samples from 4 records from the Late Holocene with respect to the soil surface samples studied, showed that the characterization of pollen rain was useful for identifying long-term compositional and structural changes in the sedimentary records, thus providing objective indicators for the interpretation of past vegetation structure.展开更多
文摘The basin of Rio de la Sabana is the largest tributary of the Tres Palos coastal lagoon in Southwest Mexico, east of Acapulco. This lagoon and its upstream basin areas have become a high priority area for the preservation of coastal and marine environments. To obtain information about water quality as affected by urban expansion since 2002, fourteen physicochemical parameters (temperature, pH, electrical conductivity, dissolved oxygen, ammonium, nitrate, nitrite, sulphate, phosphate), biochemical (biological and chemical oxygen demand, methylene blue active substances) and bacteriological parameters (total and fecal coliforms) were determined. This sampling was done for dry and rainy season conditions at seven locations (S1, S2, S3, …, S7) along the river, spaced 3 to 6 km apart to a total of 30.4 km. The results were grouped into four zones: (Z1) reference, (Z2) transition, (Z3) polluted, (Z4) recovery. The Alborada (S5) and Tunzingo (S6) sites, adjacent to dense high-class residential areas (Z3), had the greatest pollution charges in both seasons, while the La Poza (S7) site near the Tres Palos lagoon (Z4) showed a decrease in pollution. All parameters correlated with increasing head- to down-river sampling distance by following linear (pH, DO) or curvilinear patterns (all other parameters). Using sampling location and dry versus rainy sampling season as multivariate regression (predictor) variables led to least-squares capturing: 1) 66% to 95% of the T(°C), pH, DO, and PO3-4 variations, and 2) 57% to 96% of the log-linear variations of the other parameters. Among the parameters, T(°C), DO, and PO3-4 were not significantly affected by sampling season, while pH became so after deleting two higher than usual pH values at the S5 and S6 locations during the dry season.
文摘The main results of a study of pollen representation in surface soils from different plant communities in the upland savannas of Guayana were presented. The representation of savanna herb pollen mainly belonging to the Poaceae and Cyperaceae was high in open communities such as fernlands, grasslands and Mauritia palm swamps, but decreased as vegetation structure became more closed and woody;from savanna-forest borders to secondary forests and lastly, evergreen montane forests;mimicking the gradient of vegetation openness observed in living plant communities. Thus, the proportion of savanna herb pollen in herbaceous communities: swamps, fernlands and grasslands, reached over 80% and arboreal pollen contributed less than 10%. This ratio changed in savanna-forest borders where savanna herb pollen decreased to 60% or less and the proportion of arboreal pollen rose to 30% or higher. Lastly, in forest soils, pollen abundances from trees (Dimorphandra, Protium, Schefflera), shrubs (Miconia and other Melastomataceae) and lianas contributed higher than 60% of the pollen sum, even in open gallery forests and fallows. The lack of pollen from cassava, the main crop in the forests of the region, at these sites was remarkable. The ordination of sediment samples from 4 records from the Late Holocene with respect to the soil surface samples studied, showed that the characterization of pollen rain was useful for identifying long-term compositional and structural changes in the sedimentary records, thus providing objective indicators for the interpretation of past vegetation structure.
