Methodology for groundwater recharge assessment in carbonate aquifers: application to pilot sites in southern Spain

Aquifer recharge can be determined by conventional methods such as hydrodynamic or hydrologic balance calculations, or numerical, hydrochemical or isotopic models. Such methods are usually developed with respect to detrital aquifers and are then used on carbonate aquifers without taking into consideration their hydrogeological particularities. Moreover, such methods are not always easy to apply, sometimes requiring data that are not available. Neither do they enable determination of the spatial distribution of the recharge. For eight regions in southern Spain, the APLIS method has been used to estimate the mean annual recharge in carbonate aquifers, expressed as a percentage of precipitation, based on the variables altitude, slope, lithology, infiltration landform, and soil type. The aquifers are representative of a broad range of climatic and geologic conditions. Maps of the above variables have been drawn for each aquifer, using a geographic information system; thus they can be superimposed to obtain the mean value and spatial distribution of the recharge. The recharge values for the eight aquifers are similar to those previously calculated by conventional methods and confirmed by discharge values, which corroborates the validity of the method.     

TPH and PAH concentrations in the subsoil of polyduct segments, oil pipeline pumping stations, and right-of-way pipelines from Central Mexico

For the year 1996, 366 incidents related with clandestine poaching of oil-products were reported in Mexico, 159 in 1997, and 240 in 1998. For the year 2003 (the most recently reported figure), there were 136 events. Petroleos Mexicanos (PEMEX), very concerned with the environmental agenda, has developed programs oriented to diminish contamination levels in all of its oil facilities. This work was aimed at characterizing zones around polyduct segments, pipelines, pumping stations, and right-of-way pipelines located in the center of Mexico. The TPH contaminated sites were, in decreasing order, polyduct km 39 + 150 > polyduct km 25 + 020 > Zoquital > Tepetitlan > Catalina > Venta Prieta > Ceiba. Most of the sampled points showed the presence of more than one of the 16 PAHs considered by USEPA as priority pollutants. Except point TEPE 2A, where no PAHs were detected, all the sampled points showed values from low to medium concentrations; however, values found at the sites did not exceed the limits according to the Mexican or the American legislation. The place with the largest contaminated area corresponded to the polyduct km 39 + 150, with 130 m² and 260 m³ to be treated. The least contaminated area was that around the JUAN 4 point at Juandho station, with 20 m² and 22 m³ of contaminated soil. The total area to be treated is about 230 m² and 497 m³.     

The structure and function of dry weather mangroves on the Pacific Coast of Central America,with emphasis onAvicennia bicolor forests

Mangrove forests along the Pacific Coast of Central America cover around 4,000 km². Most of this coast is occupied with tropical dry forest mangroves where basal areas range between 6 and 20 m² ha^?1 and canopy heights rarely exceed 20 m. Rainfall and runoff alter structure and floristic composition from site to site. Reproductive phenology and mortality appear to be related to soil water availability.Avicennia bicolor forests reach a density of 4,350 plants that are taller than 0.50 m ha^?1, with 769 trees above 5 cm diameter at breast height A total basal area of 41 m² ha^?1 together with a canopy height of about 23 m place these forests among the most developed in the western hemisphere. Growth rate (0.38 m² ha^?1 yr^?1) is surprisingly high for mangrove forests under a seasonal dry climate.     

Evaluation of seismic hazard at Roermond, The Netherlands: A comparison of results after the 13 April 1992 earthquake

Mean return periods, RP, for the site of Roermond, The Netherlands, as calculated by different methods, are compared, and its quality evaluated by a simple two-tail test of hypothesis. Results show that RP values by the EGO-method are statistically more likely. They can be considered, despite their broad 90% probability intervals, and for the site and data used, more reliable, since the Roermond earthquake was not an unusual or surprising event for the Lower Rhine Embayment area, where earthquakes of comparable size have occurred since the 18th century.     

Submerged vegetation complexity modifies benthic infauna communities: the hidden role of the belowground system

Marine plants provide a variety of functions with high economic and ecological values in ecosystems. The above‐ (AG) and below‐ground (BG) systems increase the structural complexity of plants, which also enhance faunal abundance and diversity. The ecological role of the AG compartment in structuring inter‐tidal macrobenthic communities has been widely studied; however, this is not the case for the BG compartment. This study addressed the effects of variation in vegetation complexity (in both AG and BG systems) on associated macrobenthic infauna with respect to abundance, species richness, composition, weight and body type. To achieve this aim, a field experiment using artificial vegetation mimics was carried out using replicated treatments with different AG‐BG complexity ratios. We found a significant increase in the density and the number of taxa of macrobenthic infaunal species in plots with vegetation mimics compared with unvegetated areas, regardless of either AG or BG complexity. This effect was found even when AG parts were not present (i.e. when only BG parts were used). Furthermore, a positive relationship between structural complexity and diversity was recorded. Variation in one or both plant compartments was strongly related to diversity changes in the associated macrobenthic infauna. In conclusion, our experimental set‐up provides the first evidence that the BG compartment is at least as important as the AG compartment in controlling diversity in inter‐tidal vegetated areas because it was able to strongly affect community structure even when the AG system was totally absent.     

Quartz-grain shape: A record of the source of fine-grained sediments

The traditional petrographic means of determining the source of sediments, namely, heavy mineral analysis, is not easily practiced on fine-grained sediments. As a result, we have little information about the sources of muds, the most common sediment in the stratigraphic record.The shapes of quartz grains are also a record of their source. There have been a number of studies that have applied shape analysis to the problem of identifying the sources of sand. In this report, we extend this sourcing approach to fine-grained sediments in a study of the sources of silt on the South Texas Shelf.     

Groundwater response to tidal fluctuations in a leaky confined coastal aquifer with a finite length

The study on the hydraulic properties of coastal aquifers has significant implications both in hydrological sciences and environmental engineering. Although many analytical solutions are available, most of them are based on the same basic assumption that assumes aquifers extend landward semi‐infinitely, which does not necessarily reflect the reality. In this study, the general solutions for a leaky confined coastal aquifer have been developed that consider both finitely landward constant‐head and no‐flow boundaries. The newly developed solutions were then used to examine theoretically the joint effects of leakage and aquifer length on hydraulic head fluctuations within the leaky confined aquifer, and the validity of using the simplified solution, which assumes the aquifer is semi‐infinite. The results illustrated that the use of the simplified solution may cause significant errors, depending on joint effects of leakage and aquifer length. A dimensionless characteristic parameter was then proposed as an index for judging the applicability of the simplified solution. In addition, practical application of the general solution for the constant‐head inland boundary was used to characterize the hydraulic properties of a leaky confined aquifer using the data collected from a field site at the Seine River estuary, France, and the versatility of the general solution was further justified.