Groundwater Complexity in Urban Catchments: Shenzhen,Southern China

Groundwater interactions with surface water and sewers in an urban setting are complex, and classic hydrogeological approaches must be combined with anthropogenic elements to characterize them. The level of detail needed to understand these interactions is illustrated by the analysis of an urban subcatchment in the megacity of Shenzhen in southern China that has had a drastic urban expansion in the last 40 years. The study area is characterized by the Yanshanian granite that is widespread across southern-eastern China. The urban setting is studied using multitemporal analysis of satellite images, borehole investigations and field surveys. Given the local hydrostratigraphy, a conceptual model was developed to identify the physical and anthropogenic factors that regulate the urban groundwater system. Based on the conceptual model and the data collected from the field or compiled from the literature, the average annual effective recharge is estimated to be 290 mm/year, after the urbanization process. From rural to urban conditions, it is estimated that the effective recharge increased by 170% and sewers intercept at least 23% of the effective recharge. Groundwater captured by sewers reduces river flows and increases the required capacity and costs for waste water treatment plants.     

Potential nitrate leaching to groundwater from house building

Nitrate pollution has been identified as a major water quality issue in the UK. This study aimed to determine the potential additional loading of nitrate that could arise from the disturbance caused by house construction. The study is centred around the towns of Nottingham and Mansfield, UK, which are situated on a Triassic Sandstone aquifer. Soil samples up to a depth of 2·70 m were taken from seven sites under construction and other land uses. The average nitrogen load was 59 kg ha^?1, which is slightly higher than the nitrate leaching observed when temporary grassland is ploughed in temperate climates. The most important factors involved in nitrogen loss from house building are expected to be previous land use, quantity of total nitrogen after topsoil stripping, and seasonal timing of construction. Copyright © 2006 John Wiley & Sons, Ltd.     

Adaptive capacity in evolving peri-urban spaces: Responses to flood risk in the Upper Lerma River Valley,Mexico

Although ‘peri-urban’ and ‘rur-urban’ growth patterns are now prominent in previously rural areas of Latin America, there has been little exploration of the implication of these patterns for social vulnerability to hazards and adaptive capacity for hazard management. A case study of flooding in the Upper Lerma River Valley, Mexico, illustrates how livelihood and land use change in these peri-urban spaces have altered residents’ perceptions of risk and loss, while public officials are adhering to a traditional sectoral and structural interpretation of flooding as an agricultural problem, managed by agricultural and water agencies. The current system of treating flooding as an agricultural problem, managed by agricultural and water agencies, does not address the increased role of urbanization as a driver of flooding and water risk in the valley. The resulting mismatch in policy potentially exacerbates regional vulnerability in face of rising flood losses. Enhancing adaptive capacity in this context requires a new vision of the populations and communities of the region as an integrated system, supported by institutions that facilitate cross-scale and intersectoral planning.     

Asexual origin of brooding in the sea anemones Actinia equina and A. schmidti: molecular evidence from the Portuguese shore

Reproduction by sexual or asexual viviparity is a common phenomenon in some anemone species. In this short communication, the origin of the brooded young of Actinia equina and A. schmidti from the Portuguese shore was investigated. DNA was extracted from 56 brooding adult Actinia sp. and the nuclear gene that codes for the 28S ribosomal subunit was sequenced. Species identity was then assessed using GenBank. In total, 50 individuals were A. schmidti, five were A. equina and one had a hybrid origin. Three adult anemones (the hybrid, one A. equina and one A. schmidti) possessed two different 28S sequences and so their offspring was selected for further analysis using the same molecular procedure. Each brooded polyp was found to possess the exact same sequence as its parent, strongly suggesting the asexual origin of broods in A. equina and A. schmidti.     

Experimental and Modelling Approaches for the Assessment of Chemical Impacts of Leachate Migration from Landfills: A Case Study of a Site on the Triassic Sandstone Aquifer in the UK East Midlands

Current risk-based methods for assessing the effects of landfill leachate migration on groundwater resources are conservative and generalised. Cost-effective and practical strategies are required which can robustly determine the potential for contaminant attenuation on a site-specific basis. In this paper laboratory column experiments and reactive transport modelling are evaluated as a combined approach for assessing the chem’ical impact of leachate migration in the Triassic Sandstone aquifer. The results are compared with field data for a landfill in the East Midlands. Columns of aquifer sandstone were flushed sequentially with groundwater, followed by acetogenic or methanogenic leachate to simulate chemical interactions occurring during leachate loading episodes. The key contaminants in leachate (NH₄, heavy metals, organic fractions) were attenuated by ion exchange, redox reactions, sorption and degradation. These processes produce a consistent hydrochemical signature which may help identify the extent of leachate migration in the aquifer. The laboratory results largely replicate those found in the field system, and the behaviour of inorganic contaminants during leachate flushing of the aquifer columns can be described by the reactive transport model. The experimental and modelling approach presented represents a powerful tool for risk assessment and prediction of leachate contaminant fate at unlined and lined landfills.     

Quantitative seafloor characterization using a bathymetric sidescansonar

Bathymetry and backscatter measurements from a 120-kHz phase-difference sonar are analysed in terms of statistical and spectral characteristics. Data from a multisensor, multiscale survey of the Juan de Fuca Ridge are compared across three distinct geological provinces: sediment pond, ridge flank, and axial valley. The detrended bathymetry follows a Gaussian distribution; the power spectral density can be approximately described by a power law. The composite multiscale power spectrum demonstrates a similar slope spanning a spatial frequency range from about 0.005 to 50 cycles/m, corresponding to a range of geological features from a few hundred meters down to several centimeters. The backscattering strength and grazing-angle dependencies agree with previous empirical studies; data from a sediment-pond region are shown to match theoretical predictions of the composite-roughness model. Histograms of the echo amplitude are characterized by a multimodal Rayleigh probability density function. For all analyses, the data show distinct differences among the three provinces     

The Strecker synthesis as a source of amino acids in carbonaceous chondrites: deuterium retention during synthesis

Deuterium-enriched amino acids occur in the Murchison carbonaceous chondrite. Synthesis from D-enriched interstellar precursors by Strecker reactions during aqueous alteration of the parent body has been proposed. To test this hypothesis, we have measured the retention of deuterium in amino acids produced from HCN, NH3, and formaldehyde-D2, acetaldehyde-D4, and acetone-D6 in H2O. The isotopic label is 50% to 98% retained, with variations in retentivity depending on the amino acid and the reaction conditions. If amino acids, once formed on the parent body by the Strecker synthesis, lose no deuterium by subsequent exchange with water or H-bearing minerals, then the observed deuterium isotopic composition of Murchison amino acids represents as much as 50% or more of the enrichments inherited from their interstellar precursors. Imino diacids are prominent side products of the Strecker synthesis which have not been reported in carbonaceous chondrites. Under the conditions of the Strecker reaction using deuterium labeled aldehydes and ketones, unlabeled amino acids are also formed by an HCN polymerization route indicating multiple pathways for the synthesis of amino acids in meteorites.