Percolation pond as a method of managed aquifer recharge in a coastal saline aquifer: A case study on the criteria for site selection and its impacts

Percolation ponds have become very popular methods of managed aquifer recharge due to their low cost, ease of construction and the participation and assistance of community. The objective of this study is to assess the feasibility of a percolation pond in a saline aquifer, north of Chennai, Tamil Nadu, India, to improve the storage and quality of groundwater. Electrical resistivity and ground penetrating radar methods were used to understand the subsurface conditions of the area. From these investigations, a suitable location was chosen and a percolation pond was constructed. The quality and quantity of groundwater of the nearby area has improved due to the recharge from the pond. This study indicated that a simple excavation without providing support for the slope and paving of the bunds helped to improve the groundwater quality. This method can be easily adoptable by farmers who can have a small pond within their farm to collect and store the rainwater. The cost of water recharged from this pond works out to be about 0.225 Re/l. Cleaning the pond by scrapping the accumulated sediments needs to be done once a year. Due to the small dimension and high saline groundwater, considerable improvement in quality at greater depths could not be achieved. However, ponds of larger size with recharge shafts can directly recharge the aquifer and help to improve the quality of water at greater depths.     

The crystal structure of disordered (Zr,Ti)O2 solid solution including srilankite: evolution towards tetragonal ZrO2 with increasing Zr

Crystal structure data are presented for seven synthetic samples of disordered zirconium-titanate solid solution (Zr,Ti)O₂, ranging in composition from x _Ti=0.43 to 0.67, thus covering compounds such as ZrTiO₄, Zr₅Ti₇O₂₄, and ZrTi₂O₆ (srilankite). The compounds, synthesized at high temperatures and various pressures in their respective stability fields, are well crystallized and of homogeneous composition. The resulting structure data are less scattered compared to previous studies that were based on compounds synthesized metastably at low temperatures and room pressure. The compounds have the structure of scrutinyite (α-PbO₂) with space group Pbcn, Z=4, unit cell parameters a=4.8495(3) Å, b=5.4635(3) Å, c=5.0462(3) Å at x _Ti=0.425 to a=4.7112(2) Å, b=5.4944(1) Å, c=4.9962(1) Å at x _Ti=0.666. The first structure refinement of pure, synthetic srilankite is presented, which is in good agreement with that of the natural counterpart. Structural trends observed in disordered zirconium-titanate solid solution along the binary join ZrO₂–TiO₂ are relatively smooth and continuous, except for rapid lengthening of an unshared octahedral edge which is anomalously short in scrutinyite-structure TiO₂. The shortness of this edge may explain the observed instability of this structure with the relatively small Ti as the dominant cation. With increasing Zr content, the average cation position moves off-centre inside the octahedron, away from two shared edges, which permits the 12 closest cation–cation distances in the structure to become more equal. The shortening of the b dimension with increasing amount of the larger cation Zr decreases the distance between octahedral Zr and two additional oxygens in an adjacent chain of edge-sharing octahedra, implying that the Zr environment is evolving towards eightfold coordination. If the two additional oxygens are considered as part of the Zr coordination polyhedron, the bonding topology of tetragonal zirconia is obtained. The compositional evolution of the cell parameters, Zr atomic coordinates and Zr coordination environment is consistent with the idea that the structure is evolving towards that of tetragonal ZrO₂. Group-theoretical relationships between scrutinyite, tetragonal zirconia, baddeleyite and fluorite structures show that the sequence of structures fluorite > tetragonal zirconia > scrutinyite > baddeleyite are all related by potentially diffusionless phase transitions driven by wavelike displacements of the oxygen substructure. The scrutinyite and tetragonal structures can act outside their stability fields as “transition states” between the structures on either side.     

Satellite bulk tropospheric temperatures as a metric for climate sensitivity

We identify and remove the main natural perturbations (e.g. volcanic activity, ENSOs) from the global mean lower tropospheric temperatures (T _LT ) over January 1979 - June 2017 to estimate the underlying, potentially human-forced trend. The unaltered value is +0.155 K dec^?1 while the adjusted trend is +0.096 K dec^?1, related primarily to the removal of volcanic cooling in the early part of the record. This is essentially the same value we determined in 1994 (+0.09 K dec^?1, Christy and McNider, 1994) using only 15 years of data. If the warming rate of +0.096 K dec^?1 represents the net T _LT response to increasing greenhouse radiative forcings, this implies that the T _LT tropospheric transient climate response (ΔT _LT at the time CO₂ doubles) is +1.10 ± 0.26 K which is about half of the average of the IPCC AR5 climate models of 2.31 ± 0.20 K. Assuming that the net remaining unknown internal and external natural forcing over this period is near zero, the mismatch since 1979 between observations and CMIP-5 model values suggests that excessive sensitivity to enhanced radiative forcing in the models can be appreciable. The tropical region is mainly responsible for this discrepancy suggesting processes that are the likely sources of the extra sensitivity are (a) the parameterized hydrology of the deep atmosphere, (b) the parameterized heat-partitioning at the oceanatmosphere interface and/or (c) unknown natural variations.     

The Hydraulic Profiling Tool for Hydrogeologic Investigation of Unconsolidated Formations

The hydraulic profiling tool (HPT) has become one of the basic tools for investigation of soils and unconsolidated formations over the last 10 years. The HPT is advanced into the subsurface using direct push methods. Clean water is injected into the formation from a small screened port on the side of the probe as it is steadily advanced into the subsurface. A downhole pressure sensor detects the pressure required to inject the water into the formation while an up-hole flowmeter monitors the water flow rate. An electrical conductivity (EC) array included in the lower end of the probe provides a simultaneous EC log of the bulk formation. The EC log, HPT pressure, and flow rate are logged and displayed onscreen as the probe is advanced. These logs enable the investigator to evaluate vertical changes in relative formation permeability at high resolution. Pressure dissipation tests may be performed at selected depths in coarse-grained materials to determine the piezometric pressure in saturated formations. This enables the operator to define the piezometric profile and determine the piezometric surface without a well. Post processing of the log in the viewing software provides for calculation of the corrected HPT pressure (Pc) and estimation of hydraulic conductivity (Est. K) within limits (~0.1 to 75 ft/d). In clean, coarse-grained materials the tandem EC log may be used to estimate groundwater specific conductance based on an Archie's Law model. Cross sections of HPT logs provide an efficient means to define hydrostratigraphy. When combined with contaminant logging tools such as the membrane interface probe (MIP) the HPT data may help to define contaminant migration pathways or contaminated low permeability zones that may result in back diffusion. The HPT can be a useful tool for many geoenvironmental investigations in unconsolidated formations.     

State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

Recently, near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy (Vib Spectrosc 54:42–49, 2010) to study and differentiate between free and hydrogen bonded silanol groups on silica gel surface. The method has given some insight into the type of functionalities, their location in silica gel samples, and the way the water molecules bind onto the silanol groups. The important information in this respect comes from the overtones of the OH groups of water molecules hydrogen-bonded to free silanol groups, and hydrogen-bonded silanol groups absorbing in the region 5,500–5,100 cm⁻¹. Chemically, opal minerals are hydrated silica and the same approach was adapted to study the state of water molecules, silanol functionalities, and their locations in opal samples from Slovakia. Twenty opal samples classified into CT and A classes and one quartz sample were used in this work. The samples were crushed using a hydraulic press and powderized. Each sample was then subjected to evacuation process to remove surface-adsorbed water at 200°C, and the near infrared spectrum of each sample was measured using a Perkin Elmer NTS FT-NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The samples were also heated to 750°C to remove the hydrogen-bonded silanol groups on the surface to reveal their locality. Second derivative profiles of the near infrared reflectance spectra were obtained using the instrument’s software and used in the detailed analysis of the samples. The analysis of the near infrared spectra and their second derivative profiles had the aim in finding relationships between the surface chemical structure and the classification of opal samples. The dry opal samples were also tested for their surface adsorption effectivity toward water molecules. The results indicate that the opal samples contain (1) surface-adsorbed water, (2) free and hydrogen-bonded silanol groups on the surface, (3) trapped water molecules in the bulk, and (4) free and hydrogen-bonded silanol groups in the cavity surfaces in the bulk. A part of the water molecules in the bulk of opal minerals are found as free molecules and the rest are found in hydrogen-bonded state to either free or vicinal or geminal silanol groups.     

Towards domestic fair trade? Farm labor, food localism, and the ‘family scale’ farm

Over the past several decades, consumers in the global North have increasingly looked to fair or alternative trading systems as a means to promote ecologically and socially sustainable agricultural production. While fair trade has historically been limited to international commodity networks, US-based agro-food activists have recently turned their attentions towards building a domestic movement, to bring fair trade principles and standards ‘home.’ Through an exploration of this growing movement, we consider the potential for third party certification and labeling to incorporate social justice into US-based agricultural production, with a particular focus on the implications for farm workers. We view current efforts to bring the principles of fair trade to the domestic arena as a reflection of several interrelated developments: a growing need on the part of small and mid-sized farmers to garner price premiums due to the erosion of the organic price premium; a recognition of the failure of organic certification to advance a holistic vision of sustainability; and the strategic embrace of voluntary regulatory mechanisms as an alternative to public regulation and collective bargaining. Initial research suggests that this has led to particular framings of the domestic fair trade concept, which may undermine the movement’s ability to address the social relations of agro-food production. Specifically, prioritization of the ‘family-scale’ farm and an undercurrent of food localism may obscure farm workers’ role in valorizing the US agricultural landscape.