Seasonal variation in natural recharge of coastal aquifers

Many coastal zones around the world have irregular precipitation throughout the year. This results in discontinuous natural recharge of coastal aquifers, which affects the size of freshwater lenses present in sandy deposits. Temperature data for the period 1960–1990 from LocClim (local climate estimator) and those obtained from the Intergovernmental Panel on Climate Change (IPCC) SRES A1b scenario for 2070–2100, have been used to calculate the potential evapotranspiration with the Thornthwaite method. Potential recharge (difference between precipitation and potential evapotranspiration) was defined at 12 locations: Ameland (The Netherlands), Auckland and Wellington (New Zealand); Hong Kong (China); Ravenna (Italy), Mekong (Vietnam), Mumbai (India), New Jersey (USA), Nile Delta (Egypt), Kobe and Tokyo (Japan), and Singapore. The influence of variable/discontinuous recharge on the size of freshwater lenses was simulated with the SEAWAT model. The discrepancy between models with continuous and with discontinuous recharge is relatively small in areas where the total annual recharge is low (258–616 mm/year); but in places with Monsoon-dominated climate (e.g. Mumbai, with recharge up to 1,686 mm/year), the difference in freshwater-lens thickness between the discontinuous and the continuous model is larger (up to 5 m) and thus important to consider in numerical models that estimate freshwater availability

Fracture patterns and fault development in the pelagic limestones of the Monte Conero Anticline (Italy)

Fracture patterns reflect the tectonic history of an area. By studying the characteristics of fracture patterns in outcrops it is feasible to reconstruct the sequence of events which helps to predict the fracture patterns in similar geological settings including fractured reservoirs and aquifers. This paper studies the fracture assemblages exposed in outcrops of the Monte Conero anticline, formed by two principal carbonate formations: the Maiolica and the Scaglia Rossa. Fieldwork measurements of fracture properties such as, orientation, length, aperture, microscope analysis of thin sections and crosscutting relationships, led to the recognition of a sequence of events and a fault development model that can explain the occurrence and morphology of breccia zones. The fractures occurring in the outcrops of Monte Conero, consist of veins, stylolites, joints, faults with breccias that occur both in elongated zones and in pockets. Veins and stylolites are the most occurring fractures and the highest fracture density occurs in outcrops along the coastline. Veins and stylolites are arranged in various geometries (e.g. en-echelon) which influence the connectivity with other fractures. Veins and stylolites play a fundamental role in the fault development process. Maiolica and Scaglia Rossa Fm. show different processes of fault development. The initial phase of fault development consists in both formations by shearing along pre-existing veins and the connection of veins by tail-joints. These tail joints break up the rock in between overlapping segments of sheared veins. In the Maiolica Fm, both joints and stylolites form at the tip of faults. The discontinuities at the tip of the faults are explained by high local stress concentrations. The relationships between fracture types observed at the micro-scale are similar to the ones observed at the outcrop-scale. Three different geological episodes were identified and each one is associated to a rotation of the directions of the principal stresses, the first episode formed a set of veins at high angle to bedding, the second episode formed sets of stylolites and the third episode caused slip along the pre-existing veins with formation of new sets of veins, stylolites, and breccia. The fault development process in Monte Conero is related to large and local scale tectonic events during which the veins, stylolites, joints and faults were formed and connected at different stages of the folding process, generating breccia zones. Breccia zones in faults are the only structures that contribute substantially to the secondary porosity of the low-porosity Conero's carbonate rocks

The effect of saline gravel pit lakes (Ravenna, Italy) on groundwater chemistry

The hydrochemistry of gravel pit lakes excavated into Holocene beach gravel deposits near the Adriatic Coast of Emilia Romagna (Italy) was studied to determine the influence of these lakes on water and chemical budgets of the aquifer

Seasonal dynamic of a shallow freshwater lens due to irrigation in the coastal plain of Ravenna, Italy

Irrigation in low-lying coastal plains may enhance the formation of fresh groundwater lenses, which counteract salinization of groundwater and soil. This study presents seasonal dynamics of such a freshwater lens and discusses its influence on the salinity distribution of the unconfined aquifer in the coastal plain of Ravenna, Italy, combining field observations with numerical modeling (SEAWAT). The lens originates from an irrigation ditch used as a water reservoir for spray irrigation. The geometry of the freshwater lens shows seasonal differences because of freshwater infiltration during the irrigation season and upconing of deeper saltwater for the remainder of the year. The extent of the freshwater lens is controlled by the presence of nearby drainage ditches. Irrigation also results in a temperature anomaly in the aquifer because of the infiltration of warm water during the irrigation season. The surficial zone in the vicinity of the irrigation ditch is increased considerably in thickness. Finally, different irrigation alternatives and the influence of sea-level rise are simulated. This shows that it is necessary to integrate irrigation planning into the water management strategy of the coastal zone to have maximum benefits for freshening of the aquifer and to make optimal use of the existing infrastructure

Groundwater Freshening Following Coastal Progradation and Land Reclamation of the Po Plain, Italy

Many coastal areas historically were inundated by seawater, but have since undergone land reclamation to enable settlements and farming. This study focuses on the coastal unconfined aquifer in the Po Plain near Ravenna, Italy. Fresh water is present as isolated, thin (1-5 m) lenses on top of brackish-salt water. Historical maps show large areas of sea inundation until approximately 150-200 years ago when coastal progradation and construction of the drainage canals began. Since then, the aquifer has been freshening from recharge. A 3D SEAWAT model is used to simulate a 200 year freshening history, starting with a model domain that is saturated with sea water, and applying recharge across the top model layer. Calibration to the observed concentrations is remarkably good for discrete depths within many monitoring wells despite model simplicity. The distribution of fresh water at the end of the 200 year period, representing current conditions, is controlled by the drainage network. Within and adjacent to the drains, the groundwater has high salinity due to up-coning of salt water. Between drains, the surface layers of the aquifer are fresh due to the flushing action of recharge. The modeling results are consistent with cation exchange processes revealed in the groundwater chemistry

A highly virulent variant of HIV-1 circulating in the Netherlands

We discovered a highly virulent variant of subtype-B HIV-1 in the Netherlands. One hundred nine individuals with this variant had a 0.54 to 0.74 log10 increase (i.e., a ~3.5-fold to 5.5-fold increase) in viral load compared with, and exhibited CD4 cell decline twice as fast as, 6604 individuals with other subtype-B strains. Without treatment, advanced HIV-CD4 cell counts below 350 cells per cubic millimeter, with long-term clinical consequences-is expected to be reached, on average, 9 months after diagnosis for individuals in their thirties with this variant. Age, sex, suspected mode of transmission, and place of birth for the aforementioned 109 individuals were typical for HIV-positive people in the Netherlands, which suggests that the increased virulence is attributable to the viral strain. Genetic sequence analysis suggests that this variant arose in the 1990s from de novo mutation, not recombination, with increased transmissibility and an unfamiliar molecular mechanism of virulence