Planning Urban Growth in Ground Water Recharge Areas: Central Valley, Costa Rica

Nitrate levels in the ground water of the Central Valley of Costa Rica have increased in relation to the past. Previous studies determined that the unseweved sanitation systems in the recharge areas are the main source of nitrogen. Calculations are made in this study to estimate the maximum population density allowable without improved sewage systems in order to keep the nitrogen levels in ground water below the World Health Organization (WHO) criteria. Results were achieved employing a mass balance that involved the concentration and rate of domestic effluents and the flow rate in the aquifer, as well as an estimation of the effects caused by the agricultural activity. It was concluded that, in general terms, the population density must not exceed 45 inhabitants per hectare. Otherwise, sewage systems and treatment plants are necessary. These conclusions provide a basis for urban growth planning, which will protect ground water quality. The method used in this case should apply to similar situations.     

The structure of the lower crust at the Argentine continental margin, South Atlantic at 44°S

It is well established that the Argentine passive margin is of the rifted volcanic margin type. This classification is based primarily on the presence of a buried volcanic wedge beneath the continental slope, manifested by seismic data as a seaward dipping reflector sequence (SDRS). Here, we investigate the deep structure of the Argentine volcanic margin at 44°S over 200 km from the shelf to the deep oceanic Argentine Basin. We use wide-angle reflection/refraction seismic data to perform a joint travel time inversion for refracted and reflected travel times. The resulting P-wave velocity-depth model confirms the typical volcanic margin structure. An underplated body is resolved as distinctive high seismic velocity (v_p up to 7.5 km/s) feature in the lower crust in the prolongation of a seaward dipping reflector sequence. A remarkable result is that a second, isolated body of high seismic velocity (v_p up to 7.3 km/s) exists landward of the first high-velocity feature. The centres of both bodies are 60 km apart. The high-velocity lower-crustal bodies likely were emplaced during transient magmatic–volcanic events accompanying the late rifting and initial drifting stages. The lateral variability of the lower crust may be an expression of a multiple rifting process in the sense that the South Atlantic rift evolved by instantaneous breakup of longer continental margin segments. These segments are confined by transfer zones that acted as rift propagation barriers. A lower-crustal reflector was detected at 3 to 5 km above the modern Moho and probably represents the lower boundary of stretched continental crust. With this finding we suggest that the continent–ocean boundary is situated 70 km more seaward than in previous interpretations.     

Effect of implementing ecosystem functional type data in a mesoscale climate model

In this paper, we introduce a new concept of land-surface state representation for southern South America, which is based on "functional" attributes of vegetation, and implement a new land-cover (Ecosystem Functional Type, hereafter EFT) dataset in the Weather and Research Forecasting (WRF) model. We found that the EFT data enabled us to deal with functional attributes of vegetation and time-variant features more easily than the default land-cover data in the WRF. In order to explore the usefulness of the EFT data in simulations of surface and atmospheric variables, numerical simulations of the WRF model, using both the US Geological Survey (USGS) and the EFT data, were conducted over the La Plata Basin in South America for the austral spring of 1998 and compared with observations. Results showed that the model simulations were sensitive to the lower boundary conditions and that the use of the EFT data improved the climate simulation of 2-m temperature and precipitation, implying the need for this type of information to be included in numerical climate models.     

Evaluating the design of an earth dam by finite element analysis

An earth dam was to be constructed on a site which posed non-uniform foundation conditions. The most prominent feature was a vertical contact between unweathered quartzite and decomposed diabase running parallel to the valley. The paper describes a two-dimensional finite element analysis on the foundation and embankment to determine relative settlements and the possibility of hydraulic fracturing of the clay core. The analysis was extended to evaluate the effectiveness of site improvement measures such as excavation and recompaction of the decomposed diabase and elimination of the contact problem by blasting into the unweathered quartzite. Comparing results from the various analyses, it was concluded that the latter was the only viable solution to the problem.     

Changes in solar irradiance and atmospheric turbidity in Costa Rica during the total solar eclipse of July 11, 1991

Solar global radiation was measured in several places in Costa Rica during the total solar eclipse that occurred on July 11, 1991. In two of these places, Puntarenas and Santa Cruz, measurements in the ultraviolet range (295–385 nm) were also taken. In Santa Cruz, a normal incidence pyrheliometer with Schott filters OG530 and RG630 was used to measure direct solar radiation in its whole range, and in the 530–2800 nm and 630–2800 wavebands respectively. Global radiation, and consequently direct, diffuse and irradiance in any of the wavebands considered, decreased gradually as the sun was being eclipsed and reached zero during the totality, then increased to their normal values. Data registered in Santa Cruz were used to determine Ångstrom's atmospheric turbidity parameters and. Computations show that between 13:00 and 14:30 LT (local time), decreased and increased significantly. This indicates that atmospheric turbidity was high and large particles were more abundant than small ones. The size of hygroscopic particles increased during the eclipse when temperature decreased and relative humidity increased in a comparatively short time.     

1-, 2-, and 3-dimensional effective conductivity of aquifers

Starting with a stochastic differential equation with random coefficients describing steady-state flow, the effective hydraulic conductivity of 1-, 2-, and 3-dimensional aquifers is derived. The natural logarithm of hydraulic conductivity (lnK) is assumed to be heterogeneous, with a spatial trend, and isotropic. The effective conductivity relates the mean specific discharge in an aquifer to the mean hydraulic gradient, thus its importance in predicting Darcian discharge when field data represent mean or average values of conductivity or hydraulic head. Effective conductivity results are presented in exact form in terms of elementary functions after the introduction of special sets of coordinate transformations in two and three dimensions. It was determined that in one, two, and three dimensions, for the type of aquifer heterogeneity considered, the effective hydraulic conductivity depends on: (i) the angle between the gradient of the trend of lnK and the mean hydraulic gradient (which is zero in the one-dimensional situation); (2) (inversely) on the product of the magnitude of the trend gradient of lnK, b, and the correlation scale of lnK, and (3) (proportionally) on the variance of lnK, _f ² . The productb plays a central role in the stability of the results for effective hydraulic conductivity.     

An event-by-event assessment of tropical intraseasonal perturbations for general circulation models

We detect and characterize each large-scale intraseasonal perturbation in observations (1979–2009) and in coupled general circulation models of Institut Pierre Simon Laplace (IPSL) and of Centre National de Recherches Météorologiques (CNRM). These ensembles of intraseasonal perturbations are used to assess the skill of the two models in an event-by-event approach. This assessment addresses: (1) the planetary-scale (i.e. the whole Indo-Pacific area) extent of wind and rainfall perturbations and the reproducibility of the perturbation patterns for a given season; (2) the size and amplitude of rainfall and wind anomalies at basin-scale (i.e. for a particular phase of the perturbation) and; (3) the evolution of the vertical structure of the perturbations (U, T and RH) for selected events. The planetary-scale extent of rainfall perturbations is generally too small for both models. This extent is also small for the wind perturbation in the IPSL model, but is correct, or even too large in boreal winter, for the CNRM model. The reproducibility of the planetary-scale patterns is exaggerated for wind perturbations in the CNRM model and is very poor for all parameters in the IPSL model. Over the Indian Ocean during boreal winter, rainfall and wind anomalies at basin-scale are too large for the CNRM model and too small for the IPSL model. The CNRM model gives a realistic baroclinic perturbations structure for wind, moisture and temperature, but with too large amplitude due in part to a zonally extended rainfall anomaly over the eastern Indian Ocean and the Maritime Continent. The IPSL model gives a realistic response for low-level wind only. Temperature and moisture perturbations are barotropic with a wrong warm anomaly at rainfall maximum and there is no gradual increase in low-level moisture prior to this rainfall maximum. These results suggest that this version of the IPSL model is unable to initiate the coupling between the convection and the dynamic necessary to develop the perturbation. It is difficult to say if this is due to, or is at the origin of the lack of basin-scale organization of the convection. We discuss the likely role of the convective schemes in the differences found between these two versions of the CNRM and IPSL models.     

Surface water quality in a sulfide mineral‐rich arid zone in North‐Central Chile: Learning from a complex past,addressing an uncertain future

This study presents an analysis of up to 30 years of hydrological variables and selected water quality parameters (pH, SO₄, Fe, Cu, and As) in the upper area of the Elqui River basin in North‐Central Chile. A correlation analysis determined statistically significant positive relationship for SO₄‐Cu, Fe‐As, and Fe‐Cu. In terms of historical behaviour, no statistically significant trends were detected for precipitation or temperature. In contrast, for flow, there is an overall decreasing pattern for the entire area of study, although only in one case this trend was statistically significant. Along with the aforementioned analysis, a characterization of the flow‐water quality relationships is considered for the time period analyzed. Although erratic behaviours were confirmed, a negative (i.e., inverse) flow‐concentration relationship was identified for SO₄, a positive (i.e., direct) relationship for Fe, and undefined relationships for As and Cu were obtained. From these analyses and based on previous studies on projections regarding climate change for the Andean region, and in particular for the upper Elqui zone, an estimation of the possible effects of the change in water regimes on water quality in the area of study is developed. It is likely that a decrease in surface flow, as a consequence of climate change could translate into improvements in water quality in terms of Fe and eventually As and Cu, but into an impairment in the case of SO₄. In any case, this is a complex situation that demands special attention in the face of industrial activities that could be developed in tributaries like the Claro River, which currently play an important role in depurating or diluting contaminants in the waters of the Elqui River. Finally, it should be noted that this study addresses an issue that goes beyond the local interest and could be used as a reference to compare other transitional environments containing sulphide ores or areas of hydrothermal alterations, which are considered to be highly vulnerable to climate change and variability.