“Proterozoic–Early Paleozoic evolution in western South America—a discussion” in: Tectonophysics, 354: 121–137 (2002)     

Ricardo A. Astini  Augusto E. Rapalini   《Tectonophysics》2003,366(1-2):143-148

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Geochemical and stable isotopic evolution of the Guarani Aquifer System in the state of São Paulo, Brazil     

Ondra Sracek  Ricardo Hirata 《Hydrogeology Journal》2002,10(6):643-655

The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer System (Botucatu and Piramboia aquifers) in S?o Paulo State, Brazil. Trends of dissolved species concentrations and geochemical modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na–HCO₃ type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of groundwater flow and at present is located near to the cities of Sert?ozinho and águas de Santa Barbara (wells PZ-34 and PZ-148, respectively) in a shallow confined area, 50–70 km from the recharge zone. Part of the sodium probably enters the Guarani Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ ²H and δ ¹⁸O values in groundwater downgradient. Values of δ ¹³C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ ¹³C(DIC) in deep geothermal wells are very high (>–6.0‰) and probably indicate isotopic exchange with carbonates with δ ¹³C about –3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination to the Guarani Aquifer System. Electronic Publication  相似文献   

Vulnerability of water resources,vegetation productivity and soil erosion to climate change in Mediterranean watersheds     

João Pedro Nunes  Júlia Seixas  Nuno Ricardo Pacheco 《水文研究》2008,22(16):3115-3134

Climate change is expected to increase temperatures and lower rainfall in Mediterranean regions; however, there is a great degree of uncertainty as to the amount of change. This limits the prediction capacity of models to quantify impacts on water resources, vegetation productivity and erosion. This work circumvents this problem by analysing the sensitivity of these variables to varying degrees of temperature change (increased by up to 6·4 °C), rainfall (reduced by up to 40%) and atmospheric CO₂ concentrations (increased by up to 100%). The SWAT watershed model was applied to 18 large watersheds in two contrasting regions of Portugal, one humid and one semi‐arid; incremental changes to climate variables were simulated using a stochastic weather generator. The main results indicate that water runoff, particularly subsurface runoff, is highly sensitive to these climate change trends (down by 80%). The biomass growth of most species showed a declining trend (wheat down by 40%), due to the negative impacts of increasing temperatures, dampened by higher CO₂ concentrations. Mediterranean species, however, showed a positive response to milder degrees of climate change. Changes to erosion depended on the interactions between the decline in surface runoff (driving erosion rates downward) and biomass growth (driving erosion rates upward). For the milder rainfall changes, soil erosion showed a significant increasing trend in wheat fields (up to 150% in the humid watersheds), well above the recovery capacity of the soil. Overall, the results indicate a shift of the humid watersheds to acquire semi‐arid characteristics, such as more irregular river flows and increasingly marginal conditions for agricultural production. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Declustering of Clustered Preferential Sampling for?Histogram and Semivariogram Inference   总被引：1，自引：0，他引：1  

Ricardo A. Olea 《Mathematical Geology》2007,39(5):453-467

Measurements of attributes obtained more as a consequence of business ventures than sampling design frequently result in samplings that are preferential both in location and value, typically in the form of clusters along the pay. Preferential sampling requires preprocessing for the purpose of properly inferring characteristics of the parent population, such as the cumulative distribution and the semivariogram. Consideration of the distance to the nearest neighbor allows preparation of resampled sets that produce comparable results to those from previously proposed methods. A clustered sampling of size 140, taken from an exhaustive sampling, is employed to illustrate this approach.  相似文献   

Declustering of Clustered Preferential Sampling for Histogram and Semivariogram Inference     

Ricardo A. Olea 《Mathematical Geosciences》2007,39(5):453-467

Measurements of attributes obtained more as a consequence of business ventures than sampling design frequently result in samplings that are preferential both in location and value, typically in the form of clusters along the pay. Preferential sampling requires preprocessing for the purpose of properly inferring characteristics of the parent population, such as the cumulative distribution and the semivariogram. Consideration of the distance to the nearest neighbor allows preparation of resampled sets that produce comparable results to those from previously proposed methods. A clustered sampling of size 140, taken from an exhaustive sampling, is employed to illustrate this approach.  相似文献   

Turbulent carbon exchange in very stable conditions     

Otávio C. Acevedo  Osvaldo L. L. Moraes  David R. Fitzjarrald  Ricardo K. Sakai  Larry Mahrt 《Boundary-Layer Meteorology》2007,125(1):49-61

Turbulent fluxes obtained using the conventional eddy covariance approach result in erratic results with large time fluctuations in extremely stable conditions. This can limit efforts to estimate components of the nocturnal energy budget and respiratory CO₂ fluxes. Well-organized fluxes that show a clear dependence on turbulent intensity were obtained when multiresolution decomposition was used to estimate turbulent exchanges. CO₂, heat and water vapour fluxes were observed at a site in the eastern Amazon basin that had been cleared for agricultural purposes. Temporal scales of the carbon transfer were determined and shown to be similar to those of latent heat, but as much as three times larger than those of sensible heat. CO₂ eddy diffusivities at the temporal scales on which most of the vertical CO₂ exchange occurs are shown to be 50 times larger than the eddy diffusivity for heat. A process associated with the vertical scale of the scalar accumulation layer is suggested to explain these different scales and turbulent diffusivities of carbon and sensible heat transfer. For an appreciable range of turbulence intensities, the observed vertical turbulent carbon exchange is insufficient to account for the locally respired CO₂ estimated independently. Evidence that shallow drainage currents may account for this is given.  相似文献   

The Influence of the North Atlantic Oscillation on Rainfall Triggering of Landslides near Lisbon   总被引：1，自引：0，他引：1  

Ricardo?M.?TrigoEmail author  José L.?Zêzere  Maria?L.?Rodrigues  Isabel?F.?Trigo 《Natural Hazards》2005,36(3):331-354

The majority of landsliding episodes in the area north of Lisbon are associated with rainfall events of short (less than 5 days) medium (5–20 days) or long duration (more than 20 days). The precipitation regime in Portugal is highly irregular, with large differences between wet and dry years. We have assessed the impact of the North Atlantic Oscillation (NAO) on both the winter precipitation and the timing and magnitude of associated landslide events. Results show that the large inter-annual variability of winter precipitation is largely modulated by the NAO mode. The precipitation composite corresponding to high NAO index presents a considerable lower median value (47 mm/month) than the corresponding low NAO index class (134 mm/month). The entire precipitation distribution associated with the low NAO index composite encompasses a wider range of values than the corresponding high NAO index composite. This non-linear behavior is reflected in the probability of occurrence of a very wet month (precipitation above the 90% percentile) that is just 1% for the positive NAO class and 23% for low NAO index months. Results for the low NAO class are crucial because these months are more likely associated with long-lasting rainfall episodes responsible for large landslide events. This is confirmed by the application of a 3-month moving average to both NAO index and precipitation time series. This procedure allowed the identification of many months with landslide activity as being characterized by negative average values of the NAO index and high values of average precipitation (above 100 mm/month). Finally, using daily data we have computed the return periods associated with the entire set of landslide episodes and, based on these results, obtained a strong linear relationship between critical cumulative rainfall and the corresponding critical rainfall event duration.  相似文献   

Estimating the mean temperature and salinity of the Chesapeake Bay mouth     

Ricardo?A.?Locarnini  Larry?P.?AtkinsonEmail author  Arnoldo?Valle-Levinson 《Estuaries and Coasts》2002,25(1):1-5

We used an extensive temperature and salinity data set to develop a statistically meaningful way of estimating mean temperature and salinity from discrete measurements in the mouth of Chesapeake Bay. From April 1992 to December 1998, the Center for Coastal Physical Oceanography completed 73 monthly hydrographic sections at high spring tide across the mouth of Chesapeake Bay. Time series of area weighted mean bay mouth temperature (MBMT) and salinity (MBMS) were calculated. We found that at any time the temperature at any location in the section correlated with the MBMT with a r² of 0.95 or better. A similar analysis for salinity showed that the best correlation was about 0.9 with many locations below 0.8. A correlation between MBMT and temperature at a nearby tide station indicated it was possible to estimate MBMT from the temperature at the tide station to ±0.74°C (90% confidence interval). Salinity was not measured at the tide station, but the correlation at a location in the section similar to the tide station indicates that MBMS can be estimated with an error of ±1.5 (90% confidence interval).  相似文献   

The spring bloom in the Antarctic Polar Frontal Zone as observed from a mesoscale array of bio-optical sensors     

Mark R. Abbott  James G. Richman  Ricardo M. Letelier  Jasmine S. Bartlett 《Deep Sea Research Part II: Topical Studies in Oceanography》2000,47(15-16)

The US Joint Global Ocean Flux Study (JGOFS) conducted a series of survey and process studies in part to understand the processes regulating primary productivity and carbon flux in the APFZ, which is a high-nutrient, low-chlorophyll (HNLC) region. We deployed a high-resolution array of 12 moorings (average horizontal spacing 30 km) equipped with bio-optical and physical sensors to study the temporal and spatial scales of biological and physical processes in the APFZ. The moorings collected data from November 1997 to March 1998, effectively observing the growing season. Estimates of chlorophyll and sun-stimulated fluorescence/chlorophyll (F/C) were derived from the bio-optical measurements. Each mooring showed a strong spring bloom beginning in early December as the upper ocean began to stratify, with chlorophyll levels nearly quadrupling. The time series, along with ship studies, suggest that phytoplankton were initially light-limited as a result of deep, late spring mixing, followed by intense zooplankton grazing or silicate limitation, which controlled the maximum chlorophyll concentration, and finally by iron limitation, which led to increasing photoadaptive stress. These results suggest that phytoplankton in the APFZ are regulated by a confluence of processes involving light, grazing, silicate, and iron, and that models comprising a single mechanism may not be sufficient. The spring bloom in the APFZ is a transient event, persisting for only a few weeks, and therefore it is difficult to draw conclusions from sporadic ship cruises. Moreover, its spatial scales are also small so that widely spaced hydrographic stations can easily overlook critical processes.  相似文献   

Characterizing rainfall‐runoff signatures from micro‐catchments with contrasting land cover characteristics in southern Amazonia          下载免费PDF全文

Alphonce C. Guzha  Rodolfo L. B. Nobrega  Kristof Kovacs  Jessica Rebola‐Lichtenberg  Ricardo S. S. Amorim  Gerhard Gerold 《水文研究》2015,29(4):508-521

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