Basins Of South America Research Articles

Facies analysis and depositional environments of Permian carbonates of the Venezuelan Andes: Palaeogeographic implications for Northern Gondwana

Upper Palaeozoic strata in South America were deposited over cratonic areas and in intracratonic basins (e.g. Solimões, Amazonas, Paraná); however in many areas such as Venezuela and Colombia they are rarely exposed through dense vegetation and the nature of the terrain, so that the strata are poorly documented. However, these strata do have significant implications for the palaeogeography of the time. This article reports on a study of the Permian carbonates of the Palmarito Formation, exposed throughout the Venezuelan Andes, and discusses the succession of palaeoenvironments and the palaeogeography resulting from detailed field and lab work. Deposition took place on an extensive ramp which probably dipped gently northwards towards the open ocean. Much of the Palmarito succession shows a general transgressive trend, with a few thinner, more-regressive intervals, likely a response to glaciation–deglaciation cycles. Towards the end of the Permian in the Venezuelan Andes region, a major sea-level fall led to extensive uplift and erosion, resulting in a major disconformity between the Upper Guadalupian carbonates and overlying Jurassic red beds. The early Palmarito tidal-flat facies are noteworthy for their sub-metre-scale mud-to-sand cycles with incipient palaeosoil fabrics. Overlying mid-outer ramp carbonate facies are characterised by thin storm beds and bioclastic lenses, arranged into metre-scale coarsening-upward cycles. Succeeding shallow-marine inner-mid ramp, bioclastic grain–wacke-stones are dominated by an open-marine fauna of fusulinids, calcareous algae, crinoids, bryozoans and brachiopods. Outer-ramp facies are wacke–mud-stones with sponge spicules, radiolarians and brachiopod fragments. There are similarities between the Permian deposits of Venezuela and those recorded from Guatemala and México to the north, and from Colombia and Perú–Bolivia to the west and southwest, where carbonate systems also dominate. These facies were all part of a tropical foreland basin setting, the Mucuchachi Basin, which contrasts with the other Late Palaeozoic intracratonic basins in South America. Evidence provided here demonstrates that a seaway existed between Laurentia and Gondwana from the Early Permian through to the late Early Permian.

Land Cover Change Effects on the Climate of the La Plata Basin

AbstractDeforestation and replacement of natural pastures by agriculture have become a common practice in the La Plata River basin in South America. The changes in land cover imply changes in the biophysical properties of the land surface, with possible impacts on the basin’s hydroclimate. To help understand to what extent the climate could be affected, and through which processes, ensembles of seasonal simulations were prepared using the Weather Research and Forecasting Model for a control case and a scenario assuming an expansion of the agricultural activities to cover the entire basin. The La Plata River basin shows different climate responses to the land cover changes depending on the region. The northern part of the basin, where forests and savanna were replaced by crops, experiences an overall increase in albedo that leads to a reduction of sensible heat flux and near-surface temperature. A reduction of surface roughness length leads to stronger low-level winds that, in turn, favor a larger amount of moisture being advected out of the northern part of the basin. The result is a reduction of the vertically integrated moisture flux convergence (VIMFC) and, consequently, in precipitation. In the southern part of the basin, changes from grasslands to crops reduce the albedo and thus increase the near-surface temperature. The reduction in surface roughness length is not as large as in the northern sector, reducing the northerly moisture fluxes and resulting in a net increase of VIMFC and, thus, in precipitation. Notably, advective processes modify the downstream circulation and precipitation patterns over the South Atlantic Ocean.

Population divergence and peculiar karyoevolutionary trends in the loricariid fish Hypostomus aff. unae from northeastern Brazil

Loricariidae (Siluriformes, Hypostominae) is one of the most diverse catfish families. In spite of the wide distribution of loricariids in South America, cytogenetic reports are available for only a few species, mostly from southern and southeastern Brazil. We made the first chromosomal analysis of Hypostomus aff. unae from the Contas River basin in northeastern Brazil. Four populations isolated by short distances but from distinct landscapes were studied based on conventional staining, C-banding, argyrophilic nucleolar organizer regions (Ag-NOR), CMA(3)/DAPI fluorochrome staining, and fluorescent in situ hybridization with 18S rDNA probes. Although sharing the same diploid number (2n = 76) and NOR locations, each population presented exclusive karyotype formulae and specific patterns of heterochromatic and AT-rich regions. The derived karyotypes of H. aff. unae (2n >54; high number of acrocentrics bearing AT-rich interstitial heterochromatin) indicated a divergent karyoevolution, mostly driven by centric fissions, pericentric inversions and particular heterochromatin dispersion models. This finding of distinct evolutionary units in H. aff. unae will be useful for understanding the natural history of loricariids from relatively unexplored coastal basins in South America.

Hepatitis D infection in Nigeria

Hepatitis D virus (HDV) is a defective RNA virus that requires the hepatitis B envelope for its replication. Infection with HDVoccurs as co-infection or superinfection in persons infected with hepatitis B virus (HBV). Chronic HDVinfection usually follows superinfection of chronic HBV infection with HDV. Unlike some other infections, persistent HDV infection is associated with presence of HDV RNA, viral antigen (HDAg), and IgM and IgG antibodies to HDV [1]. HDV has a worldwide distribution with nearly 15 million people infected, especially in the Mediterranean Basin, the Middle East, Central Asia, West Africa, the Amazon Basin of South America and certain South Pacific islands [2]. In Nigeria, HBV infection is a major cause of liver disease [3]. In a previous report, HDVantigen was detected in 6.5% of patients with chronic HBV liver disease in Ife, South West Nigeria [4]. With measures for preventing HBV infection (including vaccination and safe blood transfusion), HDV infection may be on the decline [5]. However recent reports, including one from our locality, have tended to indicate otherwise [6, 7]. We set out to investigate the current status of HDV infection. After ethical approval, consecutive consenting patients attending the Gastroenterology Unit of Lagos State University Hospital, Lagos between September 2009 to November 2010 were recruited if they were positive for HBsAg for more than 6 months and had not received any antiviral therapy. A questionnaire was used to collect information on demographics, clinical features, liver biochemical tests and imaging results. Blood (10 mL) was collected in EDTA, and plasma was separated and stored at −20 C. IgG anti-HDV antibodies were assayed using an Elisa method (HDVAb kit; DIA PRO Diagnostic, Milan, Italy) according to the manufacturer’s protocol. The sensitivity and specificity of this assay kit are over 98%. A total of 245 patients (191 male) with age range 13–76 (mean [SD]034.6 [10.6]) years were studied. Of these, 178 were asymptomatic HBV carriers, whereas 67 had features of chronic liver disease (chronic hepatitis 22, cirrhosis 37 and liver cancer 8). Five (2.0%; 2 male) of these 245 patients tested positive to anti-HDV. These included 3 of 178 asymptomatic carriers and 2 of 67 patients with liver disease. Alanine aminotransferase (ALT) levels were mildly elevated in two anti-HDV positive persons and were normal in three. Our study patients with chronic HBV infection had a lower prevalence of anti-HDV antibody as compared to previous reports [4, 7] from our locality with prevalence rates of 6.5% for HDAg and 12.5% for HDV antibody, respectively. Possible explanations for this difference may relate to the characteristics of the study subjects, the assay or an actual reduction in disease burden. Among the previous studies, one by Ojo et al. [4] had smaller sample size, consisted of patients symptomatic for liver disease and the assay was for HDV antigen. The other study [7] included both symptomatic and asymptomatic persons, but had a larger sample size. Our study, as well as both the previous studies, were limited by the fact that testing for HDV RNA, a better marker of HDV infection, was not done. A true reduction in HDV prevalence rates over time is also possible; this could have resulted from measures to prevent HBV infection embarked during the last two decades. A recent study showing HBsAg prevalence of about 8% Part of this work was presented as a poster during the EASL Monothematic Conference in Istanbul, Turkey in September 2010. C. A. Onyekwere (*) : F. Duro-Emmanuel Department of Medicine, Lagos State University Teaching Hospital, Lagos, Nigeria e-mail: ifymobi@yahoo.com

The Silala/Siloli Watershed: Dispute over the Most Vulnerable Basin in South America

The dispute over the Silala (or Siloli) Basin, shared by Bolivia and Chile, illustrates the importance of history, the role of indigenous communities, and the effects of differences in national socio-economic philosophies informing water resource management in international negotiations concerning transboundary watercourses, regardless of their size. The Silala case provides an illuminating example of the overlap between surface and groundwater regimes, and the range of interpretations states can uphold regarding this complex interaction. The objective of this paper is to present a brief case study, including a physical description, historical review, summary of current status, and discussion of the legal context of the transboundary Silala Basin.

Population structure of the migratory fish Prochilodus lineatus (Characiformes) from rio Grande basin (Brazil), an area fragmented by dams

Abstract Prochilodus lineatus (Prochilodontidae, Characiformes) is a migratory species of great economic importance both in fisheries and aquaculture that is found throughout the Jacuí, Paraíba do Sul, Paraná, Paraguay and Uruguay river basins in South America. Earlier population studies of P. lineatus in the rio Grande basin (Paraná basin) indicated the existence of a single population; however, the range of this species has been fragmented by the construction of several dams. Such dams modified the environmental conditions and could have constrained the reproductive migration of P. lineatus, possibly leading to changes in the population genetic structure. In order to evaluate how genetic diversity is allocated in the rio Grande basin, 141 specimens of P. lineatus from eight collection sites were analysed using polymerase chain reaction–restriction fragment length polymorphism (PCR‐RFLP) with 15 restriction enzymes. Forty‐six haplotypes were detected, and 70% of them are restricted. The mean genetic variability indexes (h = 0.7721 and π = 1.6%) were similar to those found in natural populations with a large effective size. Fst and Exact Test values indicated a lack of structuring among the samples, and the model of isolation by distance was tested and rejected. The haplotype network indicated that this population of P. lineatus has been maintained as a single variable stock with some differences in the genetic composition (haplotypes) between samples. Indications of population expansion were detected, and this finding was supported by neutrality tests and mismatch distribution analyses. The present study focused on regions between dams to serve as a parameter for further evaluations of genetic variability and the putative impact of dams and repopulation programmes in natural populations of P. lineatus. Copyright © 2011 John Wiley & Sons, Ltd.

Development of a benthic multimetric index for biomonitoring of a neotropical watershed

Biotic indices are important tools for evaluating water quality in Biomonitoring Programmes of river basins. The objective of this study was to develop a Benthic Multimetric Index (BMI) to evaluate the water quality in a neotropical catchment in southeastern Brazil. Thirty metrics were evaluated and six were selected to calculate the BMI: family richness, % Oligochaeta, % Chironomidae + Oligochaeta (% CHOL), % EPT (Ephemeroptera, Plecoptera and Trichoptera), % Collector-gatherers, and BMWP-CETEC biotic index. Sampling was carried in triplicate at 21 sampling sites (8 in the river channel and 13 in the tributaries) during 4 annual collecting trips from June 2004 to November 2007, making a total of 945 samples. Scores (5, 3 or 1) were attributed to each chosen metric and were added up to establish the water quality criteria (a score of 6-12 - poor; 13-18 - intermediate; 19-24 - good; and 25-30 - very good water quality). Our results indicated that 48% of the sampling sites analysed in the catchment basin presented very good water quality, 14% good quality, 19% regular, and 19% poor water quality. This methodology proved to be an efficient tool for evaluating water quality in the Biomonitoring Programme of the Velhas River basin, and that it may serve to evaluate water quality in other river basins in South America.

Chromosomal Characterization of Prochilodus lineatus from Parana River, Corrientes, Argentina. I. B Chromosomes and NOR Banding

The fish of the genus Prochilodus, commonly known as sabalo, are of great economic and ecological importance. Different species of this genus are widely distributed throughout all the basins of South America. Cytogenetic analysis performed on specimens of Prochilodus lineatus from Puerto Abras (Parana River, Argentina), revealed the occurrence of 54 chromosomes of meta-submetacentric type, together with the presence of small supernumerary chromosomes with intra and interindividual variations. The use of the 18S rDNA probe confirmed the results obtained with Ag-NORs, identifying the presence of a metacentric chromosome pair with ribosomal cistrons in interstitial position in the long arm. Through both of these techniques are noted differences in the size of the nucleolar regions, this variation is probably related to the occurrence of events of duplication and/or deletion.

Unsuitability of Cnesterodon decemmaculatus (Jenyns, 1842) for mosquito control in Uruguay: evidence from food-preference experiments

We analyzed the feeding preference of Cnesterodon decemmaculatus, a small-bodied poecilid native from the Rio de la Plata and proximate Atlantic Basins in South America. This species has a wide distribution in Uruguayan water bodies but its effectiveness as a predator of mosquito larvae has not been tested. In laboratory trials, five aquatic invertebrates were offered simultaneously as potential prey to fish: Daphnia pulex (Cladocera), copepods, two different instars of mosquito larvae (Culex pipiens), and the 4th instar of Chironomidae larvae. Preference was measured by the Chesson's electivity index (α). In order to determine differences in prey preference according to fish size, individuals ranging from 9.5 mm to 35.3 mm were classified in three different body size classes: small, medium, and large. Small fish showed preference for copepods, while medium-sized fish preferred the smallest mosquito larvae instars and Chironomidae larvae. We conclude that C. decemmaculatus is a zooplankton facultative-feeder fish that prefers large-bodied zooplankton but is a weak predator of mosquito larvae. Thus, the introduction of C. decemmaculatus as a biological-control agent in natural environments is not an effective strategy.

Comparing surface energy, water and carbon cycle in dry and wet regions simulated by a land-surface model

In this study, we analyze results from 47-year (1954–2000) offline simulations using an Australian land-surface model CSIRO Atmosphere Biosphere Land Exchange. We focus on exploring its surface mean climatology, interannual and decadal variations in Australia and Amazonia basin in South America which are distinguished by dry and wet climates respectively. Its skill is assessed by using observational datasets and four model products from the Global Land-surface Data Assimilation System. Surface evaporation and runoff climatologies are satisfactorily simulated, including surface energy and water partitions in dry and wet climates. In the Australian continent dominated by dry climate, slowly varying soil moisture processes are simulated in the southeast during austral winter. The model is skilful in reproducing the nonlinear relationship between rainfall and runoff variations in the southwestern part of the Australia. It shows that the significant downward trend of river inflow in the region is associated with enhanced surface evaporation which is caused by increased surface radiation and wind speed. In its carbon-cycle modeling, the model simulates an upward trend of NPP by about 0.69%/year over the Amazonia forest region in the 47-year period. By comparing two sets of the model results with/without CO2 variations, it shows that 35% of such increases are caused by changes in climatic conditions, while 65% is due to the increase in atmospheric CO2 concentration. Given the close linkage between climate, water and vegetation (carbon cycle), this work promotes an integrated modeling and evaluation approach for better representation of land-surface processes in Earth system studies.

Application of GIS and remote sensing techniques in generation of land use scenarios for hydrological modeling

Changes in land use and the relationship between land use changes and different explanatory variables were studied. Future scenarios of land use were developed using logistic regression (Reg-Log) and Neural Networks (MPL) for a horizon year 2001, applying in both cases a process of multiobjective allocation of land uses (MOLA). Validated the results, we generated a scenario of land occupation to 2012. ► The persistence of the different land occupations is the predominant state in the study area. The changes are produced in the boundary area among categories. ► The greater explanatory power of the occurrence of the different coverage was presented by biophysical variables. ► The best estimate of the land use change was produced when applying logistic regression. ► The most difficult land use to predict was of crops. ► The scenery generated for 2012 showed a remarkable similarity with the map of land use corresponding to 2001; this is due to little dynamism of the explanatory variables. This research studies the change in land use in a binational hydrographic basin in South America. In addition, a future perspective for land use is generated according to the trends in the development observed. A multi-temporal analysis of land use change is carried out and variables that can explain the observed transitions will be selected. The relations between changes and explicative variables are studied in order to stochastically model future land use maps. Persistence was found to be the predominant state. Higher transitions were observed in the zones of boundaries between categories. Biophysical variables had the most explicative power with a better performance of the model based on logistic regression than the one made by using neural networks.

Poverty, governance and conservation in the Gran Chaco of South America

The Gran Chaco is the second largest ecosystem in the Plata basin of South America, after the Amazon rainforest. The high biological and cultural diversity offer diverse opportunities for conservation, despite development threatening both of them. The greatest concentration of biodiversity remain in areas of northern Argentina and southern Bolivia where levels of poverty are very high, and indigenous peoples and poor criollo cattle raisers coexist. By improving informed governance, it is possible to stabilize biodiversity levels and provide a basis for poor local people to collaborate, and to improve their situation in the face of threats from development. In this study we analyze the ongoing processes being applied in two Gran Chaco cases—from the Upper Parapeti Basin (upriver from Kaa Iya National Park) in Bolivia, and the Lower Pilcomayo in northern Argentina (a dynamic internal delta ecosystem where a tri-national biosphere reserve is being considered). Watershed management, when adapted to local ecological, cultural, social and political contexts, is shown to be an effective tactical strategy to activate moribund governmental institutions in response to local constituencies. In the two cases presented, NGO-facilitated processes enriched local people's ability to take their own actions and to assess and frame their problems and goals for dialogue with their governments. The NGOs also offered technical assistance with land-use zoning, reforestation and alternative income-generation activities in collaborations that shifted government engagement. The methods used differ from the standard conservation and development projects, and their success offers lessons in building social network systems and civic science that improve conservation and reduce poverty. We close with a reflection on the framing of poverty alleviation and sustainability in conservation discourse.

30 million years of Permian volcanism recorded in the Choiyoi igneous province (W Argentina) and their source for younger ash fall deposits in the Paraná Basin: SHRIMP U–Pb zircon geochronology evidence

We present four SHRIMP U–Pb zircon ages for the Choiyoi igneous province from the San Rafael Block, central–western Argentina. Dated samples come from the Yacimiento Los Reyunos Formation (281.4 ± 2.5 Ma) of the Cochicó Group (Lower Choiyoi section: andesitic breccias, dacitic to rhyolitic ignimbrites and continental conglomerates), Agua de los Burros Formation (264.8 ± 2.3 Ma and 264.5 ± 3.0 Ma) and Cerro Carrizalito Formation (251.9 ± 2.7 Ma Upper Choiyoi section: rhyolitic ignimbrites and pyroclastic flows) spanning the entire Permian succession of the Choiyoi igneous province. A single zircon from the El Imperial Formation, that is overlain unconformably by the Choiyoi succession, yielded an early Permian age (297.2 ± 5.3 Ma), while the main detrital zircon population indicated an Ordovician age (453.7 ± 8.1 Ma). The new data establishes a more precise Permian age (Artinskian–Lopingian) for the section studied spanning 30 Ma of volcanic activity. Volcanological observations for the Choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes, capable of injecting enormous volumes of tephra in the troposphere–stratosphere. The new SHRIMP ages indicate contemporaneity between the Choyoi succession and the upper part of the Paraná Basin late Paleozoic section, from the Irati up to the Rio do Rasto formations, encompassing about 24 Ma. Geochemical data show a general congruence in compositional and tectonic settings between the volcanics and Paraná Basin Permian ash fall derived layers of bentonites. Thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions. Thus, we consider that the Choiyoi igneous province was the source of ash fall deposits in the upper Permian section of the Paraná Basin. Data presented here allow a more consistent correlation between tectono-volcanic Permian events along the paleo-Pacific margin of southwestern Gondwana and the geological evolution of neighboring Paleozoic foreland basins in South America and Africa.

The Yucatan peninsula: biogeographical history 65 million years in the making

The fourth biennial meeting of the International Biogeography Society (IBS) in Merida, Yucatan in January 2009 represented a double opportunity for Mexican biologists. First, it fostered the integration of the large community of Mexican biogeographers with the activities of the IBS. Second, the meeting allowed us to welcome a large number of delegates from distant parts of the world who were able to visit what has been considered an obligate destination for nature lovers and cultural tourists alike: the Yucatan peninsula. As Edward O. Wilson pointed out, besides economic power every country has two additional and important types of wealth: cultural and natural. Cultural richness is a naturally embedded component of the Mexican way of life.

Statistical properties of aerosol-cloud-precipitation interactions in South America

Abstract. Given the complex interaction between aerosol, cloud, and atmospheric properties, it is difficult to extract their individual effects to observed rainfall amount. This research uses principle component analysis (PCA) that combines Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and cloud products, NCEP Reanalysis atmospheric products, and rainrate estimates from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) to assess if aerosols affect warm rain processes. Data collected during September 2006 over the Amazon basin in South America during the biomass-burning season are used. The goal of this research is to combine these observations into a smaller number of variables through PCA with each new variable having a unique physical interpretation. In particular, we are concerned with PC variables whose weightings include aerosol optical thickness (AOT), as these may be an indicator of aerosol indirect effects. If they are indeed occurring, then PC values that include AOT should change as a function of rainrate. To emphasize the advantage of PCA, changes in aerosol, cloud, and atmospheric observations are compared to rainrate. Comparing no-rain, rain, and heavy rain only (>5 mm h−1) samples, we find that cloud thicknesses, humidity, and upward motion are all greater during rain and heavy rain conditions. However, no statistically significant difference in AOT exists between each sample, indicating that atmospheric conditions are more important to rainfall than aerosol concentrations as expected. If aerosols are affecting warm process clouds, it would be expected that stratiform precipitation would decrease as a function increasing aerosol concentration through either Twomey and/or semi-direct effects. PCA extracts the latter signal in a variable labeled PC2, which explains 15% of the total variance and is second in importance the variable (PC1) containing the broad atmospheric conditions. PC2 contains weightings showing that AOT is inversely proportional to low-level humidity and cloud optical thickness. Increasing AOT is also positively correlated with increasing low-level instability due to aerosol absorption. The nature of these weightings is strongly suggestive that PC2 is an indicator of the semi-direct effect with larger values associated with lower rainfall rates. PC weightings consistent with the Twomey effect (an anti-correlation between AOT and cloud droplet effective radius) are only present in higher order PC variables that explain less than 1% of the total variance, and do not vary significantly as a function of rainrate. If the Twomey effect is occurring, it is highly non-linear and/or being overshadowed by other processes. Using the raw variables alone, these determinations could not be made; thus, we are able to show the advantage of using advanced statistical techniques such as PCA for analysis of aerosols impacts on precipitation in South America.

Interhemispheric Influence of the Atlantic Warm Pool on the Southeastern Pacific

Abstract The Atlantic warm pool (AWP) is a large body of warm water comprising the Gulf of Mexico, Caribbean Sea, and western tropical North Atlantic. The AWP can vary on seasonal, interannual, and multidecadal time scales. The maximum AWP size is in the boreal late summer and early fall, with the largest extent in the year being about 3 times the smallest one. The AWP alternates with the Amazon basin in South America as the seasonal heating source for circulations of the Hadley and Walker type in the Western Hemisphere. During the boreal summer/fall, a strong Hadley-type circulation is established, with ascending motion over the AWP and subsidence over the southeastern tropical Pacific. This is accompanied by equatorward flow in the lower troposphere over the southeastern tropical Pacific, as dynamically required by the Sverdrup vorticity balance. It is shown by analyses of observational data and NCAR community atmospheric model simulations that an anomalously large (small) AWP during the boreal summer/fall results in a strengthening (weakening) of the Hadley-type circulation with enhanced descent (ascent) over the southeastern tropical Pacific. It is further demonstrated—by using a simple two-level model linearized about a specified background mean state—that the interhemispheric connection between the AWP and the southeastern tropical Pacific depends on the configuration of the background mean zonal winds in the Southern Hemisphere.

Negotiations Over Water and Other Natural Resources in the La Plata River Basin: A Model for Other Transboundary Basins?

AbstractThe La Plata River Basin in South America, whose waters are shared by Argentina, Bolivia, Brazil, Paraguay and Uruguay, provides important lessons from the long history of negotiations over its shared water and other natural resources. In particular, innovative resource management practices developed over time have led to the relative harmony in which the riparian countries coexist. In this article, we analyze negotiation techniques within the La Plata River Basin by examining in detail the processes leading to the two seminal agreements – the 1969 Treaty of La Plata Basin and the 1979 Itaipú-Corpus Agreement. Based upon our analysis of the complex and often contradictory relationships between the riparian states, we evaluate the outcomes of both treaties from the standpoint of cooperation in the region and sustainable development. In doing so, we extend the relevance of the analysis to other basins with similar issues of regional management. The article extends the basin cooperation, through negotiation, to include trade agreements and development via project partnerships that draw in regional and global actors, including non-governmental organizations, environmental lobbies in foreign countries, and multinational development banks. The above actors are relevant for many parts of the world in today's era of globalization.

Regional four‐dimensional hydrological mass variations from GRACE, atmospheric flux convergence, and river gauge data

The spatiotemporal behavior of the Earth's gravity field is traditionally modeled as a series expansion in terms of spherical harmonics with a number of time‐dependent coefficients. In this contribution we study regional effects, namely, hydrological mass variations observed by the Gravity Recovery And Climate Experiment (GRACE) satellite mission since 2002. As compared to the global spherical harmonics, scaling and wavelet functions are quasi‐compactly supported, i.e., highly localizing with respect to space and time. Consequently, they establish a system of base functions well suited for regional modeling. We determine a spatiotemporal regional gravity model from GRACE using the spherical wavelet technique for the spatial part and a one‐dimensional B spline expansion for the temporal variations; that is, we end up with a four‐dimensional multiresolution representation (MRR) of the geopotential over selected regional areas and time intervals. For an exemplary area consisting of three large river basins in South America we compute mass variations expressed in terms of equivalent water heights. We demonstrate that a B spline expansion for modeling the temporal behavior is more appropriate than the classical Fourier series approach. In order to corroborate the results, our storage estimates are balanced with the net effect of river discharge from gauges (outflow) and the difference of precipitation and evaporation (inflow) from the convergence of vertically integrated water vapor fluxes. Furthermore, our results are compared with monthly mass grids from GRACE spherical harmonic solution data products. We conclude that the MRR means a robust tool to maximize the observational accuracy for GRACE, it considers the spatiotemporal resolution of the observations due to resolution‐dependent highest levels, and it is applicable elsewhere globally to model hydrological or other phenomena of mass change.

Community dynamics of anaerobic bacteria in deep petroleum reservoirs

The nature, activity and metabolism of microbes that inhabit the deep subsurface environment are a matter of ongoing debate. The analysis of oil samples from three different basins in South America, central Europe and the Middle East indicates the presence of intact phospholipids and suggests that indigenous bacteria inhabit petroleum reservoirs in sediment depths of up to 2,000 m. The nature, activity and metabolism of microbes that inhabit the deep subsurface environment are a matter of ongoing debate1,2,3,4,5,6,7. Primarily limited by temperature8, little is known about secondary factors that restrict or enhance microbial activity9,10 or about the extent of a habitable environment deep below the surface. In particular, the degraders of chemically inert organic substrates remain elusive9. Petroleum reservoirs can be regarded as natural bioreactors and are ideally suited for the study of microbial metabolism in the deep subsurface. Here we analyse series of oil samples that were biodegraded to different degrees. We find fatty acids after hydrolysis of purified crude oil fractions, indicating the presence of intact phospholipids and suggesting that indigenous bacteria inhabit petroleum reservoirs in sediment depths of up to 2,000 m. A major change in bacterial community structure occurs after the removal of n-alkanes, indicating that more than one consortium is responsible for petroleum degradation11. Our results suggest that further study of petroleum fluids will help understand bacterial metabolism and diversity in this habitat of the deep subsurface.

Evaluation of TRMM Multisatellite Precipitation Analysis (TMPA) and Its Utility in Hydrologic Prediction in the La Plata Basin

Abstract Satellite-based precipitation estimates with high spatial and temporal resolution and large areal coverage provide a potential alternative source of forcing data for hydrological models in regions where conventional in situ precipitation measurements are not readily available. The La Plata basin in South America provides a good example of a case where the use of satellite-derived precipitation could be beneficial. This study evaluates basinwide precipitation estimates from 9 yr (1998–2006) of Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis (TMPA; 3B42 V.6) through comparison with available gauged data and the Variable Infiltration Capacity (VIC) semidistributed hydrology model applied to the La Plata basin. In general, the TMPA estimates agreed well with the gridded gauge data at monthly time scales, most likely because of the monthly adjustment to gauges performed in TMPA. The agreement between TMPA and gauge precipitation estimates was reduced at daily time scales, particularly for high rain rates. The TMPA-driven hydrologic model simulations were able to capture the daily flooding events and to represent low flows, although peak flows tended to be biased upward. There was a good agreement between TMPA-driven simulated flows in terms of their reproduction of seasonal and interannual streamflow variability. This analysis shows that TMPA has potential for hydrologic forecasting in data-sparse regions.