Carbon stable isotopes ratios of pelagic and littoral communities in Alchichica crater-lake, Mexico

Carbon stable isotope ratios were determined in dominant biotic components of pelagic and littoral systems in Alchichica crater-lake. Results showed that carbon signatures were significantly different between both systems. The pelagic environment was more depleted (−26.15 to −15.14 per mille) than the littoral zone (−21.03 to −17.91 per mille). The potential source end-point in the simplified pelagic community was established to be diatomaceous phytoplankton; its predicted value was −21.7 per mille. There is a clear evidence thatNodularia does not sustain the pelagic food chain. In contrast, the highly diverse littoral community was sustained by epiphytes. No allochthonous sources seemed to influence this food web.¹³C enrichment was observed along the components of both systems with fractionations of 0.8 to 1.4 per mille. The contribution of the seagrassRuppia maritima is probably associated with the detritus pathway. Carbon source partitioning between both systems was not recorded. The δ¹³C in Alchichica crater-lake was more enriched than in other saline lakes and could be attributed to different salinity and CO₂ concentrations among lakes.     

APPLICATION OF A QUASI-2D HYDRO-MORPHOLOGICAL MODEL TO THE ARGENTINEAN PARAN(A) RIVER

Herein a simplified quasi-two dimensional horizontal hydro-morphological mathematical model is presented. The governing equations for the quasi-2D horizontal time-depending flow field are represented by the well-known approach of interconnected cells. New discharge laws between cells are incorporated. The model is capable of predicting temporal changes in water depth, velocity distribution,sediment transport, bed elevation, as well as water and suspended sediment exchanges between main stream and flood plains. An application of the model to the middle reach of the Argentinean Parana River is presented. Satisfactory results were obtained during model calibration, validation and application.     

The role of dew in the water and heat balance of bare loess soil in the Negev Desert: quantifying the actual dew deposition on the soil surface

During nighttime, latent heat fluxes to or from the soil surface are usually very small and the absolute amounts of dew deposition are accordingly very small. The detection of such small fluxes poses serious measurement difficulties. Various methods for measuring dew have been described in the literature and most of them rely on the use of artificial condensing plates with physical properties that are very different from those of soil surfaces. A system that detects the actual dew deposition on the soil surface under natural conditions would be advantageous and microlysimeters (MLs) appear to be the obvious answer. The objectives of this work were to test the adequacy of microlysimeters to estimate condensation amounts, and to compare these amounts with those measured by a Hiltner dew balance in order to validate the long term data collected using the latter. The research was carried out at the Wadi Mashash Experimental Farm in the Northern Negev, Israel, during two measurement periods. A micro-meteorological station was installed in the field next to a modified Hiltner balance. A microlysimeter with an undisturbed soil sample was placed nearby. During the first period, the depth of the microlysimeter was 15 cm while at the second period it was 55 cm. The results show that for measuring dew, the minimum depth of a microlysimeter should exceed the depth at which the diurnal temperature is constant, which for a dry loess soil in the Negev Desert is 50 cm.     

Rare-gas dating,III. Evaluation of a double-spiking procedure for potassium-argon dating

A double-spike method for KAr dating is described. Use of long-lived³⁹Ar in addition to the usual³⁸Ar in the spike permits argon isotopic discrimination occurring after insertion of the spike to be monitored at the same time as ages are determined. A “bootstrap” (self-contained) method of calibrating the spike for isotopic composition is described which, when used appropriately, gives final ages which are independent of the published isotopic composition of the terrestrial atmospheric argon used as a comparison gas. The method calls for a mass spectrometer which resolves adjacent isotopes to a high degree. We have tested the method nevertheless with a mass spectrometer of relatively low resolving power, the AEI MS-10, and found it to be successful in part and without any disadvantages with respect to conventional techniques in those instances where the method fails because of insufficient resolution. That is, we find the discrimination factor inferred in runs on young rocks and blanks to be valid and useful. That factor changes by as much as 1.3% over the life of a filament in the ion source of the MS-10, proving that close control of the discrimination factor is essential for analytical precision with the instrument. These assertions are documented graphically with a compilation of data which represents more than two years experience with the method. We also report measurements of the mass discrimination of the MS-10 and its linearity with mass which indicate that the latter quantity is acceptable when the repeller voltage for the ion source is close to +1 V and is unacceptable otherwise. The spike material is available, upon request, to those laboratories which decide firmly to undertake further testing of the method.     

From hard-path to soft-path solutions: slow–fast dynamics of human adaptation to droughts in a water scarce environment

ABSTRACT

Droughts have long impacted humans with adverse consequences, hindering the achievement of the United Nations Sustainable Development Goals. To reduce vulnerability, multiple ways of adaptation have been developed, most of which, historically, focused on “hard-path” implementation of infrastructure. However, since water consumption plays a major role in the supply–demand balance, “soft-path” solutions focusing on the control of water use have recently intensified. Furthermore, due to the dynamic interaction between humans and water, changes might occur over time, requiring adaptation measures to be continually reshaped. We assess the dynamic nature of human adaptation to droughts in the semi-arid Extended Jaguaribe Basin, Brazil. We explore the shift from hard, supply-oriented measures to soft governance, and its causes: natural and socio-economic processes not anticipated in the original water resources policy. The observed phenomenon and discussion of its causes help to build knowledge on human–water interactions that are applicable more generally.     

Impacts of land-use and climate changes on surface runoff in a tropical forest watershed (Brazil)

ABSTRACT

Surface runoff generation capacity can be modified by land-use and climate changes. Annual runoff volumes have been evaluated in a small watershed of tropical forest (Brazil), using the Soil and Water Assessment Tool (SWAT) model. Firstly, the accuracy of SWAT in runoff predictions has been assessed by default input parameters and improved by automatic calibration, using 20-year observations. Then, the hydrological response under land uses (cropland, pasture and deforested soil) alternative to tropical forest and climate change scenarios has been simulated. SWAT application has showed that, if forest was replaced by crops or pasture, the watershed’s hydrological response would not significantly be affected. Conversely, a complete deforestation would slightly increase its runoff generation capacity. Under forecasted climate scenarios, the runoff generation capacity of the watershed will tend to decrease and will not be noticeably different among the representative concentration pathways. Pasture and bare soil will give the lowest and highest runoff coefficients, respectively.     

Definition of geochemical patterns on the soil of Paul de Arzila using correspondence analysis

The aim of this study is to define geochemical and geological patterns, not only inside of Paul de Arzila natural reserve but in the surrounding area. The Correspondence Analysis was used as a discriminate technique to separate previously identified groups, in this case three types of soils (cambisols + luvisols + fluvisols). The purpose was to identify the main chemical association representative for the local types of soils. The results allow us to separate the chemical elements that are related to natural sources from the anthropogenic sources.     

Lower Aptian Subbetic organic-rich facies, radiolarites, and associated deposits: the local expression of Oceanic Anoxic Event 1a (Carbonero Formation, southern Spain)

The Carbonero Formation represents a scarce, well documented example of Aptian anoxic facies in the Betic Cordillera. Generally, the Aptian record in the pelagic Subbetic basin is both very discontinuous and affected by frequent hiatuses, but in some subsident areas controlled by extensional faults (as in the Carbonero trough) an interesting record is preserved. The Carbonero Formation is characterised by a thick pelagic succession composed of marls with intercalations of calcareous turbidites and a thick interval of anoxic facies. This interval, dated as early Aptian, most likely represents the local expression of Ocean Anoxic Event 1a in the Subbetic basin. A multidisciplinary study including lithostratigraphy, biostratigraphy, and sedimentology has been carried out in the Carbonero Formation, with special attention to the anoxic interval. A collection of facies and sedimentary features has been characterised and interpreted, including barite concretions, calcareous concretions, black shales, siliceous marls and radiolarites, and calcareous turbidites. All these facies seem to have been deposited under oxygen-depleted conditions on a fault-bounded depression with a high subsidence rate. The accumulation and burial of sediments and the preservation of organic matter were controlled by both local and regional factors, such as the physiography of the basin and tectonic setting, as well as by global factors, such as palaeoceanographic and climatic changes.     

Correction of TRMM 3B43 monthly precipitation data over the mountainous areas of Peru during the period 1998–2007

In an attempt to estimate the spatial and temporal behaviour of rainfall over the mountainous areas of the Peruvian Andes, a new in situ monthly rainfall dataset has been collected (1998–2007) and compared with Tropical Rainfall Measuring Mission (TRMM) 3B43 monthly precipitation data for regions located above 3000 m. The reliability of the TRMM 3B43 data varies depending on the root mean squared error ratio (%RMSE) and correlation coefficient. Because of the discrepancy between the two datasets, the use of additive and multiplicative correction models is proposed for the TRMM 3B43 data. In the Peruvian mountain ranges, these correction models better approximate TRMM rainfall monthly values, as already verified for annual values. Copyright © 2011 John Wiley & Sons, Ltd.