The role of hydrological processes in ecosystem conservation: Comprehensive water management for a wetland in an arid climate

Water agreements between Mexico and the United States have been crucial to preserving and restoring the Colorado River Delta's wetlands. Nowadays, increased water demand and climate change in the Colorado River Basin could threaten the conservation of the Ciénega de Santa Clara, a 4709 ha coastal wetland at the Sonoran Desert's edge. The international Ramsar convention recognizes the Ciénega de Santa Clara ecosystem for providing vital ecological services, including habitat for endemic, endangered, and migratory species. The hydrology of this wetland has not been completely understood since the 2010–2011 trial run of the Yuma Desalting Plant. Therefore, this study was conducted to identify and quantify the hydrological elements essential for the conservation of this wetland, under three scenarios: (a) normal inflow conditions of the water source – the Wellton-Mohawk canal; (b) inflow reductions, and; (c) an increase of temperature due to global warming. Water and mass balances estimates were conducted every month during 2014–2015; in situ measurements of inflows were carried out on Southern International Boundary in Wellton-Mohawk canal, the Riíto Drain, groundwater, and precipitation: evapotranspiration outputs were estimated using local weather stations and Penman-Monteith formulations. Temperature increases were based on the Intergovernmental Panel on Climate Change projections for the next 100 years. Results showed disconnection in the surface flow of water from the wetland to the adjacent Gulf of California. This behaviour was observed mainly in the summer months in the three scenarios. The disconnections reduced the wetland area and water storage. The hydrological functionality of the Ciénega de Santa Clara wetland depends on the water supply from the Wellton-Mohawk canal, with a minimum continuous discharge of 5.10 m³ s⁻¹ during the summer months.     

Determination of the Concentration of Carbonic Species in Natural Waters: Results from a World‐Wide Proficiency Test

The results of an international interlaboratory proficiency test for the determination of carbonic species are presented. Eight laboratories analysed twelve water samples (four synthetic waters, one lake water, four geothermal waters, one seawater and two petroleum waters) by two methods: (a) individual laboratory analytical procedure and (b) acid–base titration curves in tabular form following a standardised protocol. In case (b), the concentrations of carbonic species were calculated by the organiser using the (1) Hydrologists' method, (2) Geochemists' method and/or (3) initial pH and total alkalinity method. For synthetic waters, the averaged % trueness and precision of measurement of the two methods were (trueness = 7.6, precision = 9.4) and (9.0, 3.4) for total alkalinity, and (6.6, 31.0) and (7.8, 6.1) for carbonic alkalinity, respectively. This indicates that the total alkalinity calculation procedure is in general correct in the individual laboratory method, but the carbonic alkalinity calculation procedure has serious problems. The measurements of total alkalinity for lake and seawaters were in agreement in both the methods; however, the individual laboratory measurement method for geothermal and petroleum waters was conceptually incorrect. Thus, the analytical procedures for the determination of carbonic species were reviewed. To apply the Hydrologists' and/or Geochemists' methods, the location of NaHCO₃EP and H₂CO₃EP is necessary, even for samples with pH lower than that of NaHCO₃EP, and a backward titration curve after complete removal of CO₂ must be performed. The initial pH and total alkalinity method is appropriate where a complete analysis of species that contribute to the alkalinity is known.     

Probabilistic modelling of auto-correlation characteristics of heterogeneous slopes

Spatial variability of soil materials has long been recognised as an important factor influencing the reliability of geo-structures. This study stochastically investigates the influence of spatial variability of shear strength on the stability of heterogeneous slopes, focusing on the auto-correlation function, auto-correlation distance and cross-correlation between soil parameters. The finite element method is merged with the random field theory to probabilistically evaluate factor of safety and probability of failure via Monte-Carlo simulations. The simulation procedure is explained in detail with suggestions on improving efficiency of the Monte-Carlo process. A simple procedure to create cross-correlation between random variables, which allows direct comparison of the influence of each strength variable, is discussed. The results show that the auto-correlation distance and cross-correlation can significantly influence slope stability, while the choice of auto-correlation function only has a minor effect. An equation relating the probability of failure with the auto-correlation distance is suggested in light of the analyses performed in this work and other results from the literature.     

Combined effects of elevated [CO2] and high temperature on leaf mineral balance in Coffea spp. plants

Modelling studies predicted that climate change will have strong impacts on the coffee crop, although no information on the effective impact of elevated CO₂ on this plant exists. Here, we aim at providing a first glimpse on the effect of the combined impact of enhanced [CO₂] and high temperature on the leaf mineral content and balance on this important tropical crop. Potted plants from two genotypes of Coffea arabica (cv. Icatu and IPR 108) and one from C. canephora (cv. Conilon Clone 153) were grown under 380 or 700 μL CO₂ L^?1 air, for 1 year, after which were exposed to an stepwise increase in temperature from 25/20 °C (day/night) up to 42/34 °C, over 8 weeks. Leaf macro???(N, P, K, Ca, Mg, S) and micronutrients (B, Cu, Fe, Mn, Zn) concentrations were analyzed at 25/20 °C (control), 31/25 °C, 37/30 °C and 42/34 °C. At the control temperature, the 700 μL L^?1 grown plants showed a moderate dilution effect (between 7 % and 25 %) in CL 153 (for N, Mg, Ca, Fe) and Icatu (for N, K and Fe), but not in IPR 108 (except for Fe) when compared to the 380 μL L^?1 plants. For temperatures higher than control most nutrients tended to increase, frequently presenting maximal contents at 42/34 °C (or 37/30 °C), although the relation between [CO₂] treatments did not appreciably change. Such increases offset the few dilution effects observed under high growth [CO₂] at 25/20 °C. No clear species responses were found considering [CO₂] and temperature impacts, although IPR 108 seemed less sensitive to [CO₂]. Despite the changes promoted by [CO₂] and heat, the large majority of mineral ratios were kept within a range considered adequate, suggesting that this plant can maintain mineral balances in a context of climate changes and global warming.     

Spatiotemporal analysis of particulate matter, sulfur dioxide and carbon monoxide concentrations over the city of Rio de Janeiro, Brazil

Time series of pollutants and weather variables measured at four sites in the city of Rio de Janeiro, Brazil, between 2002 and 2004, were used to characterize temporal and spatial relationships of air pollution. Concentrations of particulate matter (PM₁₀), sulfur dioxide (SO₂) and carbon monoxide (CO) were compared to national and international standards. The annual median concentration of PM₁₀ was higher than the standard set by the World Health Organization (WHO) on all sites and the 24?h means exceeded the standards on several occasions on two sites. SO₂ and CO did not exceed the limits, but the daily maximum of CO in one of the stations was 27% higher on weekends compared to weekdays, due to increased activity in a nearby Convention Center. Air temperature and vapor pressure deficit have both presented the highest correlations with pollutant??s concentrations. The concentrations of SO₂ and CO were not correlated between sites, suggesting that local sources are more important to those pollutants compared to PM₁₀. The time series of pollutants and air temperature were decomposed in time and frequency by wavelet analysis. The results revealed that the common variability of air temperature and PM₁₀ is dominated by temporal scales of 1?C8?days, time scales that are associated with the passage of weather events, such as cold fronts.     

Late Quaternary paleoenvironments and paleoclimatic conditions in the distal Andean piedmont, southern Mendoza, Argentina

The Andean piedmont of Mendoza is a semiarid region covered by extensive and partially vegetated dune fields consisting of mostly inactive aeolian landforms of diverse size and morphology. This paper is focused on the San Rafael plain (SRP) environment, situated in the distal Andean piedmont of Mendoza (34° 30′S), and reports the sedimentology and OSL chronology of two representative exposures of late Quaternary deposits, including their paleoenvironmental and paleoclimatic significance. Eleven facies, including channel, floodplain, fluvio–aeolian interaction, and reworked pyroclastic and aeolian deposits, were described and grouped into two facies associations (FA1 and FA2). FA1 was formed by unconfined sheet flows, minor channelized streams and fluvial–aeolian interaction processes. FA2 was interpreted as aeolian dune and sand-sheet deposits. OSL chronology from the SRP sedimentary record indicates that between ca. 58–39 ka and ca. 36–24 ka (MIS 3), aggradation was governed by ephemeral fluvial processes (FA1) under generally semiarid conditions. During MIS 2, the last glacial maximum (ca. 24–12 ka), a major climatic shift to more arid conditions is documented by significant aeolian activity (FA2) that became the dominant sedimentation process north of the Diamante–Atuel fluvial system. The inferred paleoenvironmental conditions from the SRP sections are in broad agreement with regional evidence.     

Triterpenols in mangrove sediments as a proxy for organic matter derived from the red mangrove (Rhizophora mangle)

Mangroves are the dominant type of vegetation along many tropical coasts. Organic matter (OM) derived from mangrove leaf litter and root material is stored in sediments and is a major contributor to the amount and chemical composition of sedimentary OM. A set of organic biomarkers in sediments was applied as a palaeo-indicator for the Holocene dynamics of a mangrove Estuary (Rio Caeté, Pará, Brazil). Six sediment cores were collected perpendicular to the present coast line and analysed for triterpenols and sitosterol. The influence of microbial biomarker degradation was implemented from a previous study. Biomarker profiles were validated with pollen data and multivariate statistics to test whether these compounds were suitable indicators for the palaeo-vegetation. Sediments deposited up to 2 Ma BP showed biomarker assemblages similar to those of recent surface sediment. In two cores, the biomarker composition revealed a transition from marsh to mangrove vegetation. Taraxerol, germanicol and β-amyrin provided the most significant chemotaxonomical information and, especially in combination, served as reliable proxies for OM from Rhizophora mangle in northern Brazil. The maximum age of the mangrove system ranged between 1000 and 5100 yr depending on the topographic elevation of the drilling location.     

New chelid turtles of the lower section of the Cerro Barcino formation (Aptian-Albian?), Patagonia, Argentina

A new chelid species (Prochelidella cerrobarcinae nov. sp.) are described from the Aptian-Albian? Puesto La Paloma Member, Cerro Barcino Formation, northern of Chubut Province, Argentina. The basal section of this member, which bears the turtle remains, is composed of tuffaceous mudstones with plane parallel lamination, asymmetrical ripples and a chert intercalation suggesting sub-aqueous deposition in a relatively shallow lacustrine environment. Pr. cerrobarcinae nov. sp. is represented by post-cranial remains of several specimens that not only represents the oldest pleurodiran chelid record in the world but, together with the chelid remains of Albian Lightning Ridge, New South Wales, Australia, indicates that chelid diversification began well before the final fragmentation of southern Gondwana.     

A 3-D lithospheric model of the Caribbean-South American plate boundary

A 3-D structural model of the Caribbean-South American plate boundary was constructed by gravity modeling. The model was constrained by four wide-angle seismic refraction sections, Moho depth estimations from receiver functions, and additionally seismological hypocenters, surface geology, and geodynamic information. Density values were calculated from empirical velocity-density functions, and mineralogical-chemical composition considering specific P/T conditions. We tested different structural models for Western and Eastern Venezuela. In the final model, the fit of the measured and modeled gravity fields for a long Caribbean slab in Western Venezuela was better than the fit obtained for a short one. This interpretation is consistent with the constraining data. The slab is interpreted to extend further to the south beneath Northern Colombia and culminates in the area of the seismic cluster of the Bucaramanga nest. The modeling estimates a slab dip angle under Maracaibo and Mérida Andes of 15°, which increases to 32° below 100 km depth. The dip direction of approx. N150°E ± 5 increases lightly eastward. In Eastern Venezuela, considering its short wavelength, lineaments analyzed from gravity data (by curvature methods and Euler deconvolution) seem to be related to shallow structures and density contrast in the Serranía del Interior and not from a deep detached slab beneath the continental crust. It is deduced from modeling results that this slab configuration has a very small influence on the gravity field. The slab was modeled according to the subduction-transform propagation model with purely westward subduction and a slab break off along a vertical dip-slip tear through the lithosphere.