Spatiotemporal estimation of snow depth using point data from snow stakes,digital terrain models,and satellite data

Snow availability in Alpine catchments plays an important role in water resources management. In this paper, we propose a method for an optimal estimation of snow depth (areal extension and thickness) in Alpine systems from point data and satellite observations by using significant explanatory variables deduced from a digital terrain model. It is intended to be a parsimonious approach that may complement physical‐based methodologies. Different techniques (multiple regression, multicriteria analysis, and kriging) are integrated to address the following issues: We identify the explanatory variables that could be helpful on the basis of a critical review of the scientific literature. We study the relationship between ground observations and explanatory variables using a systematic procedure for a complete multiple regression analysis. Multiple regression models are calibrated combining all suggested model structures and explanatory variables. We also propose an evaluation of the models (using indices to analyze the goodness of fit) and select the best approaches (models and variables) on the basis of multicriteria analysis. Estimation of the snow depth is performed with the selected regression models. The residual estimation is improved by applying kriging in cases with spatial correlation. The final estimate is obtained by combining regression and kriging results, and constraining the snow domain in accordance with satellite data. The method is illustrated using the case study of the Sierra Nevada mountain range (Southern Spain). A cross‐validation experiment has confirmed the efficiency of the proposed procedure. Finally, although it is not the scope of this work, the snow depth is used to asses a first estimation of snow water equivalent resources.     

Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.     

9000 years of changes in peat organic matter composition in Store Mosse (Sweden) traced using FTIR-ATR

Store Mosse (the ‘Great Bog’ in Swedish) is one of the most extensive bog complexes in southern Sweden (~77 km²), where pioneering palaeoenvironmental research has been carried out since the early 20th century. This includes, for example, vegetation changes, carbon and nitrogen dynamics, peat decomposition, atmospheric metal pollution, mineral dust deposition, dendrochronology, and tephrochronology. Even though organic matter (OM) represents the bulk of the peat mass and its compositional change has the potential to provide crucial ecological information on bog responses to environmental factors, peat OM molecular composition has not been addressed in detail. Here, a 568-cm-deep peat sequence was studied at high resolution, by attenuated reflectance Fourier-transform infrared spectroscopy (FTIR-ATR) in the mid-infrared region (4000–400 cm^–1). Principal components analysis was performed on selected absorbances and change-point modelling was applied to the records to determine the timing of changes. Four components accounted for peat composition: (i) depletion/accumulation of labile (i.e. carbohydrates) and recalcitrant (i.e. lignin and other aromatics, aliphatics, organic acids and some N compounds) compounds, due to peat decomposition; (ii) variations in N compounds and carbohydrates; (iii) residual variation of lignin and organic acids; and (iv) residual variation of aliphatic structures. Peat decomposition showed two main patterns: a long-term trend highly correlated to peat age (r = 0.87), and a short-term trend, which showed five main phases of increased decomposition (at ~8.4–8.1, ~7.0–5.6, ~3.5–3.1, ~2.7–2.1 and ~1.6–1.3 ka) – mostly corresponding to drier climate and its effect on bog hydrology. The high peat accumulation event (~5.6–3.9 ka), described in earlier studies, is characterized by the lowest degree of peat decomposition of the whole record. Given that FTIR-ATR is a quick, non-destructive, cost-effective technique, our results indicate that it can be applied in a systematic way (including multicore studies) to peat research and provide relevant information on the evolution of peatlands.     

The geography of multiple scarcities: Urban development and water problems in Lima,Peru

The paper discusses the contradictory evolution of water services and the politicised nature of water scarcity in Lima, the capital of Peru. It initially claims that water scarcity cannot be understood as an isolated phenomenon, but it is inserted in a wider multiplicity of scarcities that characterise contemporary urban development. The naturalisation of scarcity in the official policy discourse is then criticised for its tendency to overlook interconnected mechanisms of political differentiation and socioeconomic exploitation that influence the allocation and use of water. Against such reductionist readings, the analysis employs a non-essentialist interpretation of multiple scarcities related to water and emphasises the need to address the totality of the experience of scarcity. Based on qualitative fieldwork, which explored recent institutional reforms and the daily struggle for water in the periphery of Lima, three fundamental reasons were identified for the persistence of water scarcity: first, the expansion of water problems as a result of the poor quality of housing and the discriminatory practices against low-income residents; second, the modest improvements in water services provided by public investment programmes, which have primarily aimed to answer political and electoral demands of the ruling party; and third, the technocratic basis of new management approaches and the systematic exclusion of grassroots communities from the decision-making process. Genuine responses to the mounting water problems of Lima require a more critical appreciation of the production of circumstantial abundances and totalising scarcities in the city.     

Impact of irrigated agriculture on groundwater-recharge salinity: a major sustainability concern in semi-arid regions

Intensive irrigated agriculture substantially modifies the hydrological cycle and often has major environmental impacts. The article focuses upon a specific concern—the tendency for progressive long-term increases in the salinity of groundwater recharge derived from irrigated permeable soils and replenishment of unconfined aquifers in more arid regions. This process has received only scant attention in the water-resource literature and has not been considered by agricultural science. This work makes an original contribution by analysing, from scientific principles, how the salinisation of groundwater recharge arises and identifies the factors affecting its severity. If not proactively managed, the process eventually will impact irrigation waterwell salinity, the productivity of agriculture itself, and can even lead to land abandonment. The types of management measure required for mitigation are discussed through three detailed case histories of areas with high-value groundwater-irrigated agriculture (in Spain, Argentina and Pakistan), which provide a long-term perspective on the evolution of the problem over various decades.     

Tide-Induced Variations in the Fatty Acid Composition of Estuarine Particulate Organic Matter

The particulate organic matter (POM) in hydrodynamically variable habitats such as the lower reaches of estuaries can change in its content and quality on very short time scales (example, hourly), and these changes can potentially influence higher-level consumers in river-estuary-marine systems. Estuarine water samples were collected hourly for 12 h downstream in a small river to evaluate the fatty acid composition of POM over a tidal cycle. Fatty acid constituents of POM collected during the flood tide were dominated by the saturated, higher plant and bacterial fatty acids, whereas unsaturated, polyunsaturated, essential, and diatom-associated fatty acids dominated the POM collected during the ebb tide. Elevated algal biomass (as indicated by high chlorophyll a concentrations), diatom, and freshness indices in the POM indicated enhanced fresh autochthonous-origin materials that dominated the mixed organic pool during the ebb tide compared to more degraded detritus during the flood tide. Tidal retention of organic matter and algal primary production were the most influential factors that differentiated the fatty acid composition of estuarine POM over the short time scale. The results of this study have important implications on the quality of POM at the time of sampling, especially in estuaries where mixed organic pools have multiple inputs and are strongly influenced by tidal cycles.     

K–Ar and Ar/Ar ages of dikes emplaced in the onshore basement of the Santos Basin, Resende area, SE Brazil: implications for the south Atlantic opening and Tertiary reactivation

New K–Ar and ⁴⁰Ar/³⁹Ar data of tholeiitic and alkaline dike swarms from the onshore basement of the Santos Basin (SE Brazil) reveal Mesozoic and Tertiary magmatic pulses. The tholeiitic rocks (basalt, dolerite, and microgabbro) display high TiO₂ contents (average 3.65 wt%) and comprise two magmatic groups. The NW-oriented samples of Group A have (La/Yb)_N ratios between 15 and 32.3 and range in age from 192.9±2.2 to 160.9±1.9 Ma. The NNW-NNE Group B samples, with (La/Yb)_N ratios between 7 and 16, range from 148.3±3 to 133.9±0.5 Ma. The alkaline rocks (syenite, trachyte, phonolite, alkaline basalts, and lamprophyre) display intermediate–K contents and comprise dikes, plugs, and stocks. Ages of approximately 82 Ma were obtained for the lamprophyre dikes, 70 Ma for the syenite plutons, and 64–59 Ma for felsic dikes. Because Jurassic–Early Cretaceous basic dikes have not been reported in SE Brazil, we might speculate that, during the emplacement of Group A dikes, extensional stresses were active in the region before the opening of the south Atlantic Ocean and coeval with the Karoo magmatism described in South Africa. Group B dikes yield ages compatible with those obtained for Serra Geral and Ponta Grossa magmatism in the Paraná Basin and are directly related to the breakup of western Gondwana. Alkaline magmatism is associated with several tectonic episodes that postdate the opening of the Atlantic Ocean and related to the upwelling of the Trindade plume and the generation of Tertiary basins southeast of Brazil. In the studied region, alkaline magmatism can be subdivided in two episodes: the first one represented by lamprophyre dykes of approximately 82 Ma and the second comprised of felsic alkaline stocks of approximately 70 Ma and associated dikes ranging from 64 to 59 Ma.

Resumo

Novos dados K–Ar e ⁴⁰Ar/³⁹Ar de enxames de diques toleíticos e alcalinos localizados no embasamento onshore da Bacia de Santos (SE Brasil) apontam para diferentes pulsos magmáticos ocorridos entre o Jurássico e o Terciário. Os diques de rochas toleíticas (basalto, diabásio e microgabro), são mais velhos, exibem altos teores de TiO₂ (3,65% peso na média) e podem ser subdivididos em dois grupos magmáticos. O Grupo A aflora a norte da Bacia de Resende, compreende diques orientados na direção NW, com razões (La/Yb)_N entre 15 e 32,3, e idades entre 192.9±2.2 e 160.9±1.9 Ma. O Grupo B aflora a sul e a leste da Bacia de Resende, engloba diques orientados na direção NNW e NNE, com razões (La/Yb)_N entre 7 e 16, e idades obtidas entre 148.3±3 e 133.9±0.5 Ma. As rochas alcalinas (sienito, traquito, fonolito, basalto alcalino e lamprófiro) possuem teores médios de K, e afloram como diques, plugs e stocks.. As idades obtidas são de ca. 82 Ma para os diques lamprofíricos, de ca. 70 Ma para os plugs sieníticos, e entre 64 e 59 Ma para os diques félsicos. Como estas idades Jurássicas para diques toleíticos ainda não foram descritas para a região sudeste do Brasil, pode-se especular que durante o emplacement dos diques do GrupoA o cenário tectônico indicaria esforços extensionais anteriores à abertura do Oceano atlântico Sul, e contemporânea ao derrame basáltico do Karoo na África do Sul. Já os diques do Grupo B são contemporâneos ao magmatismo Serra Geral e ao enxame de diques de Ponta Grossa, e portanto este episódio está diretamente relacionado à separação entre o Brasil e África no Cretáceo. O magmatismo alcalino está associado a diversos episódios tectônicos que sucedem à abertura do Oceano Atlântico Sul e que resultaram no desenvolvimento das Bacias terciárias do sudeste brasileiro. Está provavelmente relacionado à chegada da Pluma de Trindade e as idades obtidas para a região em estudo indicam que o magmatismo lamprofírico é mais antigo (ca. 82 Ma), seguido pelos plútons sieníticos (ca. 70 Ma) e diques associados (64 a 59 Ma.)     

Multi-Modal Monitoring of Slip Along Frictional Discontinuities

Seismic wave transmission and digital image correlation (DIC) are employed to study slip processes along frictional discontinuities. A series of biaxial compression experiments are performed on gypsum specimens with non-homogeneous contact surfaces. The specimens are composed of two blocks with perfectly mated contact surfaces with a smooth surface with low frictional strength on the upper half and a rough surface with high frictional strength on the lower half. Compressional, P, and shear, S, wave pulses were transmitted through the discontinuity while digital images of the specimen surface were acquired during the test. A distinct peak in the amplitude of transmitted wave occurs prior to the peak shear strength and is considered a “precursor” to the failure. Precursors indicate that slip initiates from the smooth surface and extends to the rough surface as the shear load is increased. From the DIC data, slip is identified as a jump in the displacement field along the fracture that initiates from the smooth surface and propagates to the rough surface. Precursors are associated with an increase in the rate of slip across the discontinuity and are a measure of the reduction in the fracture shear stiffness.     

Kinetics of reactions between aqueous sulfates and sulfides in hydrothermal systems

The rates of chemical reactions between aqueous sulfates and sulfides are essentially identical to sulfur isotopic exchange rates between them, because both the chemical and isotopic reactions involve simultaneous oxidation of sulfide-sulfur atoms and reduction of sulfate-sulfur. The rate of reaction can be expressed as a second order rate law: R = k·[∑SO₄^2?]·[∑S^2?], where R is the overall rate, k is the rate constant and [∑SO₄^2?] and [∑S^2?] are molal concentrations. We have computed the rate constants from the available experimental data on the partial exchange of sulfur isotopes between aqueous sulfates and sulfides using the rate law established by us: $\text{ln(}\text{α}{}^{\mathrm{e}}\text{? α}\text{α}{}^{\mathrm{e}}\text{? α}{}^0\text{) = ? kt([∑SO}{}_4{}^{\mathrm{2?}}\text{] + [∑S}{}^{\mathrm{2?}}\text{])}$, where t is time and α⁰, α, and α^e are, respectively, the fractionation factors at t = 0 (the initial condition), at the end of experiment, and at equilibrium. The equilibrium fractionation factor can be expressed as: $\text{1000 ln α}{}^{\mathrm{e}}\text{=}\text{6.463 × 10}{}^6\text{T}{}^2\text{+ 0.56 (±.5)}$ (T in Kelvin).The rate constants are strongly dependent on T and pH, but not in as simple a manner as suggested by Igumnov (1976). Our rate constants in Na-bearing hydrothermal solutions decrease by 1 order of magnitude with an increase in pH by 1 unit at pH's less than ~3, remain constant in the pH range of ~4 to ~7, and again decrease at pH >7. The activation energy for the reaction also depends on pH: 18.4 ± 1 kcal/mole at pH = 2, 29.6 ± 1 kcal/mole at pH = 4 to 7, and between 40 and 47 kcal/mole at pH around 9. The observed pH dependence of the rate constant and of the activation energy can be best explained by a model involving thiosulfate molecules as reaction intermediates, in which the intramolecular exchange of sulfur atoms in thiosulfates becomes the rate determining step.The rate constants obtained in this study were used to compute the changes in the isotopic fractionation factors between aqueous sulfates and sulfides during cooling of fluids. Comparisons with data of coexisting sulfate-sulfide minerals in hydrothermal deposits, suggest that simple cooling was not a likely mechanism for coprecipitation of sulfate and sulfide minerals at temperatures below 350°C. Mixing of sulfide-rich solutions with sulfate-rich solutions at or near the depositional sites is a more reasonable process for explaining the observed fractionation.The degree of attainment of chemical equilibrium between aqueous sulfates and sulfides in a hydrothermal system, and the applicability of a_O2-pH type diagrams to mineral deposits, depends on the ∑S content and the thermal history of the fluid, which in turn is controlled by the flow rate and the thermal gradient in the system.The rates of sulfate reduction by non-bacterial processes involving a variety of reductants are also dependent on T, pH, [∑SO₄^2?], and [∑S^2?], and appear to be fast enough to become geochemically important at temperatures above about 200°C.