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The biostratigraphy of Campanian-Maastrichtian carbonate platforms is largely based on the larger foraminiferal genus Orbitoides. However, while the taxonomy and the chronostratigraphic age of the younger species of this genus are well established, there are still many controversies on the earliest species. We have restudied their morphological characters using a large collection of samples from the type-localities and from continuous sections in the southern Pyrenees. Based on these new observations, the long forgotten species O. sanctae-pelagiae is reinstated, while O. dordoniensis is considered a junior synonym. Successive populations of O. hottingeri, O. sanctae-pelagiae and O. douvillei show gradual morphological changes in time marked by an increase in the size and complexity of the macrospheric embryonal apparatus, an increase of the size of the adult specimens of both generations and the progressive appearance and development of true lateral chamberlets. The Font de les Bagasses Unit in the southern Pyrenees preserves a high-resolution archive of the evolution of the earliest Orbitoides. Strontium isotope stratigraphy indicates that the oldest species, O. hottingeri, made its first appearance in the earliest Campanian, close to the Santonian-Campanian boundary, and was replaced by O. sanctae-pelagiae at a level closely corresponding to the boundary between the Placenticeras bidorsatum and Menabites delawarensis ammonite zones. (C) 2014 Elsevier Ltd. All rights reserved.
From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November-March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the "long rain" season (March-May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June-October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light-dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Nino-Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa.
The study presents the first evidence of metamorphosed submarine ashes in the Edough Massif, in northeastern Algeria. It occurs below the greenschist-facies Tellian units that represent the thrusted Mesozoic to Eocene passive paleomargin of northern Africa deposited on thinned continental crust. The metamorphic complex consists of tectonically superposed units composed of gneisses (lower unit) and micaschists (upper unit). At the Cap de Garde, these units enclose an "intermediate unit" composed of micaschists and meter-thick layers of marbles, which are sometimes intercalated with amphibolites. The latter occur as discontinuous small lenses and layers. The amphibolites are parallel to the primary bedding of the marbles and the main foliation. Chemical markers and field observations indicate that they are metamorphic equivalents of basic igneous rocks. The lenticular character, low thickness and multiple intercalations with marine sediments and the unusual high lithium concentrations suggest subaqueous near-source basaltic ash-fall deposits in a marine environment. (C) 2014 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Modification of the landscape by glacial erosion reflects the dynamic interplay of climate through temperature, precipitation, and prevailing wind direction, and tectonics through rock uplift and exhumation rate, lithology, and range and fault geometry. We investigate these relationships in the northeast Pamir Mountains using mapping and dating of moraines and terraces to determine the glacial history. We analyze modem glacial morphology to determine glacier area, spacing, headwall relief, debris cover, and equilibrium line altitude (ELA) using the area x altitude balance ratio (AABR), toe-to-headwall altitude ratio (THAR) and toe-to-summit altitude method (TSAM) for 156 glaciers and compare this to lithologic, tectonic, and climatic data We observe a pronounced asymmetry in glacial ELA, area, debris cover, and headwall relief that we interpret to reflect both structural and climatic control: glaciers on the downwind (eastern) side of the range are larger, more debris covered, have steeper headwalls, and tend to erode headward, truncating the smaller glaciers of the upwind, fault-controlled side of the range. We explain this by the transfer of moisture deep into the range as wind-blown or avalanched snow and by limitations imposed on glacial area on the upwind side of the range by the geometry of the Kongur extensional system (KES). The correspondence between rapid exhumation along the KES and maxima in glacier debris cover and headwall relief and minimums in all measures of ELA suggest that taller glacier headwalls develop in a response to more rapid exhumation rates. However, we find that glaciers in the Muji valley did not extend beyond the range front until at least 43 ka, in contrast to extensive glaciation since 300 ka in the south around the high peaks, a pattern which does not clearly reflect uplift rate. Instead, the difference in glacial history and the presence of large peaks (Muztagh Ata and Kongur Shan) with flanking glaciers likely reflects lithologic control (i.e., the location of crustal gneiss domes) and the formation of peaks that rise above the ELA and escape the glacial buzzsaw. (C) 2014 Elsevier B.V. All rights reserved.
We present the results of biogeochemical and mineralogical analyses on a sediment core that covers the Holocene sedimentation history of the climatically sensitive, closed, saline, and alkaline Lonar Lake in the core monsoon zone in central India. We compare our results of C/N ratios, stable carbon and nitrogen isotopes, grain-size, as well as amino acid derived degradation proxies with climatically sensitive proxies of other records from South Asia and the North Atlantic region. The comparison reveals some more or less contemporaneous climate shifts. At Lonar Lake, a general long term climate transition from wet conditions during the early Holocene to drier conditions during the late Holocene, delineating the insolation curve, can be reconstructed. In addition to the previously identified periods of prolonged drought during 4.6-3.9 and 2.0-0.6 cal ka that have been attributed to temperature changes in the Indo Pacific Warm Pool, several additional phases of shorter term climate alteration superimposed upon the general climate trend can be identified. These correlate with cold phases in the North Atlantic region. The most pronounced climate deteriorations indicated by our data occurred during 62-5.2,4.6-3.9, and 2.0-0.6 cal ka BP. The strong dry phase between 4.6 and 3.9 cal ka BP at Lonar Lake corroborates the hypothesis that severe climate deterioration contributed to the decline of the Indus Civilisation about 3.9 ka BP. (C) 2014 Elsevier B.V. All rights reserved.
Late Holocene glacier variations in westernmost Tibetan Plateau were studied based on the analysis of grain size, magnetic susceptibility, and elements from an 8.3m long distal glaciolacustrine sediment core of Kalakuli Lake. Our results show that there are four glacier expansion episodes occurring in 4200-3700calibrated years (cal years) B.P., 2950-2300cal years B.P., 1700-1070cal years B.P., and 570-100cal years B.P. and four glacier retreat periods of 3700-2950cal years B.P., 2300-1700cal years B.P., 1070-570cal years B.P., and 50cal years B.P.-present. The four glacier expansion episodes are generally in agreement with the glacier activities indicted by the moraines at Muztagh Ata and Kongur Shan, as well as with the late Holocene ice-rafting events in the North Atlantic. Over the last 2000years, our reconstructed glacier variations are in temporal agreement with reconstructed temperature from China and the Northern Hemisphere, indicating that glacier variations at centennial time scales are very sensitive to temperature in western Tibetan Plateau.
The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and their response to enhanced greenhouse conditions such as those in the Eocene period (55-34Myrago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.
The cultivation of plants for use as energy resources is an agricultural and industrial sector with potentially synergistic benefits related to protecting the environment and generating income. Against the background of increasing land-use changes and new agricultural approaches to the production of energy crops, we present a method for identifying future-oriented crop rotations that supports both the economic and environmental components of decision-making strategies with respect to agriculture-related policy decisions (regional mission statements). The conflicting aspects of these objectives can be addressed with the analytic hierarchy process (AHP), a multi-attribute decision-making method that was integrated here. Three models are used to generate simulations of the defined objectives over a planning period of 30 years under the current climate scenario and provide input data for the multi-attribute assessment of several crop rotations. Based on the entire evaluation process, dimensionless global priority vectors are used to indicate how well the crop rotations meet the requirements of the defined mission statement. The method is tested in a municipality in NE Germany. (C) 2014 Elsevier Ltd. All rights reserved.
Within the framework of the international DESIRE (DEad Sea Integrated REsearch) project, a dense temporary local seismological network was operated in the southern Dead Sea area. During 18 recording months, 648 events were detected. Based on an already published tomography study clustering, focal mechanisms, statistics and the distribution of the microseismicity in relation to the velocity models from the tomography are analysed. The determined b value of 0.74 leads to a relatively high risk of large earthquakes compared to the moderate microseismic activity. The distribution of the seismicity indicates an asymmetric basin with a vertical strike-slip fault forming the eastern boundary of the basin, and an inclined western boundary, made up of strike-slip and normal faults. Furthermore, significant differences between the area north and south of the Bokek fault were observed. South of the Bokek fault, the western boundary is inactive while the entire seismicity occurs on the eastern boundary and below the basin-fill sediments. The largest events occurred here, and their focal mechanisms represent the northwards transform motion of the Arabian plate along the Dead Sea Transform. The vertical extension of the spatial and temporal cluster from February 2007 is interpreted as being related to the locking of the region around the Bokek fault. North of the Bokek fault similar seismic activity occurs on both boundaries most notably within the basin-fill sediments, displaying mainly small events with strike-slip mechanism and normal faulting in EW direction. Therefore, we suggest that the Bokek fault forms the border between the single transform fault and the pull-apart basin with two active border faults.
AimFossil pollen spectra from lake sediments in central and western Mongolia have been used to interpret past climatic variations, but hitherto no suitable modern pollen-climate calibration set has been available to infer past climate changes quantitatively. We established such a modern pollen dataset and used it to develop a transfer function model that we applied to a fossil pollen record in order to investigate: (1) whether there was a significant moisture response to the Younger Dryas event in north-western Mongolia; and (2) whether the early Holocene was characterized by dry or wet climatic conditions.
LocationCentral and western Mongolia.
MethodsWe analysed pollen data from surface sediments from 90 lakes. A transfer function for mean annual precipitation (P-ann) was developed with weighted averaging partial least squares regression (WA-PLS) and applied to a fossil pollen record from Lake Bayan Nuur (49.98 degrees N, 93.95 degrees E, 932m a.s.l.). Statistical approaches were used to investigate the modern pollen-climate relationships and assess model performance and reconstruction output.
ResultsRedundancy analysis shows that the modern pollen spectra are characteristic of their respective vegetation types and local climate. Spatial autocorrelation and significance tests of environmental variables show that the WA-PLS model for P-ann is the most valid function for our dataset, and possesses the lowest root mean squared error of prediction.
Main conclusionsPrecipitation is the most important predictor of pollen and vegetation distributions in our study area. Our quantitative climate reconstruction indicates a dry Younger Dryas, a relatively dry early Holocene, a wet mid-Holocene and a dry late Holocene.
Our study presents the results of a moment tensor inversion of 19 microseismic events with M-L between 2.0 and 3.4, associated with the stimulation operation of an enhanced geothermal reservoir in Basel, Switzerland, in 2006. We adopt a three-step procedure to retrieve point source solution parameters based on full waveform inversion. The inversion is performed by fitting displacement amplitude spectra and displacement seismograms in the first and second step, respectively, assuming a double couple source model and thus obtaining focal solutions for all 19 events. Our results are in agreement with focal mechanisms from a previous study, which employed P wave first-motion polarities from more than 40 stations, whereas our solutions are achieved using full waveform data recorded by less than 10 surface stations. In the last step, a full moment tensor inversion is performed. The results from the moment tensor inversion show an improvement on the waveform fitting compared to the double couple models, which is verified by an F-test. We investigate the stability of the moment tensor solutions by employing different velocity models. The isotropic components of the moment tensor solutions of some events are not negligible, suggesting source volume changes due to fluid injection. Events with significant isotropic components occurred mainly during the stimulation phase and close to the injection well. On the other hand, events that occurred in the post-stimulation phase are predominantly pure shear failure and located further away from the well bore. These spatio-temporal patterns can be explained by the influence of pore pressure variations during and after the hydraulic stimulation at the geothermal site. (C) 2014 Elsevier Ltd. All rights reserved.
Trees and shrubs in tropical Africa use the C-3 cycle as a carbon fixation pathway during photosynthesis, while grasses and sedges mostly use the C-4 cycle. Leaf-wax lipids from sedimentary archives such as the long-chain n-alkanes (e.g., n-C-27 to n-C-33) inherit carbon isotope ratios that are representative of the carbon fixation pathway. Therefore, n-alkane delta C-13 values are often used to reconstruct past C-3/C-4 composition of vegetation, assuming that the relative proportions of C-3 and C-4 leaf waxes reflect the relative proportions of C-3 and C-4 plants. We have compared the delta C-13 values of n-alkanes from modern C-3 and C-4 plants with previously published values from recent lake sediments and provide a framework for estimating the fractional contribution (areal-based) of C-3 vegetation cover (f(C3)) represented by these sedimentary archives. Samples were collected in Cameroon, across a latitudinal transect that accommodates a wide range of climate zones and vegetation types, as reflected in the progressive northward replacement of C-3-dominated rain forest by C-4-dominated savanna. The C-3 plants analysed were characterised by substantially higher abundances of n-C-29 alkanes and by substantially lower abundances of n-C-33 alkanes than the C-4 plants. Furthermore, the sedimentary delta C-13 values of n-C-29 and n-C-31 alkanes from recent lake sediments in Cameroon (-37.4%) to 26.5%) were generally within the range of delta C-13 values for C-3 plants, even when from sites where C-4 plants dominated the catchment vegetation. In such cases simple linear mixing models fail to accurately reconstruct the relative proportions of C-3 and C-4 vegetation cover when using the delta C-13 values of sedimentary n-alkanes, overestimating the proportion of C-3 vegetation, likely as a consequence of the differences in plant wax production, preservation, transport, and/or deposition between C-3 and C-4 plants. We therefore tested a set of non-linear binary mixing models using delta C-13 values from both C-3 and C-4 vegetation as end-members. The non-linear models included a sigmoid function (sine-squared) that describes small variations in the f(C3) values as the minimum and maximum delta C-13 values are approached, and a hyperbolic function that takes into account the differences between C-3 and C-4 plants discussed above. Model fitting and the estimation of uncertainties were completed using the Monte Carlo algorithm and can be improved by future data addition. Models that provided the best fit with the observed delta C-13 values of sedimentary n-alkanes were either hyperbolic functions or a combination of hyperbolic and sine-squared functions. Such non-linear models may be used to convert delta C-13 measurements on sedimentary n-alkanes directly into reconstructions of C-3 vegetation cover. (C) 2014 Elsevier Ltd. All rights reserved.
Current evidence suggests that all of the major events in hominin evolution have occurred in East Africa. Over the last two decades, there has been intensive work undertaken to understand African palaeoclimate and tectonics in order to put together a coherent picture of how the environment of East Africa has varied in the past. The landscape of East Africa has altered dramatically over the last 10 million years. It has changed from a relatively flat, homogenous region covered with mixed tropical forest, to a varied and heterogeneous environment, with mountains over 4 km high and vegetation ranging from desert to cloud forest. The progressive rifting of East Africa has also generated numerous lake basins, which are highly sensitive to changes in the local precipitation-evaporation regime. There is now evidence that the presence of precession-driven, ephemeral deep-water lakes in East Africa were concurrent with major events in hominin evolution. It seems the unusual geology and climate of East Africa created periods of highly variable local climate, which, it has been suggested could have driven hominin speciation, encephalisation and dispersal out of Africa. One example is the significant hominin speciation and brain expansion event at -1.8 Ma that seems to have been coeval with the occurrence of highly variable, extensive, deep-water lakes. This complex, climatically very variable setting inspired first the variability selection hypothesis, which was then the basis for the pulsed climate variability hypothesis. The newer of the two suggests that the long-term drying trend in East Africa was punctuated by episodes of short, alternating periods of extreme humidity and aridity. Both hypotheses, together with other key theories of climate-evolution linkages, are discussed in this paper. Though useful the actual evolution mechanisms, which led to early hominins are still unclear and continue to be debated. However, it is clear that an understanding of East African lakes and their palaeoclimate history is required to understand the context within which humans evolved and eventually left East Africa. (C) 2014 The Authors. Published by Elsevier Ltd.
This study examines the course and driving forces of recent vegetation change in the Mongolian steppe. A sediment core covering the last 55years from a small closed-basin lake in central Mongolia was analyzed for its multi-proxy record at annual resolution. Pollen analysis shows that highest abundances of planted Poaceae and highest vegetation diversity occurred during 1977-1992, reflecting agricultural development in the lake area. A decrease in diversity and an increase in Artemisia abundance after 1992 indicate enhanced vegetation degradation in recent times, most probably because of overgrazing and farmland abandonment. Human impact is the main factor for the vegetation degradation within the past decades as revealed by a series of redundancy analyses, while climate change and soil erosion play subordinate roles. High Pediastrum (a green algae) influx, high atomic total organic carbon/total nitrogen (TOC/TN) ratios, abundant coarse detrital grains, and the decrease of C-13(org) and N-15 since about 1977 but particularly after 1992 indicate that abundant terrestrial organic matter and nutrients were transported into the lake and caused lake eutrophication, presumably because of intensified land use. Thus, we infer that the transition to a market economy in Mongolia since the early 1990s not only caused dramatic vegetation degradation but also affected the lake ecosystem through anthropogenic changes in the catchment area.
After more than a decade of multidisciplinary studies of the Central American subduction zone mainly in the framework of two large research programmes, the US MARGINS program and the German Collaborative Research Center SFB 574, we here review and interpret the data pertinent to quantify the cycling of mineral-bound volatiles (H2O, CO2, Cl, S) through this subduction system. For input-flux calculations, we divide the Middle America Trench into four segments differing in convergence rate and slab lithological profiles, use the latest evidence for mantle serpentinization of the Cocos slab approaching the trench, and for the first time explicitly include subduction erosion of forearc basement. Resulting input fluxes are 40-62 (53) Tg/Ma/m H2O, 7.8-11.4 (9.3) Tg/Ma/m CO2, 1.3-1.9 (1.6) Tg/Ma/m Cl, and 1.3-2.1 (1.6) Tg/Ma/m S (bracketed are mean values for entire trench length). Output by cold seeps on the forearc amounts to 0.625-1.25 Tg/Ma/m H2O partly derived from the slab sediments as determined by geochemical analyses of fluids and carbonates. The major volatile output occurs at the Central American volcanic arc that is divided into ten arc segments by dextral strike-slip tectonics. Based on volcanic edifice and widespread tephra volumes as well as calculated parental magma masses needed to form observed evolved compositions, we determine long-term (10(5) years) average magma and K2O fluxes for each of the ten segments as 32-242 (106) Tg/Ma/m magma and 0.28-2.91 (1.38) Tg/Ma/m K2O (bracketed are mean values for entire Central American volcanic arc length). Volatile/K2O concentration ratios derived from melt inclusion analyses and petrologic modelling then allow to calculate volatile fluxes as 1.02-14.3 (6.2) Tg/Ma/m H2O, 0.02-0.45 (0.17) Tg/Ma/m CO2, and 0.07-0.34 (0.22) Tg/Ma/m Cl. The same approach yields long-term sulfur fluxes of 0.12-1.08 (0.54) Tg/Ma/m while present-day open-vent SO2-flux monitoring yields 0.06-2.37 (0.83) Tg/Ma/m S. Input-output comparisons show that the arc water fluxes only account for up to 40 % of the input even if we include an "invisible" plutonic component constrained by crustal growth. With 20-30 % of the H2O input transferred into the deeper mantle as suggested by petrologic modeling, there remains a deficiency of, say, 30-40 % in the water budget. At least some of this water is transferred into two upper-plate regions of low seismic velocity and electrical resistivity whose sizes vary along arc: one region widely envelopes the melt ascent paths from slab top to arc and the other extends obliquely from the slab below the forearc to below the arc. Whether these reservoirs are transient or steady remains unknown.
Response spectra are of fundamental importance in earthquake engineering and represent a standard measure in seismic design for the assessment of structural performance. However, unlike Fourier spectral amplitudes, the relationship of response spectral amplitudes to seismological source, path, and site characteristics is not immediately obvious and might even be considered counterintuitive for high oscillator frequencies. The understanding of this relationship is nevertheless important for seismic-hazard analysis. The purpose of the present study is to comprehensively characterize the variation of response spectral amplitudes due to perturbations of the causative seismological parameters. This is done by calculating the absolute parameter sensitivities (sensitivity coefficients) defined as the partial derivatives of the model output with respect to its input parameters. To derive sensitivities, we apply algorithmic differentiation (AD). This powerful approach is extensively used for sensitivity analysis of complex models in meteorology or aerodynamics. To the best of our knowledge, AD has not been explored yet in the seismic-hazard context. Within the present study, AD was successfully implemented for a proven and extensively applied simulation program for response spectra (Stochastic Method SIMulation [SMSIM]) using the TAPENADE AD tool. We assess the effects and importance of input parameter perturbations on the shape of response spectra for different regional stochastic models in a quantitative way. Additionally, we perform sensitivity analysis regarding adjustment issues of groundmotion prediction equations.
Shallow inland water bodies in Malawi continue to be threatened by various environmental challenges despite their importance to the fisheries industry. Due to the complex interaction between natural and anthropogenic disturbances, disentangling the effect of the two may be a complicated process. The littoral zone of most water bodies is important in environmental reconstructions including pollution and lake level monitoring. This study used a littoral zone, transect-based approach employing multi-proxy palaeolimnological techniques to reconstruct recent environmental change (ca. 100 yrs.) in Lake Malombe in the Malawi Rift, East Africa. The results of the study could inform fisheries management in Lake Malombe, which experienced a catastrophic decline in fish stocks. Results support documentary evidence for the complete desiccation of the lake less than 100 years ago. Subsequently, there is evidence for accelerated eutrophication in the recent past. In light of these results, it is concluded that transect sampling approaches rather than relying on single core measurements, and the need for careful consideration of the types of proxy, are significant considerations in palaeoenvironmental reconstructions.
Ostracod shells from the archaeological site Gesher BenotYa'aqov (GBY) in the upper Jordan River Valley (Israel) were investigated to improve the understanding of the environmental conditions of the Acheulian occupation site during the early-mid Pleistocene transition (0.78 Ma). The diverse ostracod assemblage consists of 28 species. The distribution of most of the recorded species in the region today shows that the hydrological conditions at the early-mid Pleistocene transition were not fundamentally different from the modern ones. However, the predominance of Candona neglecta shells in the GBY sequence probably indicates cooler climatic conditions than today. Shells of Candona angulata in the artefact-richer upper half of the sequence suggest a slight salinity increase in the ancient Hula Lake from pure freshwater to slightly oligohaline conditions. This shift probably resulted from wetter conditions and a more stable lake environment with increased residence time of the lake water and stronger influence of evaporation. Shells of the brackish water ostracod Cyprideis torosa and the slightly halophilic Heterocypris sauna and Plesiocypridopsis newtoni were recorded only rarely suggesting that the lake maintained an outlet through the entire period represented by the GBY sequence. Shells of Gomphocythere ortali in GBY cycles 1 and 2 imply that a permanent freshwater stream existed close to the site. Humphcypris subterranea shells in cycles 3-5 provide further evidence that a tributary entered the lake from the south in contrast to the modern setting with the north-south flowing Jordan River at GBY. Statistical analysis of the quantitative ostracod data from GBY identified a group of samples from layers containing more abundant stone artefacts and another group of samples from layers with scarce artefacts. Samples from layers containing more abundant artefacts have relatively high abundances of C. angulata, Darwinula stevensoni and Physocypria kraepelini shells and include rare shells of Ilyocypris hartmanni, Ilyocypris salebrosa, Heterocypris incongniens and Pseudocandona sp. 2 which do not occur in the other samples. The presence of P. kraepelini and H. incongruens shells in artefact-richer sediments possibly indicates poor bottom water oxygenation in the ancient Hula lake sometimes during the periods of Acheulian occupation. However, more detailed studies are required to assess whether lower dissolved oxygen levels in the lake resulted from a slight lake level rise and possibly higher nutrient flux to the lake during wetter conditions or whether hominins already impacted lake's nutrient status by butchering at its shore or by burning of near-shore vegetation. (c) 2014 Elsevier B.V. All rights reserved.
We isolated and characterized 16 new di- and tetranudeotide microsatellite markers for the critically endangered Asian box turtle genus Cuora, focusing on the "Cuora trifasciata" species complex. The new markers were then used to analyse genetic variability and divergence amongst five described species within this complex, namely C. aurocapitata (n = 18), C. cyclornata (n = 31), C. pani (n = 6), C. trifasciata (n = 58), and C. zhoui (n = 7). Our results support the view that all five species represent valid taxa. Within two species (C. trifasciata and C. cyclornata), two distinct morphotypes were corroborated by microsatellite divergence. For three individuals, morphologically identified as being of hybrid origin, the hybrid status was confirmed by our genetic analysis. Our results confirm the controversial species (Cuora aurocapitata, C. cyclornata) and subspecies/morphotypes (C. cyclornata meieri, C. trifasciata cf. trifasciata) to be genetically distinct, which has critical implications for conservation strategies.
Sediment-discharge hysteresis loops are frequently analyzed to facilitate the understanding of sediment transport processes. Hysteresis patterns, however, are often complex and their interpretation can be complicated. Particularly, quantifying hysteresis patterns remains a problematic issue. Moreover, it is currently unknown how much data is required for analyzing sediment-discharge hysteresis loops in a given area. These open questions and challenges motivated us to develop a new method for quantifying suspended-sediment hysteresis. Subsequently, we applied the new hysteresis index to three suspended-sediment and discharge datasets from a small tropical rainforest catchment. The datasets comprised a different number of events and sampling sites. Our analyses show three main findings: (1) datasets restricted to only few events, which is typical for rapid assessment surveys, were always sufficient to identify the dominating hysteresis pattern in our research area. Furthermore, some of these small datasets contained multiple-peak events that allowed identifying intra-event exhaustion effects and hence, limitations in sediment supply. (2) Datasets comprising complete hydrological years were particularly useful for analyzing seasonal dynamics of hysteresis. These analyses revealed an exhaustion of hysteresis on the inter-event scale which also points to a limited sediment supply. (3) Datasets comprising measurements from two consecutive gauges installed at the catchment outlet and on a slope within that catchment allowed analyzing the change of hysteresis patterns along the flowpath. On the slope, multiple-peak events showed a stronger intra-event exhaustion of hysteresis than at the catchment outlet. Furthermore, exhaustion of hysteresis on the inter-event scale was not evident on the slope but occurred at the catchment outlet. Our results indicate that even small sediment datasets can provide valuable insights into sediment transport processes of small catchments. Furthermore, our results may serve as a first guideline on what to expect from an analysis of hysteresis patterns for datasets of varying quality and quantity. (c) 2014 Elsevier B.V. All rights reserved.
Military areas are valuable habitats and refuges for rare and endangered plants and animals. We developed a new approach applying innovative methods of hyperspectral remote sensing to bridge the existing gap between remote sensing technology and the demands of the nature conservation community. Remote sensing has already proven to be a valuable monitoring instrument. However, the approaches lack the consideration of the demands of applied nature conservation which includes the legal demands of the EU Habitat Directive. Following the idea of the Vital Signs Monitoring in the USA, we identified a subset of the highest priority monitoring indicators for our study area. We analyzed continuous spectral response curves and tested the measurability of N=19 indicators on the basis of complexity levels aggregated from extensive vegetation assemblages. The spectral differentiability for the floristic as well as faunistic indicators revealed values up to 100% accuracy. We point out difficulties when it comes to distinguishing faunistic habitat requirements of several species adapted to dry open landscapes, which in this case results in OVERALL ACCURACY of 67, 87-95, and 35% in the error matrix. In summary, we provide an applicable and feasible method to facilitating monitoring military areas by hyperspectral remote sensing in the following. (C) 2014 Elsevier Ltd. All rights reserved.
We track a bilateral rupture propagation lasting similar to 160 s, with its dominant branch rupturing northeastwards at about 3 kms(-1). The area of maximum energy emission is offset from the maximum coseismic slip but matches the zone where most plate interface aftershocks occur. Along dip, energy is preferentially released from two disconnected interface belts, and a distinct jump from the shallower belt to the deeper one is visible after about 20 s from the onset. However, both belts keep on being active until the end of the rupture. These belts approximately match the position of the interface aftershocks, which are split into two clusters of events at different depths, thus suggesting the existence of a repeated transition from stick-slip to creeping frictional regime.
We focus on the relation between seismic and total postseismic afterslip following the Maule M-w 8.8 earthquake on 2010 February 27 in central Chile. First, we calculate the cumulative slip released by aftershock seismicity. We do this by summing up the aftershock regions and slip estimated from scaling relations. Comparing the cumulative seismic slip with afterslip modelswe showthat seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints. As the afterslip model implicitly contains the displacements from the aftershocks, this reflects the tendency of afterslip models to smear out the actual slip pattern. However, it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor. This effect, seen weakly for the Maule 2010 and also for the Tohoku 2011 earthquake, can be explained by taking into account the uncertainties of the seismicity and afterslip models. In spite of uncertainties, the hypocentral region of the Nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically. Therefore, these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture. In a second step, we divide the megathrust of the Maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time. We then compare this number to a time-dependent afterslip model by defining the 'afterslip to aftershock ratio' (ASAR) for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count. Although we find a linear relation between afterslip and aftershocks for most cells, there is significant variability in ASAR in both the downdip and along-strike directions of the megathrust. We compare the spatial distribution of ASAR with the spatial distribution of seismic coupling, coseismic slip and Bouguer gravity anomaly, and in each case we find no significant correlation.
The Indus River, one of Asia's premier rivers, drains the western Tibetan Plateau and the Nanga Parbat syntaxis. These two areas juxtapose some of the lowest and highest topographic relief and commensurate denudation rates in the Himalaya-Tibet orogen, respectively, yet the spatial pattern of denudation rates upstream of the syntaxis remains largely unclear, as does the way in which major rivers drive headward incision into the Tibetan Plateau. We report a new inventory of Be-10-based basinwide denudation rates from 33 tributaries flanking the Indus River along a 320 km reach across the western Tibetan Plateau margin. We find that denudation rates of up to 110 mm k.y.(-1) in the Ladakh and Zanskar Ranges systematically decrease eastward to 10 mm k.y.(-1) toward the Tibetan Plateau. Independent results from bulk petrographic and heavy mineral analyses support this denudation gradient. Assuming that incision along the Indus exerts the base-level control on tributary denudation rates, our data show a systematic eastward decrease of landscape downwearing, reaching its minimum on the Tibetan Plateau. In contrast, denudation rates increase rapidly 150-200 km downstream of a distinct knick-point that marks the Tibetan Plateau margin in the Indus River longitudinal profile. We infer that any vigorous headward incision and any accompanying erosional waves into the interior of the plateau mostly concerned reaches well below this plateau margin. Moreover, reported long-term (>10(6) yr) exhumation rates from low-temperature chronometry of 0.1-0.75 mm yr(-1) consistently exceed our Be-10-derived denudation rates. With averaging time scales of 10(3)-10(4) yr for our denudation data, we report postglacial rates of downwearing in a tectonically idle landscape. To counterbalance this apparent mismatch, denudation rates must have been higher in the Quaternary during glacial-interglacial intervals.
Submerged macrophytes can stabilise clear water conditions in shallow lakes. However, many existing models for deep lakes neglect their impact. Here, we tested the hypothesis that submerged macrophytes can affect the water clarity in deep lakes. A one-dimensional, vertically resolved macrophyte model was developed based on PCLake and coupled to SALMO-1D and GOTM hydrophysics and validated against field data. Validation showed good coherence in dynamic growth patterns and colonisation depths. In our simulations the presence of submerged macrophytes resulted in up to 50% less phytoplankton biomass in the shallowest simulated lake (11 m) and still 15% less phytoplankton was predicted in 100 m deep oligotrophic lakes. Nutrient loading, lake depth, and lake shape had a strong influence on macrophyte effects. Nutrient competition was found to be the strongest biological interaction. Despite a number of limitations, the derived dynamic lake model suggests significant effects of submerged macrophytes on deep lake water quality. (C) 2014 Elsevier Ltd. All rights reserved.
The hydrology of western Central Asia is highly sensitive to climatic perturbations. In order to understand its long-term variability and to infer linkages between precipitation and atmospheric and oceanic systems, we conducted a thorough sedimentary and geochemical study on a composite core retrieved in lake Son Kul (central Kyrgyzstan). A multi-proxy approach was conducted on lake sediments based on grain size analyses, magnetic susceptibility, total organic carbon (TOC), total nitrogen (TN) and carbon and oxygen isotope analyses on bulk and biogenic materials (ostracoda and molluscs shells) at a resolution equivalent to ca 40 years, aiming to characterise the sequence of palaeolimnological changes in Son Kul.
As indicated by delta O-18 record of bulk carbonates, mainly consisting of aragonite, the Holocene hydrological balance was negative during most of time, suggesting an excess of evaporation (E) over precipitation (P). Limnological conditions fluctuated rapidly before 5000 cal yr BP indicating significant changes in regional hydrology and climate. In particular, the long-term negative hydrological balance was impeded by several short stages with marked increase of precipitation, lasting several decades to a few centuries (e.g., 8300-8200, 6900-6700, 6300-6100, 5500-5400, 5300-5200 and 3100 -3000 cal yr BP). Precipitation changes as inferred from 8180 data are also documented by increased minerogenic detritus and higher TOC. We propose that the seasonal pattern of precipitation varied transiently in western Central Asia during the Holocene, although evaporation changes may also account for the rapid changes observed in delta O-18 data. When the annual water balance was less critical (P <= E), the excess of water might be ascribed to increased precipitation during cold seasons mainly because winter precipitation has more negative delta O-18 than its summer equivalent. Conversely, when the annual water balance is negative (P E), the moisture was mainly delivered during the warm season, as between 5000 and 2000 cal yr BP. Our results thus imply that moisture sources could have changed as well during the Holocene. Moisture was delivered as today mainly during summer from the extended Caspian-Aral Basin and eastern Mediterranean, although Arctic and even North Atlantic seas might be important moisture sources when seasonal precipitation was dominated by winter precipitation. We hypothesise that warming Arctic and North Atlantic seas were important for the North Hemisphere circulation during the cold season. (C) 2014 Elsevier Ltd. All rights reserved.
The real-time recognition and precise correction of baseline shifts in strong-motion records is a critical issue for GPS and accelerometer combined processing. This paper proposes a method to adaptively recognize and correct baseline shifts in strong-motion records by utilizing GPS measurements using two phases Kalman filter. By defining four kinds of learning statistics and criteria, the time series of estimated baseline shifts can be divided into four time intervals: initialization, static, transient and permanent. During the time interval in which the transient baseline shift is recognized, the dynamic noise of the Kalman filter system and the length of the baseline shifts estimation window are adaptively adjusted to yield a robust integration solution. The validations from an experimental and real datasets show that acceleration baseline shifts can be precisely recognized and corrected, thus, the combined system adaptively adjusted the estimation strategy to get a more robust solution. (C) 2014 COSPAR. Published by Elsevier Ltd. All rights reserved.
Oxygen isotope compositions are reported for the first time for the Himalayan metabasites of the Kaghan Valley, Pakistan in this study. The highest metamorphic grades are recorded in the north of the valley, near the India-Asia collision boundary, in the form of high-pressure (HP: Group I) and ultrahigh-pressure (UHP: Group II) eclogites. The rocks show a step-wise decrease in grade from the UHP to HP eclogites and amphibolites. The protoliths of these metabasites were the Permian Panjal Trap basalts (ca. 267 +/- 2.4 Ma), which were emplaced along the northern margin of India when it was part of Gondwana. After the break-up of Gondwana, India drifted northward, subducted beneath Asia and underwent UHP metamorphism during the Eocene (ca. 45 +/- 1.2 Ma). At the regional scale, amphibolites, Group I and II eclogites yielded delta O-18 values of +5.84 and +5.91 parts per thousand, +1.66 to +424 parts per thousand, and -2.25 to +0.76 parts per thousand, respectively, relative to VSMOW. On a more local scale, within a single eclogite body, the delta O-18 values were the lowest (-2.25 to-1.44%.) in the central, the best preserved (least retrograded) parts, and show a systematic increase outward into more retrograded rocks, reaching up to +0.12 parts per thousand. These values are significantly lower than the typical mantle values for basalts of + 5.7 +/- 0.3 parts per thousand. The unusually low or negative delta O-18 values in Group II eclogites potentially resulted from hydrothermal alteration of the protoliths by interactions with meteoric water when the Indian plate was at southern high latitudes (similar to 60 degrees S). The stepwise increase in delta O-18 values, among different eclogite bodies in general and at single outcrop-scales in particular, reflects differing degrees of resetting of the oxygen isotope compositions during exhumation-related retrogression. (C) 2014 Elsevier B.V. All rights reserved.
Quantitative geochemical modeling is today applied in a variety of geological environments from the petrogenesis of igneous rocks to radioactive waste disposal. In addition, the development of thermodynamic databases and computer programs to calculate equilibrium phase diagrams has greatly advanced our ability to model geodynamic processes. Combined with experimental data on elemental partitioning and isotopic fractionation, thermodynamic forward modeling unfolds enormous capacities that are far from exhausted.
In metamorphic petrology the combination of thermodynamic and trace element forward modeling can be used to study and to quantify processes at spatial scales from mu m to km. The thermodynamic forward models utilize Gibbs energy minimization to quantify mineralogical changes along a reaction path of a chemically open fluid/rock system. These results are combined with mass balanced trace element calculations to determine the trace element distribution between rock and melt/fluid during the metamorphic evolution. Thus, effects of mineral reactions, fluid-rock interaction and element transport in metamorphic rocks on the trace element and isotopic composition of minerals, rocks and percolating fluids or melts can be predicted.
Here we illustrate the capacities of combined thermodynamic-geochemical modeling based on two examples relevant to mass transfer during metamorphism. The first example focuses on fluid-rock interaction in and around a blueschist-facies shear zone in felsic gneisses, where fluid-induced mineral reactions and their effects on boron (B) concentrations and isotopic compositions in white mica are modeled. In the second example, fluid release from a subducted slab, the associated transport of B as well as variations in B concentrations and isotopic compositions in liberated fluids and residual rocks are modeled. We compare the modeled results of both examples to geochemical data of natural minerals and rocks and demonstrate that the combination of thermodynamic and geochemical models enables quantification of metamorphic processes and insights into element cycling that would have been unattainable if only one model approach was chosen. (C) 2014 Elsevier B.V. All rights reserved.
The Indian Monsoon Variability during the past Millennium has been simulated with the ECHAM5 model in two different time slices: Medieval Climate Anomaly and the Little Ice Age. The simulations are compared with new centennial-resolving paleo-reconstructions inferred from various well-dated multi-proxies from two core regions, the Himalaya and Central India. A qualitative moisture index is derived from the proxies and compared with simulated moisture anomalies.
The reconstructed paleo-hydrological changes between the Little Ice Age and the Medieval Climate Anomaly depict a dipole pattern between Himalaya and Central India, which is also captured by the model.
In the Medieval Climate Anomaly the model exhibits stronger (weaker) dipole signals during summer (winter) compared to Little Ice Age. In summer (winter) months of "Medieval Climate Anomaly minus Little Ice Age" the model simulates wetter conditions over eastern (western and central) Himalaya. Over Central India, a simulated weakening of Indian Summer Monsoon during warmer climate is coincident with reconstructed drying signal in the Lonar Lake record.
Based on the model simulations, we can differentiate three physical mechanisms which can lead to the moisture anomalies: (i) the western and central Himalaya are influenced by extra-tropical Westerlies during winter, (ii) the eastern Himalaya is affected by summer variations of temperature gradient between Bay of Bengal and Indian subcontinent and by a zonal band of intensified Indian-East Asian monsoon link north of 25 degrees N, and (iii) Central India is dominated by summer sea surface temperature anomalies in the northern Arabian Sea which have an effect on the large-scale advection of moist air masses. The temperatures in the Arabian Sea are linked to the Ind Pacific Warm Pool, which modulates the Indian monsoon strength. (C) 2014 The Authors. Published by Elsevier B.V.
Dealing with predicted increases in extreme weather conditions due to climate change requires robust knowledge about controls on rainfall-triggered landslides. We explore relationships between rainfall and landslide size throughout the Japanese archipelago. We test whether the total volume of landslides can be predicted directly from rainfall totals, intensity, and duration using a nationwide inventory of 4744 rainfall-triggered landslides recorded from A.D. 2001 to 2011. We find that larger landslides were more abundant at the expense of smaller ones when total, maximum, and mean rainfall intensity exceeded similar to 250 mm, similar to 35 mm/h, and similar to 4 mm/h, respectively. Frequency distributions of these rainfall parameters are peaked and heavily skewed. Yet neither the most frequent nor the most extreme values of these rainfall metrics coincide consistently with the maximum landslide volumes. A striking decrease of landslide volumes at both mean and maximum rainfall intensity, as well as duration, points to an exhaustion in hillslope geomorphic response regardless of sample size, landslide type, mobilized volume, dominant lithology, or reporting bias. Our results underscore substantial offsets between the peaks of rainfall metrics and maximum associated landslide volumes, thus complicating straightforward estimates of geomorphic work from metrics of rainstorm magnitude or frequency. Only the rainfall total appears to be a suitable monotonic predictor of landslide volumes mobilized during typhoons and frontal storms.
Integrated biostratigraphic-chemostratigraphic studies provide evidence that the proto-North Atlantic realm witnessed major changes in carbonate platform production in the run-up of the Early Aptian oceanic anoxic event (OAE) 1a. Whereas pervasive growth of Lithocodium microencrusters represents an early harbinger of OAE1a-related environmental perturbation, the subsequent replacement of oligotrophic rudist-coral-nerineid by mesotrophic orbitolinid-oyster communities was clearly associated with the event itself. In order to test the supra-regional relevance of this major community replacement, two shallow-water sections in the southern Lusitanian Basin (Portugal) are investigated by means of geochemistry (carbon and oxygen isotopes), cement petrography and detailed sedimentological analysis. The focus is on a regional, prominent discontinuity surface (S4) at the transition between oligotrophic and mesotrophic carbonate platform production, which might indicate that the major biotic change could have been associated with a phase of non-sedimentation and possibly erosion. The studied sections (Sao Julia, Crismina) provide evidence that the major Early Aptian biotic turnover was preceded by numerous subordinate but significant changes in platform ecology, which mirrored a series of progressive short-term environmental changes in the course of OAE1. Several transient mass occurrences of orbitolinids indicate repeated phases of ecological stress arguably due to enhanced nutrient input and deepening. Small-scale sea-level changes at parasequence level below the major discontinuity surface are revealed by alternations of rudist assemblages dominated by clinger or recumbent forms as well as intercalated hardground and subaerial exposure stages. Expanded phases of subaerial exposure, however, can be largely ruled out following the geochemical and cement-petrographic data presented here. Enhanced continent-derived siliciclastic input characterising the lower orbitolinid-oyster dominated limestones is in support of a shift to more humid conditions during the middle Early Aptian. This is in line with palaeoclimatic data, which propose a southward movement of the mid-latitude arid climate belt during this time. The documented rapid replacement of oligotrophic assemblages by various environmental-stress adapted carbonate platform communities might be seen as explanation for ongoing Early Aptian proto-North Atlantic carbonate production during a time of widespread platform demise and drowning in the northern Tethyan realm. (C) 2014 Elsevier B.V. All rights reserved.
The literature on the costing of mitigation measures for reducing impacts of natural hazards is rather fragmented. This paper provides a concise overview of the current state of knowledge in Europe on the costing of mitigation measures for the reduction of natural hazard risks (droughts, floods, storms and induced coastal hazards as well as alpine hazards) and identifies knowledge gaps and related research recommendations. Furthermore, it provides a taxonomy of related mitigation options, classifying them into nine categories: (1) management plans, land-use planning, and climate adaptation; (2) hazard modification; (3) infrastructure; (4) mitigation measures (stricto sensu); (5) communication in advance of events; (6) monitoring and early warning systems; (7) emergency response and evacuation; (8) financial incentives; and (9) risk transfer (including insurance). It is found that the costing of mitigation measures in European and in other countries has almost exclusively focused on estimating direct costs. A cost assessment framework that addresses a range of costs, possibly informed by multiple stakeholders, would provide more accurate estimates and could provide better guidance to decision makers. (C) 2014 American Society of Civil Engineers.
We used inverse modelling techniques and soil moisture measured by the cosmic-ray neutron sensing (CRS) to estimate root-zone soil hydraulic properties at the field scale. A HYDRUS-1D model was developed for inverse modelling and calibrated with parameter estimation software (PEST) using a global optimizer. Integral CRS measurements recorded from a sunflower farm in Germany comprised the model input. Data were transformed to soil water storage to enable direct model calibration with a HYDRUS soil-water balance. Effective properties at the CRS scale were compared against local measurements and other inversely estimated soil properties from independent soil moisture profiles. Moreover, CRS-scale soil properties were tested on the basis of how field soil moisture (vertical distribution) and soil water storage were reproduced. This framework provided good estimates of effective soil properties at the CRS scale. Simulated soil moisture at different depths at the CRS scale agreed with field observations. Moreover, simulated soil water storage at the CRS scale compared well with calculations from point-scale profiles, despite their different support volumes. The CRS-scale soil properties estimated with the inverse model were within the range of variation of properties identified from all inverse simulations at the local scale. This study demonstrates the potential of CRS for inverse estimation of soil hydraulic properties.
Soil in a changing world is subject to both anthropogenic and environmental stresses. Soil monitoring is essential to assess the magnitude of changes in soil variables and how they affect ecosystem processes and human livelihoods. However, we cannot always be sure which sampling design is best for a given monitoring task. We employed a rotational stratified simple random sampling (rotStRS) for the estimation of temporal changes in the spatial mean of saturated hydraulic conductivity (K-s) at three sites in central Panama in 2009, 2010 and 2011. To assess this design's efficiency we compared the resulting estimates of the spatial mean and variance for 2009 with those gained from stratified simple random sampling (StRS), which was effectively the data obtained on the first sampling time, and with an equivalent unexecuted simple random sampling (SRS). The poor performance of geometrical stratification and the weak predictive relationship between measurements of successive years yielded no advantage of sampling designs more complex than SRS. The failure of stratification may be attributed to the small large-scale variability of K-s. Revisiting previously sampled locations was not beneficial because of the large small-scale variability in combination with destructive sampling, resulting in poor consistency between revisited samples. We conclude that for our K-s monitoring scheme, repeated SRS is equally effective as rotStRS. Some problems of small-scale variability might be overcome by collecting several samples at close range to reduce the effect of small-scale variation. Finally, we give recommendations on the key factors to consider when deciding whether to use stratification and rotation in a soil monitoring scheme.
We assessed tropical montane cloud forest (TMCF) sensitivity to natural disturbance by drought, fire, and dieback with a 7300-year-long paleorecord. We analyzed pollen assemblages, charcoal accumulation rates, and higher plant biomarker compounds (average chain length [ACL] of n-alkanes) in sediments from Wai 'anapanapa, a small lake near the upper forest limit and the mean trade wind inversion ('IWI) in Hawai`i. The paleorecord of ACL suggests increased drought frequency and a lower awl elevation from 2555-1323 cal yr B.P. and 606-334 cal yr B.P. Charcoal began to accumulate and a novel fire regime was initiated ca. 880 cal yr B.P., followed by a decreased fire return interval at ca. 550 cal yr B.P. Diebacks occurred at 2931, 2161, 1162, and 306 cal yr B.P., and two of these were independent of drought or fire. Pollen assemblages indicate that on average species composition changed only 2.8% per decade. These dynamics, though slight, were significantly associated with disturbance. The direction of species composition change varied with disturbance type. Drought was associated with significantly more vines and lianas; fire was associated with an increase in the tree fern Sadleria and indicators of open, disturbed landscapes at the expense of epiphytic ferns; whereas stand-scale dieback was associated with an increase in the tree fern Cibotium. Though this cloud forest was dynamic in response to past disturbance, it has recovered, suggesting a resilient TMCF with no evidence of state change in vegetation type (e.g., grassland or shrubland).
The spatiotemporal, kinematic, and source characteristics of induced seismicity occurring at different fluid injection rates are investigated to determine the predominant physical mechanisms responsible for induced seismicity at the northwestern part of The Geysers geothermal field, California. We analyze a relocated hypocenter catalog from a seismicity cluster where significant variations of the stress tensor orientation were previously observed to correlate with injection rates. We find that these stress tensor orientation changes may be related to increased pore pressure and the corresponding changes in poroelastic stresses at reservoir depth. Seismic events during peak injections tend to occur at greater distances from the injection well, preferentially trending parallel to the maximum horizontal stress direction. In contrast, at lower injection rates the seismicity tends to align in a different direction which suggests the presence of a local fault. During peak injection intervals, the relative contribution of strike-slip faulting mechanisms increases. Furthermore, increases in fluid injection rates also coincide with a decrease in b values. Our observations suggest that regardless of the injection stage, most of the induced seismicity results from thermal fracturing of the reservoir rock. However, during peak injection intervals, the increase in pore pressure may likewise be responsible for the induced seismicity. By estimating the thermal and hydraulic diffusivities of the reservoir, we confirm that the characteristic diffusion length for pore pressure is much greater than the corresponding length scale for temperature and also more consistent with the spatial extent of seismicity observed during different injection rates.
Recultivation of disturbed oil sand mining areas is an issue of increasing importance. Nevertheless only little is known about the fate of organic matter, cell abundances and microbial community structures during oil sand processing, tailings management and initial soil development on reclamation sites. Thus the focus of this work is on biogeochemical changes of mined oil sands through the entire process chain until its use as substratum for newly developing soils on reclamation sites. Therefore, oil sand, mature fine tailings (MFTs) from tailings ponds and drying cells and tailings sand covered with peat-mineral mix (PMM) as part of land reclamation were analyzed. The sample set was selected to address the question whether changes in the above-mentioned biogeochemical parameters can be related to oil sand processing or biological processes and how these changes influence microbial activities and soil development.
GC-MS analyses of oil-derived biomarkers reveal that these compounds remain unaffected by oil sand processing and biological activity. In contrast, changes in polycyclic aromatic hydrocarbon (PAH) abundance and pattern can be observed along the process chain. Especially naphthalenes, phenanthrenes and chrysenes are altered or absent on reclamation sites, Furthermore, root-bearing horizons on reclamation sites exhibit cell abundances at least ten times higher (10(8) to 10(9) cells g(-1)) than in oil sand and MFF samples (10(7) cells g(-1)) and show a higher diversity in their microbial community structure. Nitrate in the pore water and roots derived from the PMM seem to be the most important stimulants for microbial growth. The combined data show that the observed compositional changes are mostly related to biological activity and the addition of exogenous organic components (PMM), whereas oil extraction, tailings dewatering and compaction do not have significant influences on the evaluated compounds. Microbial community composition remains relatively stable through the entire process chain. (C) 2014 Elsevier B.V. All rights reserved.
The Himalayan mountains are dissected by some of the deepest and most impressive gorges on Earth. Constraining the interplay between river incision and rock uplift is important for understanding tectonic deformation in this region. We report here the discovery of a deeply incised canyon of the Yarlung Tsangpo River, at the eastern end of the Himalaya, which is now buried under more than 500 meters of sediments. By reconstructing the former valley bottom and dating sediments at the base of the valley fill, we show that steepening of the Tsangpo Gorge started at about 2 million to 2.5 million years ago as a consequence of an increase in rock uplift rates. The high erosion rates within the gorge are therefore a direct consequence of rapid rock uplift.
Due to increasing demands and competition for high quality groundwater resources in many parts of the world, there is an urgent need for efficient methods that shed light on the interplay between complex natural settings and anthropogenic impacts. Thus a new approach is introduced, that aims to identify and quantify the predominant processes or factors of influence that drive groundwater and lake water dynamics on a catchment scale. The approach involves a non-linear dimension reduction method called Isometric feature mapping (Isomap). This method is applied to time series of groundwater head and lake water level data from a complex geological setting in Northeastern Germany. Two factors explaining more than 95% of the observed spatial variations are identified: (1) the anthropogenic impact of a waterworks in the study area and (2) natural groundwater recharge with different degrees of dampening at the respective sites of observation. The approach enables a presumption-free assessment to be made of the existing geological conception in the catchment, leading to an extension of the conception. Previously unknown hydraulic connections between two aquifers are identified, and connections revealed between surface water bodies and groundwater. (C) 2014 Elsevier B.V. All rights reserved.
Subsurface stormflow is thought to occur mainly in humid environments with steep terrains. However, in semi-arid areas, preferential flow through macropores can also result in a significant contribution of subsurface stormflow to catchment runoff for varying catchment conditions. Most hydrological models neglect this important subsurface preferential flow. Here, we use the process-oriented hydrological model Hillflow-3D, which includes a macropore flow approach, to simulate rainfall-runoff in the semi-arid Parapunos catchment in Spain, where macropore flow was observed in previous research. The model was extended for this study to account for sorptivity under very dry soil conditions. The results of the model simulations with and without macropore flow are compared. Both model versions give reasonable results for average rainfall situations, although the approach with the macropore concept provides slightly better results. The model results for scenarios of extreme rainfall events (>13.3mm30min(-1)) however show large differences between the versions with and without macropores. These model results compared with measured rainfall-runoff data show that the model with the macropore concept is better. Our conclusion is that preferential flow is important in controlling surface runoff in case of specific, high intensity rainfall events. Therefore, preferential flow processes must be included in hydrological models where we know that preferential flow occurs. Hydrological process models with a less detailed process description may fit observed average events reasonably well but can result in erroneous predictions for more extreme events. Copyright (c) 2013 John Wiley & Sons, Ltd.
A valley-filling ignimbrite re-exposed through subsequent river incision at the southern margin of the Andean (Puna) plateau preserves pristine geological evidence of pre-late Miocene palaeotopography in the north western Argentine Andes. Our new Ar-40/(39) Ar dating of the Las Papas Ignimbrites yields a plateau age of 9.24 +/- 0.03 Ma, indicating valley-relief and orographic-barrier conditions comparable to the present-day. A later infill of Plio-Pleistocene coarse conglomerates has been linked to wetter conditions, but resulted in no additional net incision of the Las Papas valley, considering that the base of the ignimbrite remains unexposed in the valley bottom. Our observations indicate that at least 550 m of local plateau margin relief (and likely > 2 km) existed by 9 Ma at the southern Puna margin, which likely aided the efficiency of the orographic barrier to rainfall along the eastern and south eastern flanks of the Puna and causes aridity in the plateau interior.
To support scientifically sound water management in dryland environments a modelling system has been developed for the quantitative assessment of water and sediment fluxes in catchments, transport in the river system, and retention in reservoirs. The spatial scale of interest is the mesoscale because this is the scale most relevant for management of water and land resources.
This modelling system comprises process-oriented hydrological components tailored for dryland characteristics coupled with components comprising hillslope erosion, sediment transport and reservoir deposition processes. The spatial discretization is hierarchically designed according to a multi-scale concept to account for particular relevant process scales. The non-linear and partly intermittent run-off generation and sediment dynamics are dealt with by accounting for connectivity phenomena at the intersections of landscape compartments. The modelling system has been developed by means of data from nested research catchments in NE-Spain and in NE-Brazil.
In the semi-arid NE of Brazil sediment retention along the topography is the main process for sediment retention at all scales, i.e. the sediment delivery is transport limited. This kind of deposition retains roughly 50 to 60 % of eroded sediment, maintaining a similar deposition proportion in all spatial scales investigated. On the other hand, the sediment retained in reservoirs is clearly related to the scale, increasing with catchment area. With increasing area, there are more reservoirs, increasing the possibility of deposition. Furthermore, the area increase also promotes an increase in flow volume, favouring the construction of larger reservoirs, which generally overflow less frequently and retain higher sediment fractions. The second example comprises a highly dynamic Mediterranean catchment in NE-Spain with nested sub-catchments and reveals the full dynamics of hydrological, erosion and deposition features. The run-off modelling performed well with only some overestimation during low-flow periods due to the neglect of water losses along the river. The simulated peaks in sediment flux are reproduced well, while low-flow sediment transport is less well captured, due to the disregard of sediment remobilization in the riverbed during low flow.
This combined observation and modelling study deepened the understanding of hydro-sedimentological systems characterized by flashy run-off generation and by erosion and sediment transport pulses through the different landscape compartments. The connectivity between the different landscape compartments plays a very relevant role, regarding both the total mass of water and sediment transport and the transport time through the catchment.
Many Mediterranean drylands are characterized by strong erosion in headwater catchments, where connectivity processes play an important role in the redistribution of water and sediments. Sediment connectivity describes the ease with which sediment can move through a catchment. The spatial and temporal characterization of connectivity patterns in a catchment enables the estimation of sediment contribution and transfer paths. Apart from topography, vegetation cover is one of the main factors driving sediment connectivity. This is particularly true for the patchy vegetation cover typical of many dryland environments. Several connectivity measures have been developed in the last few years. At the same time, advances in remote sensing have enabled an improved catchment-wide estimation of ground cover at the subpixel level using hyperspectral imagery.
The objective of this study was to assess the sediment connectivity for two adjacent subcatchments (similar to 70 km(2)) of the Isabena River in the Spanish Pyrenees in contrasting seasons using a quantitative connectivity index based on fractional vegetation cover and topography data. The fractional cover of green vegetation, non-photosynthetic vegetation, bare soil and rock were derived by applying a multiple endmember spectral mixture analysis approach to the hyperspectral image data. Sediment connectivity was mapped using the index of connectivity, in which the effect of land cover on runoff and sediment fluxes is expressed by a spatially distributed weighting factor. In this study, the cover and management factor (C factor) of the Revised Universal Soil Loss Equation (RUSLE) was used as a weighting factor. Bi-temporal C factor maps were derived by linking the spatially explicit fractional ground cover and vegetation height obtained from the airborne data to the variables of the RUSLE subfactors.
The resulting connectivity maps show that areas behave very differently with regard to connectivity, depending on the land cover and on the spatial distribution of vegetation abundances and topographic barriers. Most parts of the catchment show higher connectivity values in August as compared to April. The two subcatchments show a slightly different connectivity behaviour that reflects the different land cover proportions and their spatial configuration.
The connectivity estimation can support a better understanding of processes controlling the redistribution of water and sediments from the hillslopes to the channel network at a scale appropriate for land management. It allows hot spot areas of erosion to be identified and the effects of erosion control measures, as well as different land management scenarios, to be studied.
Knowledge of sediment sources is a prerequisite for sustainable management practices and may furthermore improve our understanding of water and sediment fluxes. Investigations have shown that a number of characteristic soil properties can be used as "fingerprints" to trace back the sources of river sediments. Spectral properties have recently been successfully used as such characteristics in fingerprinting studies. Despite being less labour-intensive than geochemical analyses, for example, spectroscopy allows measurements of small amounts of sediment material (> 60 mg), thus enabling inexpensive analyses even of intra-event variability. The focus of this study is on the examination of spectral properties of fluvial sediment samples to detect changes in source contributions, both between and within individual flood events.
Sediment samples from the following three different origins were collected in the Isabena catchment (445 km(2)) in the central Spanish Pyrenees: (1) soil samples from the main potential source areas, (2) stored fine sediment from the channel bed once each season in 2011 and (3) suspended sediment samples during four flood events in autumn 2011 and spring 2012 at the catchment outlet as well as at several subcatchment outlets. All samples were dried and measured for spectral properties in the laboratory using an ASD spectroradiometer. Colour parameters and physically based features (e.g. organic carbon, iron oxide and clay content) were calculated from the spectra. Principal component analyses (PCA) were applied to all three types of samples to determine natural clustering of samples, and a mixing model was applied to determine source contributions.
We found that fine sediment stored in the river bed seems to be mainly influenced by grain size and seasonal variability, while sampling location-and thus the effect of individual tributaries or subcatchments-seem to be of minor importance. Suspended sediment sources were found to vary between, as well as within, flood events; although badlands were always the major source. Forests and grasslands contributed little (< 10 %), and other sources (not further determinable) contributed up to 40 %. The analyses further suggested that sediment sources differ among the subcatchments and that subcatchments comprising relatively large proportions of badlands contributed most to the four flood events analyzed.
Spectral fingerprints provide a rapid and cost-efficient alternative to conventional fingerprint properties. However, a combination of spectral and conventional fingerprint properties could potentially permit discrimination of a larger number of source types.
Knowledge of the origin of suspended sediment is important for improving our understanding of sediment dynamics and thereupon support of sustainable watershed management. An direct approach to trace the origin of sediments is the fingerprinting technique. It is based on the assumption that potential sediment sources can be discriminated and that the contribution of these sources to the sediment can be determined on the basis of distinctive characteristics (fingerprints). Recent studies indicate that visible-near-infrared (VNIR) and shortwave-infrared (SWIR) reflectance characteristics of soil may be a rapid, inexpensive alternative to traditional fingerprint properties (e.g. geochemistry or mineral magnetism).
To further explore the applicability of VNIR-SWIR spectral data for sediment tracing purposes, source samples were collected in the Isabena watershed, a 445 km(2) dryland catchment in the central Spanish Pyrenees. Grab samples of the upper soil layer were collected from the main potential sediment source types along with in situ reflectance spectra. Samples were dried and sieved, and artificial mixtures of known proportions were produced for algorithm validation. Then, spectral readings of potential source and artificial mixture samples were taken in the laboratory. Colour coefficients and physically based parameters were calculated from in situ and laboratory-measured spectra. All parameters passing a number of prerequisite tests were subsequently applied in discriminant function analysis for source discrimination and mixing model analyses for source contribution assessment.
The three source types (i.e. badlands, forest/grassland and an aggregation of other sources, including agricultural land, shrubland, unpaved roads and open slopes) could be reliably identified based on spectral parameters. Laboratory-measured spectral fingerprints permitted the quantification of source contribution to artificial mixtures, and introduction of source heterogeneity into the mixing model decreased accuracies for some source types. Aggregation of source types that could not be discriminated did not improve mixing model results. Despite providing similar discrimination accuracies as laboratory source parameters, in situ derived source information was found to be insufficient for contribution modelling.
The laboratory mixture experiment provides valuable insights into the capabilities and limitations of spectral fingerprint properties. From this study, we conclude that combinations of spectral properties can be used for mixing model analyses of a restricted number of source groups, whereas more straightforward in situ measured source parameters do not seem suitable. However, modelling results based on laboratory parameters also need to be interpreted with care and should not rely on the estimates of mean values only but should consider uncertainty intervals as well.
Hydrosedimentological studies conducted in the semiarid Upper Jaguaribe Basin, Brazil, enabled the identification of the key processes controlling sediment connectivity at different spatial scales (10(0)-10(4) km(2)).
Water and sediment fluxes were assessed from discharge, sediment concentrations and reservoir siltation measurements. Additionally, mathematical modelling (WASA-SED model) was used to quantify water and sediment transfer within the watershed.
Rainfall erosivity in the study area was moderate (4600 MJ mm ha(-1) h(-1) year(-1)), whereas runoff depths (16-60 mm year(-1)), and therefore the sediment transport capacity, were low. Consequently, similar to 60 % of the eroded sediment was deposited along the landscape, regardless of the spatial scale. The existing high-density reservoir network (contributing area of 6 km(2) per reservoir) also limits sediment propagation, retaining up to 47 % of the sediment at the large basin scale. The sediment delivery ratio (SDR) decreased with the spatial scale; on average, 41 % of the eroded sediment was yielded from the hillslopes, while for the whole 24,600-km(2) basin, the SDR was reduced to 1 % downstream of a large reservoir (1940-hm(3) capacity).
Hydrological behaviour in the Upper Jaguaribe Basin represents a constraint on sediment propagation; low runoff depth is the main feature breaking sediment connectivity, which limits sediment transference from the hillslopes to the drainage system. Surface reservoirs are also important barriers, but their relative importance to sediment retention increases with scale, since larger contributing areas are more suitable for the construction of dams due to higher hydrological potential.
The Isabena catchment (445 km(2)), Spain, features highly diverse spatial heterogeneity in land use, lithology and rainfall. Consequently, the relative contribution in terms of water and sediment yield varies immensely between its subcatchments, and also temporally. This study presents the synthesis of similar to 2.5 years of monitoring rainfall, discharge and suspended sediment concentration (SSC) in the five main subcatchments of the Isabena and its outlet.
Continuous discharge at the subcatchment outlets, nine tipping bucket rainfall and automatic SSC samplers (complemented by manual samples), were collected from June 2011 until November 2013. The water stage records were converted to discharge using a rating curve derived with Bayesian regression. For reconstructing sediment yields, the data from the intermittent SSC sampling needed to be interpolated. We employed non-parametric multivariate regression (Quantile Regression Forests, QRF) using the discharge and rainfall data plus different aggregation levels of these as ancillary predictors. The subsequent Monte Carlo simulations allowed the determination of monthly sediment yields and their uncertainty.
The Isabena catchment shows high erosion dynamics with great variability in space and time, with stark contrasts even between adjacent subcatchments. The natural conditions make water and sediment monitoring and instrumentation very challenging; the measurement of discharge is particularly prone to considerable uncertainties. The QRF method employed for reconstructing sedigraphs and monthly yields proved well suited for the task.