stable isotopic biogeochemistry of carbon and nitrogen in a perennially ice covered antarctic lake lake hoare 77 degrees 38 s 162 degrees 53 e is an amictic oligotrophic 34 m deep closed basin lake in taylor valley antarctica its perennial ice cover minimizes wind generated currents and reduces light penetration as well as restricts sediment deposition into the lake and the exchange of atmospheric gases between the water column and the atmosphere the biological community of lake hoare consists solely of microorganisms both planktonic populations and benthic microbial mats lake hoare is one of several perennially ice covered lakes in the mcmurdo dry valleys that represent the end member conditions of cold desert and saline lakes the dry valley lakes provide a unique opportunity to examine lacustrine processes that operate at all latitudes but under an extreme set of environmental conditions the dry valley lakes may also offer a valuable record of catchment and global changes in the past and present furthermore these lakes are modern day equivalents of periglacial lakes that are likely to have been common during periods of glacial maxima at temperate latitudes we have analyzed the dissolved inorganic carbon dic of lake hoare for delta 13c and the organic matter of the sediments and sediment trap material for delta 13c and delta 15n the delta 13c of the dic indicates that 12c is differentially removed in the shallow oxic portions of the lake via photosynthesis in the anoxic portions of the lake 27 34 m a net addition of 12c to the dic pool occurs via organic matter decomposition the dissolution of caco3 at depth also contributes to the dic pool except near the canada glacier where a substantial amount of allochthonous organic matter enters the lake the organic carbon being deposited on the lake bottom at different sites is isotopically similar suggesting an autochthonous source for the organic carbon preliminary inorganic carbon flux calculations suggest that a high percentage of the organic carbon fixed in the water column is remineralized as it falls through the water column at nearby lake fryxell the substantial relative to lake hoare glacial meltstream input overprints fryxell s shallow water biological delta 13c signal with delta 13c depleted dic in contrast lake hoare is not significantly affected by surface water input and mixing and therefore the delta 13c patterns observed arise primarily from biological dynamics within the lake organic matter in lake hoare is depleted in 15n which we suggest is partially the result of the addition of relatively light inorganic nitrogen into the lake system from terrestrial sources

taphonomy of a mass death layer of fishes in the paleocene paskapoo formation at joffre bridge alberta canada a layer of silty mudstone only a few centimetres thick in the lower part of the mainly fluvial paskapoo formation contains thousands of complete skeletons of fossil fish and is tiffanian late paleocene ti3 in age the diversity represented in the layer is low with thousands of specimens of a species in the trout perch family percopsidae tens of specimens of a species in the smelt family osmeridae and just two specimens of a species of osteoglossomorph in the family osteoglossidae recovered to date although the fishes occur without other kinds of fossils in the fish layer other layers in the same outcrop have yielded abundant remains of plants insects mollusks and mammals taphonomic features of the fish layer are used to test the hypothesis that it represents a mass death event and to evaluate mechanisms of formation there is little disarticulation and no sign of scavenging fish occur in distinct size classes individuals of the smelt species demonstrate breeding tubercles fish tend

sedimentology taphonomy and palaeoecology of a laminated plattenkalk from the kimmeridgian of the northern franconian alb southern germany abstract at wattendorf in the northern franconian alb southern germany centimetre to decimetre thick packages of finely laminated limestones plattenkalk occur intercalated between well bedded graded grainstones and rudstones that blanket a relief produced by now dolomitized microbialite sponge reefs these beds reach their greatest thickness in depressions between topographic highs and thin towards and finally disappear on the crests the early late kimmeridgian graded packstone bindstone alternations represent the earliest plattenkalk occurrence in southern germany the undisturbed lamination of the sediment strongly points to oxygen free conditions on the seafloor and within the sediment inimical to higher forms of life the plattenkalk contains a diverse biota of benthic and nektonic organisms excavation of a 13 cm thick plattenkalk unit across an area of 80 m2 produced 3500 fossils which with the exception of the bivalve aulacomyella exhibit a random stratigraphic distribution two thirds of the individuals had a benthic mode of life attached to hard substrate this seems to contradict the evidence of oxygen free conditions on the sea floor such as undisturbed lamination presence of articulated skeletons and preservation of soft parts however palaeoecological and taphonomic analyses indicate that the benthic faunal elements are allochthonous having settled out of suspension and thus must have been derived from hard substrate areas of neighbouring topographic highs solely the bivalve aulacomyella which occurs concentrated on a single bedding plane may have colonised the plattenkalk depression during brief periods of oxygenation alternatively a pseudoplanktonic mode of life attached to floating sea weed is envisaged for the bivalve the formation of the plattenkalk is related to local and global factors a drop in relative sea level caused the death of the microbialite sponge reefs restricted circulation in depressions between the crests of the former reefs led to anoxic conditions and the formation of finely laminated sediments stabilised by microbial mats the small depressions received sediment and skeletal elements of benthic organisms that were swept off neighbouring topographic highs by storms and that entered the depressions partly as turbidity currents partly as suspension clouds a rise in the relative sea level finally terminated the restricted circulation in the depressions and closed the taphonomic window that led to the preservation of the plattenkalk biota

fish taphonomy and environmental inference in paleolimnology abstract the contribution of fish studies to palaeoecology generally takes the form of 1 inference from analogies in modern fish faunas and 2 fish taphonomy the pattern of death and dispersal of bones 1 modern fish faunas and associated organisms provide taxonomic ecological or functional analogues for interpretation of ancient limiting factors and behaviors these inferences presume taxonomic conservatism they also presume functional relationships between morphological form and feeding mode or habitat they become weak with increased geologic age or phyletic distance between ancient subject and modern anaogue 2 fish taphonomy may contribute information about limnology community composition life history mortality depositional environment and preservation taphonomic reconstruction of ecology and preservation depends on the applicability of analogous processes in modern ecology and l limnology in aquatic taphonomy temperature is the most important factor in determining the fate of a carcass above about 16 c depending on depth and pressure most carcasses are made buoyant by bacterial decay gases and are transported to the surface where they may decay further and fall piecemeal into deepwater environments or drift to beach environments where wave energy disarticulates abrades and scatters the bones below about 16 c most carcasses remain on the bottom until buried they may be disturbed by scavengers depending on oxygen concentration in the hypolimnion

buffers barriers and blankets the dis connectivity of catchment scale sediment cascades abstract catchment configuration and the nature of connectivity within and between landscape compartments affect the operation of sediment cascades and geomorphic responses to disturbance events of differing magnitude and frequency this paper introduces the concept of landform impediments termed buffers barriers and blankets that impede sediment conveyance by limiting the connectivity between landscape compartments buffers restrict sediment delivery to channels barriers inhibit sediment movement along channels and blankets drape channel or floodplain surfaces affecting the accessibility of sediment to entrainment these features operate as a series of switches which turn on off processes of sediment delivery determining the effective catchment area at any given time using previously documented examples the role of these features in affecting the operation of sediment cascades in a low relief passive landscape setting such as the australian landmass is contrasted to examples from high relief uplifting settings in new zealand the australian examples are further explored by examining how changes to landscape connectivity brought about by human disturbance since european settlement have impacted upon landscape sensitivity and prospects for river recovery this approach to analysis of impediments to sediment conveyance is generic and can be applied in any environmental setting

taphonomic variations in eocene fish bearing varves at horsefly british columbia reveal 10 000 years of environmental change the eocene horsefly locality in british columbia has yielded many fossil fishes insects and plants its varved sediments make it ideal for study of temporal changes in environment and fish morphology several intervals of diatomaceous varves indicate a deep stratified lake setting earlier studies focused on morphological and taphonomic change during the 700 year h2 interval and morphological change during the 10 000 year h3 interval the present study uses taphonomy as an index for environmental change during the ten millennia represented by h3 comparing taphonomic changes with the morphologic changes found earlier the h3 interval records deposition in deep water indicated by dominance of the fish genera amyzon and eohiodon quiet water conditions are indicated by minimal fin disarticulation hypoxia at the time of fish death is confirmed by open mouths of most fish specimens while cool water on the lake floor prevented full flotation of fish carcasses water depth temperature and oxygenation fl

18 o modelling of freshwater inputs in baffin bay and canadian arctic coastal waters 18o salinity modelling of marine environments has been proposed for various areas including some arctic seas the present report concerns arctic coastal waters collected along the west coast of greenland northern baffin bay the arctic archipelago and the north shore of alaska measurements of 18o versus salinity allow the identification of three main components marine standard water continental freshwater and sea ice meltwater continental waters may be represented by either glacial meltwater western greenland land drainage mackenzie areas or both quantitative determinations of the respective parts involved in mixed coastal waters imply a precise knowledge of the isotopic characteristics of the local continental waters these determinations may be achieved either numerically or graphically

sedimentology of perennial ice covered meromictic lake a ellesmere island at the northern extreme of canadapolar continental shelf program contribution 00109 the sedimentology of coastal meromictic lake a ellesmere island 83 00 n 75 30 w was investigated to understand the linkages between the extreme lake environment and its sedimentary features four facies were identified within the sedimentary record that represent stages of the lake s development from a marine embayment to a meromictic lake despite low ecosystem productivity both clastic and biogenic materials contribute substantially and highly seasonal sedimentation pervasive ice cover and anoxia in the saline bottom water monimolimnion act to preserve annual sedimentary units varves within the upper part of the sedimentary record sediment texture is predominantly silt and clay but the irregular presence of sand indicates past episodes of higher energy stream discharge to the lake oxygen incursions into the chemocline likely cause bacteria mortality and provide elemental sulphur for iron sulphides that are deposited in the sediments millimetre scale sedimentary pellets are also a consp

a field investigation into the effects of progressive rainfall induced soil seal and crust development on runoff and erosion rates the impact of surface cover abstract surface crusts and seals can form from a variety of processes both physical and biological and have the potential to alter runoff and erosion especially in regions with low vegetation covers despite the obvious links between seals and crusts these features have rarely been considered together this study uses rainfall simulation experiments to investigate interrill soil crust and seal development in response to structural or raindrop impact induced and depositional or runoff induced processes on a semiarid piedmont in southern new mexico usa which has undergone substantive vegetation change replacement of grasses by shrubs over the last 100 years the study design incorporates six double paired runoff plots divided into four subplots each of which was exposed to three rainfall simulation events crust development on these plots was assessed using penetration resistance measurements while seal development was assessed using runoff coefficients the penetration resistance data indicate that subplots directly exposed to raindrop impacts uncovered plots have crusts that are 40 stronger than those positioned beneath a mesh cover covered plots that intercepts the kinetic energy of the rainfall the crusts exposed to raindrop impacts increased in strength following each simulation whereas the crusts on the covered surfaces reached a plateau after two events runoff data indicate that seal development does not directly mirror crust formation runoff coefficients increased after each rainfall simulation event but were not significantly different between the covered and uncovered plots rather the presence of stone lags or litter on the soil surface influenced the relation between runoff and seal development sediment yields from uncovered surfaces exceeded those from covered surfaces indicating that raindrop impacts contribute to the delivery of sediment into flows the results of this study indicate that the loss of vegetation cover on the piedmont has increased the extent of surface crust and seal development but that those crusts may be playing an important role in mitigating erosion

fractal features of soil particle size distribution in layered sediments behind two check dams implications for the loess plateau china abstract the layered sediment deposited behind a check dam can provide useful information about soil erosion processes in the dam controlled area this study aims to evaluate the possible fractal nature of layered sediments behind check dams assessing whether fractal dimension can serve as a feasible index for evaluating the impact of land use types on the area controlled by the check dam fractal dimension measurement was employed to analyze the features of soil particle size distribution psd for different layered sediments of the shipanmao and zhangshan check dams in the dalihe river basin of the loess plateau china results show that the predominant soil particle sizes of the sediment layers behind the shipanmao and zhangshan dams are silt clay cv for the coarse sand fraction is highest followed by the fine sand and the silt clay size fractions larger soil particle sizes coincide with larger cv values the fractal dimension d m of the psd ranges from 2 111 to 2 219 and 2 144 to 2 447 for shipanmao and zhangshan respectively the d m values tend to increase and decrease for the layered sediments from top to bottom with some turning points the turning points of d m are related to the trends of the soil psds in the adjacent sediment layers although d m has significant positive and negative correlations with the silt clay and the fine sand size fractions respectively no correlation with the coarse sand fraction was observed soil psd is a more dominant factor affecting d m than the time lag between soil erosion and sediment deposition overall d m decreased for shipanmao during the deposition period 1972 1979 the total increment of the c factor in the universal soil loss equation and the soil erosion amount per rainfall erosivity were applied to analyze land use changes between 1972 and 1979 for the dam controlled area of the shipanmao dam the total increment of c during 1972 1979 was 0 021 and the soil erosion amount per rainfall erosivity was smaller in 1972 than in 1979 indicating desertification in the dam controlled area in addition the land use types prevalent in 1979 were more prone to soil loss than those in 1972 d m is a useful parameter to assess land use types and soil degradation processes in dam controlled areas of the loess plateau

holocene records of effective precipitation in west greenland holocene changes in effective precipitation precipitation evaporation p e were reconstructed for the sondre stromfjord region of southwest greenland using the sediment records of two neighbourin

modelling sediment transport capacity of rill flow for loess sediments on steep slopes abstract sediment transport is an important aspect of soil erosion and sediment transport capacity tc is a key to establishing process based erosion models a lot of studies exist that have determined tc for overland flow however few studies have been conducted to determine tc for loess sediments on steep slopes experimental data for this region are thus needed the objectives of this study are to formulate new equations to describe tc and evaluate the suitability of these equations for loess sediments on steep slopes the slope gradients in this study ranged from 10 51 to 38 39 and flow discharges per unit width varied from 1 11 10 3 m2 s 1 to 3 78 10 3 m2 s 1 results showed that tc increased as a power function with flow discharge and slope gradient with r2 0 99 and nash sutcliffe model efficiency nse 0 99 tc was more sensitive to flow discharge than slope gradient tc increased as a power function with mean flow velocity which was satisfied to predict tc with r2 0 99 and nse 0 99 shear stress r2 0 89 nse 0 88 was also a good predictor of tc and stream power r2 0 96 nse 0 96 was a better predictor of tc than shear stress however unit stream power was not a good predictor to estimate tc in our study with r2 0 63 and nse 0 62 these findings offer a new approach for predicting tc for loess sediments on steep slopes

evidence of density currents with the potential to promote meromixis in ice covered saline lakes abstract ice covers all but the most saline of the vestfold hills lakes for about 8 12 months of each year and precludes wind induced turbulent mixing over the winter when strong winds are most frequent nevertheless the progressive growth of ice volume through the austral winter and spring months generates haline convection capable of mixing the water column to a depth at least as great as that achieved by wind induced turbulence in the summer ice free period further cold and very saline brines may form at the shallow periphery of a lake and flow downslope penetrating to the lake centre below the convectively mixed layer detailed temperature profiles of hypersaline organic lake provide the first evidence for these density currents in saline lakes of the vestfold hills these data indicate a dynamic responsiveness to periods of relatively cold weather and that the resulting density currents may be sufficiently small in volume to have little effect on the anoxia of bottom layers in these meromictic lakes alternating periods of negative and positive water balance may also be significant in the formation and destruction of meromixis in these saline lakes which lack outflow streams if a lake has been through a period of negative water balance becoming relatively more saline and then begins to be diluted during a subsequent period of positive water balance the winter haline convection will penetrate to progressively shallower depths and deeper layers may stagnate marking the onset of meromixis an increase in the water level of organic lake over ten years indicates the speed with which the vestfold hills lakes may experience significant change in salinity despite the generally small catchments of these lakes

taphonomic analysis of fish in rift lacustrine systems environmental indicators and implications for fish speciation abstract two rift basin lacustrine successions cacheuta and los rastros formations in the middle triassic of argentina were studied to test two different hypotheses 1 fish taphonomy is useful as an indicator of environmental conditions for these two paleolakes and 2 fish taphonomy is useful for understanding environmental effects on speciation the fish fossils are found in two lacustrine deposits as isolated and disarticulated scales and cranial bones clumps and stringers of scales articulated body segments and complete specimens four taphofacies are defined for cacheuta specimens ca a to ca d and three taphofacies are defined for los rastros fish assemblages lr a to lr c a principal components analysis was performed with the taphonomic features supporting the seven taphofacies defined a taphonomic model is proposed that characterizes a lacustrine deltaic environment developed in the rift basin and identifies three sub environments each one with its particular fossil assemblages the fish assemblages in the los rastros formation suggest that the fishes preserved in delta front and turbidity current deposits lr b and lr c taphofacies were allochthonous to the lake and probably inhabited the delta plains and affluent fluvial system in contrast the isolated fish remains preserved in open lake deposits lr a taphofacies likely represent both autochthonous and or allochthonous specimens in the cacheuta formation articulated and isolated fish remains preserved in open lake deposits ca a and ca d tafofacies might represent autochthonous lacustrine specimens based on the good preservation of the material the fish remains preserved in underflow and turbidity current deposits ca b and ca c taphofacies were allochthonous to the lake and probably inhabited the delta plain and affluent fluvial system the fish taphonomic study of two different rift basin lacustrine successions allows test of the two proposed hypotheses fish taphonomy was useful as an indicator of environmental conditions beacuse the differences in fish preservation allowed differentiation of the sub environments and reconstruction of the environmental conditions and dynamics of the rift lake basins also fish taphonomy was useful for understanding environmental effects on speciation by characterizing the environments and dynamics that promote the development of new fish species recognizing fish inhabited environments and identifying the generalist and specialist species

hydrological responses and soil erosion potential of abandoned cropland in the loess plateau china recent changes in hydrological processes and soil erosion in the loess plateau china are immediate responses to cropland abandonment for revegetation which lead to a long term decrease in runoff generation and soil erosion however detailed hydrological responses and soil erosion changes have not been clearly evaluated in this study two issues were focused on the plot scale the first issue relates to changes in vegetation cover and soil properties during the early stages of revegetation given the occurrence of soil compaction it was hypothesized that runoff increased during this period and the soil erosion did not significantly decline even though vegetation increased the second issue is the effect of scale on runoff and soil erosion three plot groups of three vegetation types and two restoration stages were established for comparative experiments the results from these experiments confirmed that the soil compaction occurred during revegetation in this region greater runoff was produced in plot group that experienced both a longer restoration time and with higher vegetation cover such as groups 2 and 3 in this study than that with a shorter restoration time and lower vegetation cover group 1 in addition the total soil loss rates of all plot groups were rather low and did not significantly differ from each other this indicates that a reduction in runoff generation and soil erosion as a result of revegetation was limited in the early stages of restoration following the cropland abandonment with increasing plot area the runoff coefficient decreased for the plot group with a longer revegetation time groups 2 and 3 but gently increased for the one with a shorter restoration time group 1 in groups 2 and 3 soil loss rate decreased when plot area enlarged in group 1 it decreased before a plot area threshold of 18 m 2 was exceeded however the increase occurred when plot area crossed the threshold value in conclusion the high vegetation cover alone did not lead to reduction in the runoff coefficient during the early stages of revegetation when evaluating hydrological and soil erosion responses to revegetation the soil compaction processes should be considered additionally the effect of scale on runoff and soil erosion was found to be dependent on restoration extent and thus on restoration time c 2011 elsevier by all rights reserved

controlling factors of loess landslides in western china based on detailed field data from recent geo hazards surveys in the loess plateau region of western china this study analyzes the key factors that control loess landslides the evolution phase of river valleys the geological structure of slopes and the geometry of slopes are all found to play a role in determining the occurrence distribution and other characteristics of loess landslides groundwater and vegetation also contribute to their formation a combination of human engineering activities and precipitation events are the principal triggering factors for the instability of loess slopes

paleolimnology and taphonomy of some fish deposits in fossil and uinta lakes of the eocene green river formation utah and wyoming abstract in four sections in the lacustrine eocene green river formation in utah lake uinta fish are preserved on carbonate mudflats along high energy carbonate shorelines in the littoral zone and in deeper profundal areas scattered bones and scales are found throughout dropped from disintegrating floating carcasses gar scales typify shallow water deposits partly due to habitat preference beach concentrations of greatly abraded bones and scales grade offshore into storm lag layers and lenses which grade to loosely packed horizons or patches of unworn remains littoral fish fossils range from dropped bones to good skeletons with much floating lifting and scavenging preservation improves away from the waterline not only into deep and cold profundal waters where the carcasses are protected from scavenging by anoxia and prevented from floating by temperature and pressure but also onto mudflats where stranding and burial of carcasses can also protect them a section through an isolated part of the green river formation in wyoming fossil lake also ranged from profundal to littoral with minor emergence dropped body parts were found throughout but preservation quality of the best specimens improved with presumed depth the beds with the best specimens seem to have accumulated at the bottom of a deep stratified warm monomictic lake our lake uinta sections were generally shallower and suggest more fluctuations in water level but this is not relevant to broad paleolimnological interpretations because they represent marginal zones which are necessarily more sensitive to changes in depth overall fish fossils are especially informative in deeper waters where sedimentary distinctions fail

hydrological processes in a small arid catchment scale effects of rainfall and slope length many studies have been concerned with the scale issue in geomorphology and hydrology most studies focus on the possibility of data transfer from small to large watersheds less attention has been given to the scale problem within very small watersheds where differences in slope length may seriously affect the spatial distribution and extent of runoff contributing areas to the channel it is usually assumed that runoff and erosion increase as slope length and angle increase however field observations in the negev highlands show positive relationships between slope length and deposition rates regardless of slope angles short hillslopes are devoid of colluvial mantle while thick colluvial deposits with well developed soil profiles indicative of long term stability are found at the base of long hillslopes the hypothesis advanced is that temporal variations in effective rainfall control the spatial structures of surface properties that further enhance the effects of temporal variations in rainfall long term monitoring of rainfall and runoff 1982 1998 conducted at spatial scales varying from few hundreds of m2 up to 0 3 km2 show a decrease in runoff at the hillslope scale the low efficiency of runoff and erosion processes on long hillslopes is because the concentration time required for continuous flow along such slopes is longer than the duration of most effective rain showers prevailing in the area field data lead to the notion that runoff and erosion models in which a positive relationship between slope length and angle and runoff and erosion rates is assumed should not be applied to arid and semiarid areas more attention should be given in latter areas to the complex hydrological relationships between rainfall scales and spatial scales the implications of data obtained regarding the spatial distribution of areas contributing to channel flow at a geological time scale and under changing climatic conditions are discussed

the chemical development of a hypersaline coastal basin in the high arctic we investigated a hypersaline seasonally isolated marine basin simb in the canadian high arctic to elucidate the role of brine rejection tidal forcing and groundwater input over the formation of hypersalinity analyses of physical parameters and seasonal sampling of ionic and isotopic composition were carried out on a coastal basin near shellabear point melville island northwest territories 75 n 113 w observations reveal daily and seasonal variability in the water column due to a seasonal tidal connection during the ice free season which lasts substantially longer than the period of freshwater inflow from the catchment an ice formation model of the volume of brine rejected from surface ice formed from marine water indicates that rapid saline enrichment of the basin due to ice formation is possible from tidally replenished marine water and that the current hypersalinity may have formed in less than a decade modeled isotopic composition of brines are consistent with observations and provide an alternative to freshwater isotopic dilution suggested by other workers a tidal connection is a critical consideration in lake evolution and many hypersaline polar lakes could have developed their current chemical composition before full marine isolation by contrast in some coastal lakes marine stratification caused by ice shelves before isolation provides a setting for minimal brine formation and subsequent meromictic conditions to develop hence the marine setting at the time of isolation represents a key factor in explaining divergent lake chemical evolution in the high arctic

modelling sheet erosion on steep slopes in the loess region of china abstract the relationship of sheet erosion rate se slope gradient s and rainfall intensity i and hydraulic parameters such as flow velocity v shear stress stream power and unit stream power p was investigated to derive an accurate experimental model the experiment was conducted at slopes of 12 23 17 63 26 8 36 4 40 4 and 46 63 under i of 48 60 90 120 138 and 150 mm h 1 respectively using simulated rainfall results showed that sheet erosion rate increased as a power function with rainfall intensity and slope gradient with r 2 0 95 and nash sutcliffe model efficiency nse 0 87 sheet erosion rate was more sensitive to rainfall intensity than to slope gradient it increased as a power function with flow velocity which was satisfactory for predicting sheet erosion rate with r 2 0 95 and nse 0 81 shear stress and stream power could be used to predict sheet erosion rate accurately with a linear function equation stream power r 2 0 97 nse 0 97 was a better predictor of sheet erosion rather than shear stress r 2 0 90 nse 0 89 however a prediction based on unit stream power was poor the new equation i e se 7 5 10 12 s 1 43 i 3 04 and se 0 06 0 0003 and se 0 011 0 01 would improve water erosion estimation on loess hillslopes of china

isotopic analyses 18o 13c 14c of two meromictic lakes in the canadian arctic archipelago1 meromictic lakes garrow and sophia in the canadian arctic archipelago were sampled to establish the origin and age of their waters by isotopic studies the ow 8o values reflect the permanent stratification of the waters in both lakes the mixolimnia contain waters with an isotopic signal between 13 16 and 2 1 98o oo coherent with the values for precipitation in these high latitudes the short residence time of the water in this layer makes it possible to record episodic variations of the freshwater inputs to the lakes in the chemoclines the al80 values increase to 10 concomitantly with a rise in chloride content to 42 g liter this corresponds to a conservative mixing of surficial and deep waters in the monimolimnia hypersaline waters up to 2 5 times the salinity of seawater show negative 6180 values ca 8 these waters result from brine production during permafrost growth in the watershed according to a rayleigh process the brines drained toward the deepest part of each lake after postglacial uplift and became isolated 14c dating of total inorganic carbon in the lake garrow monimolimnion gave an age of 2 580 260 years b p in lake sophia the deep waters exhibit recent 14c activity 12 1 4 modern carbon that suggests recent infiltration of seawater into the lake basin

biomarkers in sedimentary sequences indicators to track sediment sources over decadal timescales abstract long term sedimentary sequence research can reveal how human activities and climate interact to affect catchment vegetation flooding soil erosion and sediment sources in this study a biomarker sediment fingerprinting technique based on n alkanes was used to identify long timescale decadal sediment sources in a small agricultural catchment however the highly saline carbonate environment and bacterial and algal activities elevated the levels of even chain n alkanes in the sediments leading to an obvious even over odd predominance of short and middle components c 15 c 26 therefore by analyzing three odd long chain n alkanes c 27 c 29 and c 31 in 27 source samples from cropland gully and steep slope areas and one sediment sequence one cultivated horizon and 47 flood couplets a composite fingerprinting method and genetic algorithm optimization were applied to find the optimal source contributions to sediments the biomarker fingerprinting results demonstrated that the primary sediment source is gullies followed by cropland and steep slope areas the average median source contributions associated with 47 flood couples collected from sediment core samples ranged from 0 0 1 to 91 9 0 4 with an average of 45 0 for gullies 0 0 4 to 95 6 1 6 with an average of 38 2 for cropland and 0 2 1 to 60 7 0 4 with an average of 16 8 for steep slopes however because farmers were highly motivated to manage the cropland after the 1980s over half the sediments were derived from cropland in the 1980s biomarkers have significant advantages in the identification of sediments derived from different landscape units e g gully and steep slope areas and n alkanes have considerable potential in high resolution research of environmental change based on soil erosion in the hilly loess plateau region

paleolimnology evolution in rift basins the ischigualasto villa union basin central western argentina during the triassic abstract extensional basins offer a high preservation potential for sedimentary and fossil records nonmarine rift basins contain diverse environments including fluvial and lacustrine lake deposits have long been recognized as significant archives of the paleoenvironmental record the ischigualasto villa union basin represents the only nearly continuous continental triassic record with up to 6000 m of alluvial fluvial and lacustrine deposits the deep lacustrine interval is known as the los rastros formation and consists of several lacustrine deltaic cycles a detailed facies analysis allowed the characterization of five facies associations and two types of cycles 1 a shoreline dominated progradational type i cycle containing facies association a offshore lacustrine deposits and facies association b marginal palustrine deposits along the shoreline of the lake or facies association c lacustrine siliciclastic coastal deposits and 2 a delta dominated progradational type ii cycle characterized by facies association a offshore lacustrine and prodelta deposits facies association d delta front deposits and facies association e delta plain deposits the sedimentary evolution of the chanares los rastros sequence is defined within this extensional setting as one depositional sequence with three system tracts lowstand transgressive and highstand system tract biotic abiotic and sedimentologic data allowed the interpretation of the limnologic dynamics of the los rastros paleolake as a deep freshwater lake within a half graben exhibiting meromixis and showing a change from moderate eutrophic conditions with low oxygen content to relatively oxygenated oligotrophic conditions the successive fluctuations recorded in lake level are considered in the sequence stratigraphic framework of bohacs et al to reflect the relative balance of sediment and water input versus accommodation in an overfilled lacustrine basin

combined stratigraphic and isotopic studies of triassic strata cuyo basin argentine precordillera the evolution of the triassic cretaceous cuyo basin located in the andean precordillera nw argentina was mainly controlled by extensional transtensional tectonics along nw trending structures inherited from paleozoic sutures stratigraphic and isotopic studies are herein presented in order to constrain the sedimentary infilling and source areas as well as the age of triassic strata related to the active faulted margin of the cacheuta sub basin the whole stratigraphic package of the cuyo basin is interpreted as a second order depositional sequence comprising lowstand alluvial fan deposits transgressive fluvial deltaic and facustrine deposits and highstand oxidized lacustrine and high sinuosity luvial deposits systems tracts this stacking pattern was mainly controlled by the interplay between sedimentary influx and accommodation space with important volcaniclastic contribution especially during the early stages of basin development sm nd depleted mantle model ages tdm for both basement and volcano sedimentary samples range from 867 to 1345 ma all samples have negative end t values 0 33 to 5 02 basal deposits present older tdm model ages compared to intermediate positioned deposits and upper deposits present a wider range of model ages this time integrated factor correlates with paleocurrent data which indicate changes in the source areas through time the nd isotopic signature also suggests that sources of sediments for the cacheuta sub basin during the triassic were restricted to units of mesoproterozoic grenvillian age probably related to the cuyania terrane the u pb sensitive high resolution ion microprobe shrimp zircon age of 243 5 ma obtained in juvenile magmatic zircons from a lithoclast free ignimbrite interlayered within the basal alluvial fan facies of the cacheuta sub basin places the lowstand deposits in the olenekian and establishes a potential chronostratigraphic horizon for future correlations

use of reservoir deposits to reconstruct the recent changes in sediment yields from a small granite catchment in the yimeng mountain region china information on recent changes in sediment yields from small catchments provides a better understanding of temporal trends in soil loss from certain physical and human influenced landscapes that have been subjected to recent environmental changes and will help bridge the current knowledge gap that exists between hillslope erosion and sediment transport in rivers the yimeng mountain region characterized by alternating granite and limestone is one of the most susceptible regions to soil erosion in northern china and has been subjected to intensive anthropogenic activity in recent years soil loss from areas underlain by granite is particularly obvious and is the main sediment source for the yihe river in this study we used reservoir deposits to estimate the changes in sediment yields over the past 50 years from a small catchment underlain by granite namely the jiangzhuang catchment in the yimeng mountain region three cores were collected from the jiangzhuang reservoir in the catchment the activities of 137cs and 210pbex at different depths clay grain size 5 m contents and sedimentary organic carbon soc contents in the cores were analysed with reference to human activity and environmental change in the catchment the chronologies of the cores were established by 137cs and 210pbex dating the area specific sediment yield ssy for different time periods since dam construction was estimated from each core by referring to the original capacity curve of the reservoir the results indicate that the depth profiles of 137cs 210pbex clay and soc contents in cores from the jiangzhuang reservoir reflect the general history of human disturbances on the catchment over the past 50 years the estimated ssy value from each core for each period ranged from 7 2 2 7 to 23 7 8 3 t ha 1 y 1 with a mean of 12 5 4 6 t ha 1 y 1 ssy decreased during 1954 1972 and then showed a general tendency to increase the temporal pattern of the sediment yield largely reflects the history of environmental change influenced by human activity in the catchment

effectiveness of vegetation barriers for marly sediment trapping vegetation barriers can be effective in trapping eroded sediment but little knowledge exists on the characteristics of vegetation barriers efficient in trapping all sediments from an eroded zone upslope the objective of this study is to quantify the effectiveness of vegetation barriers for marly sediment trapping relationships between eroded zones and vegetation barriers composed of low vegetation that is to say herbaceous and under shrub layers located downslope and sufficient to stop all the sediments eroded above have been studied in the brusquet experimental marly catchment in the french southern alps 40 plots with surface areas less than 500 m were studied the eroded zones and the vegetation barriers were characterised by their surface areas between which an average linear relationship exists results also showed that for a marly plot with a given surface area a downslope vegetation barrier covering only 20 of this plot can be sufficient to trap all the sediments eroded above it

effect of natural restoration time of abandoned farmland on soil detachment by overland flow in the loess plateau of china vegetation restoration has significant effects on soil properties and vegetation cover and thus affects soil detachment by overland flow few studies have been conducted to evaluate this effect in the loess plateau where a great green project was implemented in the past decade this study was carried out to quantify the effects of age of abandoned farmland under natural vegetation restoration on soil detachment by overland flow and soil resistance to erosion as reflected by soil erodibility and critical shear stress the undisturbed soil samples were collected from five abandoned farmlands with natural restoration age varying from 3 to 37 years the samples were subjected to flow scouring in a 4 0 m long by 0 35 m wide hydraulic flume under six different shear stresses ranging from 5 60 to 18 15 pa the results showed that the measured soil detachment capacities in currently cultivated farmland were 24 1 to 35 4 times greater than those of the abandoned farmlands for the abandoned farmlands soil detachment capacities fluctuated greatly due to the complex effects of root density and biological crust thickness and could be simulated well by flow shear stress and biological crust thickness with a power function nse 0 851 soil erodibility of abandoned farmlands decreased gradually with restoration age and reached a steady stage when restoration age was greater than 28 years the critical shear stress of the natural abandoned farmlands declined when restoration age was less than 18 years and then increased due to the episodic influences of vegetation recovery and biological crust development more studies in the loess plateau are necessary to quantify the relationship between soil detachment capacity and biological crust thickness for better understanding the mechanism of soil detachment under natural vegetation restoration copyright 2013 john wiley sons ltd

scale effects on specific sediment yield in the yellow river basin and geomorphological explanations based on data from 199 stations in the yellow river drainage basin for which more than 5 years of data are available the relationship between specific sediment yield ys and drainage area a has been studied this relationship for the yellow river basin is different from those for many other rivers of the world both at the scale of whole basin and at local scales with increasing basin area the specific sediment yield increases reaches a maximum and then declines the non linear variation in the ys a relationship can be explained by first surface material distribution second adjustment of the basin at macro time and space scales and the third the variation of energy expenditure with drainage basin scale as the loess deposits in the high relief headwater areas is thin it can be exhausted much more rapidly by flowing water erosion than in other areas so the underlying erosion resistant bedrock may be exposed much earlier in many rivers in the study area bedrock is exposed in the upper part of the drainage basin and loess appears in the middle part with a thickness that increases downstream to a peak followed by a decline due to the influence of these spatial patterns of surface material distribution a spatial pattern of specific sediment yield appears the non linear ys a relationship may be interpreted as an indication that the fluvial system of the yellow river is still at the stage of strong adjustment to the environmental change of pleistocene holocene transition especially to the change of dominant geomorphic agency from wind to flowing water this non linear relationship can also be explained by the variation of stream power with the drainage basin scale the stream power increases with drainage area to a peak value and subsequently decreases a trend that is similar to the trend of the ys a relationship

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

reconstruction of ancient lake environments using both autochthonous and allochthonous fossils abstract eocene lacustrine paleoenvironments in western north america have been reconstructed using evidence from assemblages of autochthonous and allochthonous fossils seasonal variation is recorded in varved sediments that contain fossil assemblages indicative of deep water off shore deposition stratigraphic variation at one locality records a transgression from a coal swamp through near shore lacustrine environments to more off shore lacustrine environments fish assemblages preserved in this section change in the taxa represented and in the taphonomic characteristics of their preservation terrestrial fossils insects and plants change in abundance concomitantly a large proportion of the taxonomic and taphonomic variation between fish assemblages from other formations and localities is directly correlated with the near shore to off shore variation insect and plant assemblages also differ greatly between near shore and off shore depositional environments if one s goal is to reconstruct ancient lacustrine communities sampling programs must be designed to compensate for these biases

soil erosion rates on sloping cultivated land on the loess plateau near ansai shaanxi province china an investigation using 137cs and rill measurements sediment yields from the rolling hills area of the loess plateau in northern china 10 000 25 000 t km 2 yr 1 are amongst the highest in the world the sediment is believed to derive from both the deep gullies that dissect the rolling plateau and the steep cultivated fields on the slopes of the mounds between the gullies however there are few reliable data for erosion rates on the cultivated fields and it is suspected that current estimates 10 000 16 000 t km 2 yr 1 based on empirical relationships derived from erosion plot studies exceed the true values this study sought to address the need for more information concerning erosion of the cultivated fields through derivation of erosion rates from measurements of rill volume and caesium 137 cs 137 inventories for typical fields near the village of ansai shaanxi province the derived erosion rates are discussed and compared with estimates based on empirical relationships derived from erosion plot data where erosion rate estimates based on both rill volume data and cs 137 inventories are available they show good agreement in the pattern of downslope variation both show a sharp decline in erosion rates at a slope length of c 50 m this is tentatively attributed to a change from transport limited to detachment limited conditions where rill incision reaches the undisturbed loess at the base of the plough layer no such decline is visible in the predictions based on empirical relationships derived from erosion plot data further evidence is presented that supports the suggestion that these empirical relationships overestimate erosion rates at slope lengths in excess of c 50 m it is tentatively suggested that the rates of soil erosion from sloping cultivated fields in the rolling hills area are more likely to lie in the range 8000 10 000 t km 2 yr 1 than in the higher range suggested by the empirical relationships c 1998 john wiley sons ltd

paleoecology and sedimentology of a late triassic lake culpeper basin virginia u s a late triassic and early jurassic lacustrine sedimentary rocks in the culpeper basin northern virginia and maryland u s a locally contain abundant fossil ostracodes darwinula sp conchostracans clam shrimp cyzicus sp and cornia sp fish and plant fragments stromatolites pelecypods notostracans tadpole shrimp triops cf cancriformis and insects are known from some late triassic beds and freshwater gastropods have been reported from the early jurassic of the culpeper basin a 7 m thick late triassic lacustrine sequence exposed in the central part of the culpeper basin records the history of a perennial saline lake the lake deposits consist chiefly of olive gray mudstone and claystone with interbedded sandstone and siltstone and stromatolitic limestone in the upper part evaporite crystal molds and pseudomorphs are present locally in the central part of the sequence indicating saline conditions red laminated and cross laminated sandstone and siltstone beds at the top and near the bottom of the sequence were deposited by fresh water inflow to the lake marginal lacustrine deposits associated with these fluvial redbeds contain abundant faunal remains including ostracodes conchostracans notostracans and scarce fish remains and insects these organisms were restricted to relatively fresh water near the lake margins faunal remains are absent from the central saline part of the lake sequence

the carbon isotopic composition of dissolved inorganic carbon in perennially ice covered antarctic lakes searching for a biogenic signature the stable isotopic signature of dissolved inorganic carbon dic has been routinely used in temperate lake systems to investigate the biogeochemical dynamics of carbon we studied seven perennially ice covered lakes in the mcmurdo dry valleys antarctica to ascertain how carbon cycling affects the d 13 c of dic in water columns of these systems unlike temperate lakes and in fact most polar lake systems the permanent ice covers of these lakes eliminate physical mixing turnover and hence redistribution of dic in the lakes as well as minimize co2 exchange with the atmosphere these important and unique physical constraints have significant impact on carbon dynamics in the lakes and important consequences for the d 13 c distribution the geochemistry in these lakes is influenced in varying amounts by landscape position hydrologic input and their evolutionary history five of these lakes both lobes of lake bonney and lakes fryxell miers and vanda have surface water d 13 c ratios of 0 4 lake hoare has more negative values while lake joyce the highest elevation lake has a much higher value 10 5 all of the lakes have upper to mid depth d 13 c maxima reflecting biological uptake of 12 c only four of the lakes lakes vanda joyce hoare and fryxell have deep waters with negative values of d 13 c implying rigorous remineralization of 12 c at depth lake miers the only lake that is not closed basin has the smallest d 13 c variation with depth indicating that hydrologic exchange greatly influences the d 13 c signal

gully and sheet erosion on subtropical mountain slopes their respective roles and the scale effect abstract as most mountains in tropical and subtropical zones the western sierra madre suffers active present erosion which may create some constraints to the social and economic development in the area the objectives of this study of soil degradation in the western sierra madre are to determine the respective roles of gully and sheet erosion this research is based on field observations field measurements of runoff and soil losses at the plot as well as the watershed scales as an analysis of an exhaustive census of the few gullies located in an experimental area measured soil losses in the western sierra madre are high although there are few gullies most of the sediment yield seems to originate in widespread degraded areas where stoniness is the main evidence of a previous stage of erosion previously overgrazing and deforestation were determined as the factors of the appearance of new soil surface characteristics which explain the high runoff and sediment productions the soil compacted by cattle trampling reduces infiltration the decrease of the vegetation cover triggers a rise in the splash effect and thus a soil sealing these processes induce an increase in runoff and soil losses the main erosion type has been described as sheet erosion it is characterised by the removal of fine soil particles and the remains of gravels pebbles and blocks which constitute a pavement on the soil gullies generally appear on the bottom of wide valleys and depressions where soils are thick it is shown that sheet erosion is two orders of magnitude higher than gully erosion at the hillslope scale due to the spatial distribution of land use and the geological context such as the heavily degraded areas close to the main rivers the reduction of runoff and soil loss rates within the extension of a considered area commonly observed in hydrology only applies up to the elementary catchments scale 1 to 50 km 2 above this area runoff coefficient and soil loss rates increase

effects of watershed management practices on the relationships among rainfall runoff and sediment delivery in the hilly gully region of the loess plateau in china abstract the relationships among rainfall runoff and sediment delivery are significant in predicting soil erosion and in evaluating the benefits of watershed management practices wmp on the hilly gully regions of the loess plateau hydrologic data 1987 to 2010 were analyzed for variations in precipitation runoff and sediment delivery at annual and event scale these data were obtained from the qiaozi east watershed qe and the qiaozi west watershed qw with and without wmp respectively results indicated that the runoff coefficients of the watersheds decreased significantly although the runoff coefficient of qe was less than half of that of qw sediment delivery decreased more in qe than in qw mainly because of the increase in vegetation cover in both watersheds in qe the relationship between runoff and sediment delivery did not change significantly from 1987 to 2006 although the variation was significant from 2007 to 2010 in qw the relationship between runoff and sediment delivery was not notably altered from 1987 to 2010 this finding suggested that vegetation practices and engineering measures on the hillslope did not strongly affect the relationship between runoff and sediment delivery in the watersheds but the construction of check dams reduced gully erosion and the suspended sediment concentration hence control practices for gully erosion significantly influenced the relationship between runoff and sediment delivery this study suggests that a combination of hillslope and gully erosion control practices effectively reduces erosion and sediment delivery in the hilly gully regions of the loess plateau