Dry Valleys Research Articles

Spatial Patterns of Major Ions and Their Relationship to Sediment Concentration in Near Surface Glacier Ice, Taylor Valley Antarctica

AbstractGlaciers form the headwaters of many watersheds and, in arid polar environments, can provide the vast majority of water to downstream systems. Headwater watersheds are critically important for setting the chemistry for downstream systems, yet we know comparatively little about the patterns and processes that generate the geochemical signature of meltwater on glacier surfaces. Here, we focus on glaciers in the McMurdo Dry Valleys of Antarctica, the largest ice‐free area on the continent, characterized by alpine glaciers flowing into broad, rocky valleys. We examine patterns from the coast inland, accumulation to ablation zones, laterally across individual glaciers, and through the zone of meltwater generation. We directly compare solutes to sediment concentrations, a major source of dissolved solutes. Our findings agree with previous work that the overall meltwater chemistry of a given glacier is a product of local sediment sources and regional wind patterns: foehn winds moving from the ice sheet to the coast and on‐shore sea breezes. Further, these patterns hold across an individual glacier. Finally, we find that the ice chemistry and sediment profiles reflect freeze‐thaw and melt processes that occur at depth. This indicates that the transport and weathering of sediment in the ice profile likely has a strong influence on supra‐ and proglacial stream chemistry. This new understanding strengthens connections between physical and geochemical processes in cold‐based polar glacier environments and helps us better understand the processes driving landscape and ecosystem connectivity.

THE INFLUENCE OF GEOLOGICAL AND GEOMORPHOLOGICAL FACTORS ON THE CREATION OF A NETWORK OF FOUR LAKES IN THE TALAS VALLEY.

  In the article " Influence of geological and geomorphological factors on the creation of a network of tortkols in the Talas Valley", the aim of the work is to clarify the geological and geomorphological conditions in the Talas River basin that contributed to the selection of sites for the construction of tortcoles - outposts of the Middle Ages. Geological and geomorphological analysis of the locations of the tortcoles allowed us to identify the patterns of their localization. So, along with the main riverbed, the branches, channels and dry valleys of a large area of the Pritalasye were of great importance. The following conditions favored the emergence of a dense network of tortkols: strategic location, availability of water sources and raw materials for housing construction, water availability of adjacent territories. All these factors directly depended on the geological and structural features and relief of this territory. This study allows us to identify patterns in the choice of the main routes of movement of caravans and the localization of points that perform a security function. Key words: Talas valley; Shu-Talas trough; medieval torkoli; alluvial plain; Late Anthropogenic alluvial fan; floodplain; terraces; anticlines; kersh; loams; rocks of the Andasai Formation

Soil erosion and anthropogenic impact on landscape evolution over the past 2500 years: A case study of the Villers-Ecalles dry valley (Seine-Maritime, Normandy, France)

The present study analyzes archaeological and pedo-geomorphological data gathered from a Protohistoric settlement in Normandy (Northwestern France), in order to characterize upper Holocene landscape evolution, as well as to assess the impact of erosional processes in relation to human occupation over the past 2500 years. The settlement studied herein is located on the Pays de Caux plateau, in Villers-Ecalles, where luvisols, which have developed on Upper Pleistocene loess deposits, have been truncated by both natural and anthropogenic processes. This study compares the luvisol profiles along a catena / toposequence in a dry valley where a colluvial deposit record is observed. The latter is associated with an intense truncation of luvisols dating from the end of the Protohistoric period, especially during the Late Iron Age (La Tène period, 3rd century BCE), and during a Roman rural occupation (until the Later Roman Empire). Grain-size analysis and geochemistry allow characterizing the nature of colluvium and determine the signature as well as the sediment sourcing. The micromorphological analysis reveals the natural and anthropogenic processes at the origin of the studied microfacies (e.g., soil crusting, waterlogging, cultivation practices). The chronostratigraphy of the sequence is based on AMS 14C dating and archaeological remains, such as a fragment of a rotating grinding wheel from the La Tène period, providing a well-dated terminus post quem (TPQ). The colluviation has increased in modern times, probably due to a combination of both land use, as the main forcing factor, and the Little Ice Age (the LIA occurred approximately between 1550 and 1850 CE) as a secondary factor. The data enable us to reconstruct the diachronic evolution of the settlement over the past 2500 years. They also show the rhythmicity of erosional processes over the course of this period, linked with human and climate forcings.

Notes from the Icehouse: Mixed Methods, Dry Valleys, New Insights

Notes from the Icehouse: Mixed Methods, Dry Valleys, New Insights

Impact of meltwater flow intensity on the spatiotemporal heterogeneity of microbial mats in the McMurdo Dry Valleys, Antarctica

The meltwater streams of the McMurdo Dry Valleys are hot spots of biological diversity in the climate-sensitive polar desert landscape. Microbial mats, largely comprised of cyanobacteria, dominate the streams which flow for a brief window of time (~10 weeks) over the austral summer. These communities, critical to nutrient and carbon cycling, display previously uncharacterized patterns of rapid destabilization and recovery upon exposure to variable and physiologically detrimental conditions. Here, we characterize changes in biodiversity, transcriptional responses and activity of microbial mats in response to hydrological disturbance over spatiotemporal gradients. While diverse metabolic strategies persist between marginal mats and main channel mats, data collected from 4 time points during the austral summer revealed a homogenization of the mat communities during the mid-season peak meltwater flow, directly influencing the biogeochemical roles of this stream ecosystem. Gene expression pattern analyses identified strong functional sensitivities of nitrogen-fixing marginal mats to changes in hydrological activities. Stress response markers detailed the environmental challenges of each microhabitat and the molecular mechanisms underpinning survival in a polar desert ecosystem at the forefront of climate change. At mid and end points in the flow cycle, mobile genetic elements were upregulated across all mat types indicating high degrees of genome evolvability and transcriptional synchronies. Additionally, we identified novel antifreeze activity in the stream microbial mats indicating the presence of ice-binding proteins (IBPs). Cumulatively, these data provide a new view of active intra-stream diversity, biotic interactions and alterations in ecosystem function over a high-flow hydrological regime.

Petrogypsic paleosols on Mars

Unlike the water planet Earth, or furnace planet Venus, Mars is a frigid soil planet, most like the Dry Valleys of Antarctica, which also has paleosols revealing a different past. This study examined rocks in early Amazonian (3000 Ma) sequences of western Candor Chasma, cemented by sulfates and iron oxides. Mars Reconnaissance Orbiter data were used to quantify elevations, and the gypsic bands proved to follow ancient dune surfaces, like petrogypsic horizons of soils. Hesperian-early Amazonian (3700-3000 Ma) gypsic paleosols are widespread on Mars, which also has Noachian (3800-4000 Ma) deeply weathered, kaolinitic paleosols. The Archean (3700-3000 Ma) Earth was similar with both gypsic and deeply weathered profiles. Archean fossil microbes and soils on Earth include acid sulfate and deeply weathered soils, but both life and soil diversified afterward on Earth. There is not yet a fossil record on Mars, but the red planet does have acid sulfate and deeply weathered paleosols of geological ages equivalent to Archean on Earth. Unlike Earth however, there is little evidence of later significant soil formation on Mars.

Temperature Response of Metabolic Activity of an Antarctic Nematode.

Because of climate change, the McMurdo Dry Valleys of Antarctica (MCM) have experienced an increase in the frequency and magnitude of summer pulse warming and surface ice and snow melting events. In response to these environmental changes, some nematode species in the MCM have experienced steady population declines over the last three decades, but Plectus murrayi, a mesophilic nematode species, has responded with a steady increase in range and abundance. To determine how P. murrayi responds to increasing temperatures, we measured metabolic heat and CO2 production rates and calculated O2 consumption rates as a function of temperature at 5 °C intervals from 5 to 50 °C. Heat, CO2 production, and O2 consumption rates increase approximately exponentially up to 40 °C, a temperature never experienced in their polar habitat. Metabolic rates decline rapidly above 40 °C and are irreversibly lost at 50 °C due to thermal stress and mortality. Caenorhabditis elegans, a much more widespread nematode that is found in more temperate environments reaches peak metabolic heat rate at just 27 °C, above which it experiences high mortality due to thermal stress. At temperatures from 10 to 40 °C, P. murrayi produces about 6 times more CO2 than the O2 it consumes, a respiratory quotient indicative of either acetogenesis or de novo lipogenesis. No potential acetogenic microbes were identified in the P. murrayi microbiome, suggesting that P. murrayi is producing increased CO2 as a byproduct of de novo lipogenesis. This phenomenon, in conjunction with increased summer temperatures in their polar habitat, will likely lead to increased demand for carbon and subsequent increases in CO2 production, population abundance, and range expansion. If such changes are not concomitant with increased carbon inputs, we predict the MCM soil ecosystems will experience dramatic declines in functional and taxonomic diversity.

Sediment and Particulate 137Cs Budget Studies in Upa River Basin: History, Results, and Prospects

The intensive pollution of vast areas after the Chernobyl accident, especially in the territories of Ukraine, Russia, and Belarus, has not only become a serious environmental issue, but also presents wide methodological opportunities for studying the functioning of natural systems. The proposed work is a generalization of the results of studies on the migration of 137Cs in the runoff of river sediments, which were carried out in the basin of the Upa River for over 30 years after the accident. This basin is one of the most radioactively contaminated and studied in Central Russia. Over the past three decades, under the conditions of the decreasing snowmelt runoff in the spring and reduced share of cultivated land over the post-Soviet period, the intensity of the 137Cs transfer has decreased. The 137Cs deposit losses associated with erosion activities do not exceed a few percent. Most of the mobilized sediments and sediment-associated radionuclides accumulate in dry valleys or artificial reservoirs. With a general reduction in the durations of floods, rivers have become the predominant channels for the transfer of sediment yield and particulate pollutants. The exploration of the vertical distribution of the 137Cs in the accumulative strata makes it possible to identify the changes in the sediment budgets of the rivers and their radioecological consequences.

Soil erosion models verification in a small catchment for different time windows with changing cropland boundary

This paper presents very detailed studies of soil erosion within a small arable catchment located in the centre of the East European Plain. Sediment redistribution was estimated based on soil profile truncation, radiocesium methods and erosion modelling. WaTEM/SEDEM and State Hydrological Institute model were used for the evaluation of soil losses during rainfall and snowmelt, respectively. Evaluation of soil erosion and sediment redeposition was carried out taking into account historical changes in the cropland boundaries. Model estimates of soil losses from arable land are in good agreement with evaluations of erosion rates based on the results field method applications, taking into account the uncertainty of the methods. Erosion modelling made it possible to fairly plausibly estimate the decrease in soil erosion losses by approximately by a third as a result of a small (about 5%) reduction in the area of arable land in the studied catchment. The main disadvantage of applied erosion models were associated with the insufficient accuracy of estimates of the sedimentation volume and location deposition zones, mainly outside the arable land. The simulated net erosion for the entire catchment was underestimated by 3.5–4.5 times compared with field methods. This simulation block must be calibrated taking into account the regional coefficients of sediment transport in the bottoms of the dry valley network.

Antarctic permafrost degassing in Taylor Valley by extensive soil gas investigation

Ongoing studies conducted in northern polar regions reveal that permafrost stability plays a key role in the modern carbon cycle as it potentially stores considerable quantities of greenhouse gases. Rapid and recent warming of the Arctic permafrost is resulting in significant greenhouse gas emissions, both from physical and microbial processes. The potential impact of greenhouse gas release from the Antarctic region has not, to date, been investigated. In Antarctica, the McMurdo Dry Valleys comprise 10 % of the ice-free soil surface areas in Antarctica and like the northern polar regions are also warming albeit at a slower rate.The work presented herein examines a comprehensive sample suite of soil gas (e.g., CO2, CH4 and He) concentrations and CO2 flux measurements conducted in Taylor Valley during austral summer 2019/2020. Analytical results reveal the presence of significant concentrations of CO2, CH4 and He (up to 3.44 vol%, 18,447 ppmv and 6.49 ppmv, respectively) at the base of the active layer. When compared with the few previously obtained measurements, we observe increased CO2 flux rates (estimated CO2 emissions in the study area of 21.6 km2 ≈ 15 tons day−1). We suggest that the gas source is connected with the deep brines migrating from inland (potentially from beneath the Antarctic Ice Sheet) towards the coast beneath the permafrost layer. These data provide a baseline for future investigations aimed at monitoring the changing rate of greenhouse gas emissions from Antarctic permafrost, and the potential origin of gases, as the southern polar region warms.

Genotype-dependent responses of Andean and Coastal quinoa to plant population density for yield and its physiological determinants in Northwest Argentina

Context In quinoa, similar yields are found under a wide range of plant population densities due to its phenotypic plasticity. Aims This study aimed to identify optimal plant population densities for achieving attainable yields, in relation to the most adapted genotype for a given environment. Methods Andean (RQ252 and RQ420) and Coastal (Titicaca and Puno) genotypes were tested at conventional (14 plants/m2) and low (7 plants/m2) plant population densities, in Dry Valley and Highland mega-environments for 2 years. Key results More than 64% of total variation was explained by genotype, location, and interaction effects for grain yield, biomass, and harvest index. For these variables, the genotype × location × plant population density term presented the highest percentage of variation among triple and quadruple interaction terms. In the Highlands, grain yields decreased with plant population density for Andean genotypes (30–40%), in contrast to lower reductions for Coastal genotypes (9–20%). In the Dry Valleys, no effect of plant population density was found for all genotypes. In the Highlands, reductions in biomass and harvest index explained grain yield response, in parallel with increases in small grain percentage of up to 16% when frosts came early, related to uneven maturity at low plant population density. Conclusions Attainable yields in Northwest Argentina were achieved by exploring local adaptation and response to plant population density of Andean genotypes in the Highlands, in contrast to stable yields of Coastal genotypes through locations and plant population densities. Implications Understanding genotype-dependent responses to plant population density according to Northwest Argentina mega-environments can reduce yield gaps in quinoa production and refine breeding strategies.

Evaluation of the Applicability of Three Methods for Climatic Spatial Interpolation in the Hengduan Mountains Region

Abstract An ideal spatial interpolation approach is indispensable for obtaining high-quality gridded climatic data in mountainous regions with scarce observations, particularly for the Hengduan Mountains Region (HMR) with dense longitudinal ranges and gorges. However, there is much controversy about the applicability of thin plate smooth spline (TPSS), cokriging, and inverse distance weighting (IDW) in mountainous regions. Here, we use the daily observations of temperature and precipitation at 125 stations in HMR and its surroundings from 1961 to 2018 and adopt three interpolation methods to map the annual average temperature and precipitation at a resolution of 500 m in HMR. Then, we assess the applicability of three interpolation methods in HMR from the perspectives of interpolation accuracy and effects. The evaluation implies a satisfactory interpolation accuracy of TPSS with the highest correlation and lowest error, whether for temperature (R2 = 0.92, RMSE = 1.2°C) or precipitation (R2 = 0.54, RMSE = 165.9 mm). In addition, the TPSS could better display the temperature (precipitation) gradient along elevation and depict dry valleys’ high-temperature and low-precipitation characteristics. Moreover, the satisfactory interpolation performance of TPSS mainly benefits from the screening of optimal TPSS model that varied primarily with the regional topography feature and meteorological observation density. The uncertainty of gridded climate datasets has become an urgent problem to solve in the complex terrain. This research illustrates the satisfactory applicability of TPSS for climatic spatial interpolation in HMR, providing theoretical support for high-precision interpolation in complex terrain, hopefully improving the regional weather forecasts and disaster warnings.

The surface energy balance during foehn events at Joyce Glacier, McMurdo Dry Valleys, Antarctica

Abstract. The McMurdo Dry Valleys (MDV) are a polar desert, where glacial melt is the main source of water to streams and the ecosystem. Summer air temperatures are typically close to zero, and therefore foehn events can have a large impact on the meltwater production. A 14-month record of automatic weather station (AWS) data on Joyce Glacier is used to force a 1D surface energy balance model to study the impact of foehn events on the energy balance. AWS data and output of the Antarctic Mesoscale Prediction System (AMPS) on a 1.7 km grid are used to detect foehn events at the AWS site. Foehn events at Joyce Glacier occur under the presence of cyclones over the Ross Sea. The location of Joyce Glacier on the leeward side of the Royal Society Range during these synoptic events causes foehn warming through isentropic drawdown. This mechanism differs from the foehn warming through gap flow that was earlier found for other regions in the MDV and highlights the complex interaction of synoptic flow with local topography of the MDV. Shortwave radiation is the primary control on melt at Joyce Glacier, and melt often occurs with subzero air temperatures. During foehn events, melt rates are enhanced, contributing to 23 % of the total annual melt. Foehn winds cause a switch from a diurnal stability regime in the atmospheric surface layer to a continuous energy input from sensible heat flux throughout the day. The sensible heating during foehn, through an increase in turbulent mixing resulting from gustier and warmer wind conditions, is largely compensated for by extra heat losses through sublimation. Melt rates are enhanced through an additional energy surplus from a reduced albedo during foehn.

Dry air valley in the upper troposphere over the eastern Mediterranean-western Tibetan Plateau

Based on AIRS satellite observations and ERA-Interim reanalysis data, we investigated the seasonal evolution of the dry air valley (DAV) in the upper troposphere over regions from the eastern Mediterranean to the western Tibetan Plateau (EM-WTP). We find that monsoon-related descending motion is the main driver for the DAV, and its contribution to the DAV is 61%. The intensity of DAV increases rapidly in June, reaches its maximum in late July and early August, then weakens gradually until it disappears in early October. From May to July, zonal temperature gradient over the Mediterranean Sea increases and the southerly wind in the western South Asia High enhances, resulting in an enhancement of descending motion over the Mediterranean. Meanwhile, the northerly wind and zonal vorticity gradient over south of the Aral Sea strengthen due to the thermal-dynamical effect of the Tibetan-Iranian Plateau, consequently, descending motion over south of the Aral Sea intensifies. From August to September, the descending motion weakens quickly over the Mediterranean but remains nearly steady over south of the Aral Sea. As a result, the east-west water vapor gradient increases over the DAV, and water vapor in the DAV converges horizontally due to the transport of westerlies. Accordingly, the DAV intensity decreases. Apart from the descending motion, the dry air intrusion from the lower stratosphere associated with tropopause fold events also has an impact on the DAV intensity. However, the contribution of the tropopause fold events to the DAV is rather small, no >10%.

Physical Controls on the Hydrology of Perennially Ice‐Covered Lakes, Taylor Valley, Antarctica (1996–2013)

AbstractThe McMurdo Dry Valleys, Antarctica, are a polar desert populated with numerous closed‐watershed, perennially ice‐covered lakes primarily fed by glacial melt. Lake levels have varied by as much as 8 m since 1972 and are currently rising after a decade of decreasing. Precipitation falls as snow, so lake hydrology is dominated by energy available to melt glacier ice and to sublimate lake ice. To understand the energy and hydrologic controls on lake level changes and to explain the variability between neighboring lakes, only a few kilometers apart, we model the hydrology for the three largest lakes in Taylor Valley. We apply a physically based hydrological model that includes a surface energy balance model to estimate glacial melt and lake sublimation to constrain mass fluxes to and from the lakes. Results show that lake levels are very sensitive to small changes in glacier albedo, air temperature, and wind speed. We were able to balance the hydrologic budget in two watersheds using meltwater inflow and sublimation loss from the ice‐covered lake alone. A third watershed, closest to the coast, required additional inflow beyond model uncertainties. We hypothesize a shallow groundwater system within the active layer, fed by dispersed snow patches, contributes 23% of the inflow to this watershed. The lakes are out of equilibrium with the current climate. If the climate of our study period (1996–2013) persists into the future, the lakes will reach equilibrium starting in 2300, with levels 2–17 m higher, depending on the lake, relative to the 2020 level.

Evaluation of climate factors affecting the quality of red huajiao (Zanthoxylum bungeanum maxim.) based on UPLC-MS/MS and MaxEnt model.

Through field investigation, UPLC-MS/MS technology and MaxEnt model were performed to predict the suitable distribution area for red huajiao (Zanthoxylum bungeanum maxim.) in China from 2021s to 2060s, and evaluate the effects of climate factors on the quality of red huajiao. The results demonstrated that mean temperature of the coldest quarter and min temperature of the coldest month were the most important environmental variables influencing red huajiao distribution. Suitable habitats for red huajiao were located mainly in dry and hot valley zone in the Qinba Mountains and the semi-humid and semi-arid areas of the Loess Plateau. The amides contents were higher in high suitability areas, while it was decreased in medium and low suitability areas, and temperature, wind speed and precipitation played a key role in their accumulation. This investigation was of great significance for the planting area optimization, quality control, benefit improvement and industrial development of red huajiao.

Antibiotic resistance genes and taxa analysis from mat and planktonic microbiomes of Antarctic perennial ice-covered Lake Fryxell and Lake Bonney

AbstractThe perennial ice-covered lakes of the Antarctic McMurdo Dry Valleys harbour oligotrophic microbial communities that are separated geographically from other aquatic systems. Their microbiomes include planktonic microbes as well as lift-off mat communities that emerge from the ice. We used the ShortBRED protein family profiler to quantify the antibiotic resistance genes (ARGs) from metagenomes of lift-off mats emerging from ice and from filtered water samples of Lake Fryxell and Lake Bonney. The overall proportion of ARG hits was similar to that found in temperate-zone rural ponds with moderate human inputs. Specific ARGs showed distinct distributions for the two lakes and for mat vs planktonic sources. Metagenomic taxa distributions showed that mat phototrophs consisted mainly of cyanobacteria or Betaproteobacteria, whereas the water column phototrophs were mainly protists. An enrichment culture of the Betaproteobacterium Rhodoferax antarcticus from a Lake Fryxell mat sample showed an unusual mat-forming phenotype not previously reported for this species. Its genome showed no ARGs associated with Betaproteobacteria but had ARGs consistent with a minor Pseudomonas component. The Antarctic lake mats and water showed specific ARGs distinctive to the mat and water sources, but overall ARG levels were similar to those of temperate water bodies with moderate human inputs.

Survival, metabolic activity, and ultrastructural damages of Antarctic black fungus in perchlorates media.

Evidence from recent Mars landers identified the presence of perchlorates salts at 1 wt % in regolith and their widespread distribution on the Martian surface that has been hypothesized as a critical chemical hazard for putative life forms. However, the hypersaline environment may also potentially preserve life and its biomolecules over geological timescales. The high concentration of natural perchlorates is scarcely reported on Earth. The presence of perchlorates in soil and ice has been recorded in some extreme environments including the McMurdo Dry Valleys in Antarctica, one of the best terrestrial analogues for Mars. In the frame of "Life in space" Italian astrobiology project, the polyextremophilic black fungus Cryomyces antarcticus, a eukaryotic test organism isolated from the Antarctic cryptoendolithic communities, has been tested for its resistance, when grown on different hypersaline substrata. In addition, C. antarcticus was grown on Martian relevant perchlorate medium (0.4 wt% of Mg(ClO4)2 and 0.6 wt% of Ca(ClO4)2) to investigate the possibility for the fungus to survive in Martian environment. Here, the results indicate a good survivability and metabolic activity recovery of the black fungus when grown on four Martian relevant perchlorates. A low percentage of damaged cellular membranes have been found, confirming the ultrastructural investigation.

Latitudinal patterns of particulate and mineral-associated organic matter down the soil profile in drylands

Understanding the controls on particulate organic matter (POM) and mineral-associated organic matter (MAOM) accumulation is essential in order to accurately predict carbon-climate feedbacks and for ecosystem management. However, how POM and MAOM fractions vary across latitudinal gradients in dryland ecosystems, and what drives this variation remains unclear. In this study, we sampled soils from 100 natural shrubland sites across a latitudinal gradient (23°N to 32°N) in the dry valleys of southwestern China to identify latitudinal patterns of POM and MAOM fractions at four soil depths (0–10 cm, 10–20 cm, 20–30 cm, and 30–50 cm). We found that both C and N fractions in POM and MAOM exhibited a binomial trend with latitude at all depths, whereas the N fractions in POM and MAOM exhibited a pronounced increase at higher latitudes in subsurface soils (20–30 cm and 30–50 cm). Variation in C fractions (i.e., particulate organic carbon (POC) and mineral-associated organic carbon (MAOC)) were mainly explained by the independent effect of soil properties, with the most important explanatory factor being exchangeable calcium. In contrast, variation in N fractions (i.e., particulate organic nitrogen (PON) and mineral-associated organic nitrogen (MAON)) were largely explained by interactions between soil , climate and vegetation properties, with the most important driver being mean annual temperature and mean annual precipitation for PON, exchangeable calcium for MAON at 0–10 cm and 10–20 cm depths, and mean annual temperature for MAON at 20–30 cm and 30–50 cm soil depths. Interestingly, climate was more important in explaining variation in C and N fractions in the subsurface soils, and climate and vegetation properties had higher predictive power for soil N fractions than C fractions in the subsurface soils. These results advance our understanding of the role of soil properties on SOM accumulation in dryland ecosystems. Our study also highlights the important impact of climate and vegetation properties in explaining the spatial variation of SOM in subsurface soils, which should be incorporated into large-scale assessments to better predict SOM dynamics.

The hydrogeological karstic chalk system of the Yport springs (Seine-Maritime, France): investigations and resource exploitation

Abstract The small town of Yport in the northern part of the Pays de Caux, Normandy, is located on the shore of the English Channel between Étretat and Fécamp, at the outlet of a long dry valley that incises the chalk plateau. Eight hundred metres to the east, at the base of a cliff, is a cluster of springs, the ‘Fontaines d'Yport’, that emerge on the foreshore. Given their high discharge, measured at between 1 and 2.5 m 3 s −1 , the Le Havre authorities have been interested in these springs since the 1960s, in determining their origin, locating the karst conduit, developing them, and investigating the boundaries and vulnerability of the groundwater basin. Today, one third of the drinking water that supplies the Le Havre conurbation comes from the Yport wells, and investigations into their vulnerability and protection of their resource continues.