Dry Valleys Research Articles

Land Suitability Evaluation of Sorghum Planting in Luquan County of Jinsha River Dry and Hot Valley Based on the Perspective of Sustainable Development of Characteristic Poverty Alleviation Industry

Land suitability evaluation is the basis for optimizing and adjusting regional land use structure and layout, making scientific decisions, and planning, according to local conditions. It is also the basis for developing local characteristic poverty alleviation industries, and achieving sustainable development according to local conditions. However, existing research on the evaluation of land suitability rarely results in scientifically selecting the land resource area of a single crop, based on the principle of “suitable planting in the right place” and “suitable growth in the right place”; additionally, it does not conduct the land suitability evaluation of a single crop from the perspective of the sustainable development of the characteristic poverty alleviation industry. As the evaluation scope, this paper takes the dry and hot valley area of the Jinsha River, in Luquan County, Yunnan Province, as an example, selects eight evaluation factors, and organically combines the “limit condition method” and the “suitability index method”, determining 27,877.59 hectares of irrigated land, dry land, and other grasslands, below 1800 m above sea level in Luquan County in the Jinsha River basin. According to the principles of “suitable planting in the right place” and “suitable growth in the right place”, the suitability of sorghum planting land was evaluated. The evaluation results show that: the land area suitable for planting sorghum is 24,227.61 hectares, accounting for 86.91%. The area of land unsuitable for planting is 3649.98 hectares, and the area with a gradient over 25°, and obvious water and soil loss, accounts for 51.68% of the area of land being unsuitable for planting. The area of land unsuitable for planting is 48.32%, due to the restriction of soil thickness, soil texture, and bare rock, etc. The land that is not suitable for planting sorghum needs to be included in the scope of ecological protection. Compared with the 1200 hectares that have been developed and planted at present, there are still sufficient land resources suitable for planting sorghum. However, the area and proportion of land suitable for planting sorghum in different townships are quite different, so it is necessary to make a reasonable layout of the land suitable for planting sorghum according to local conditions. Among the land suitable for sorghum planting in the county, the proportion of the first, second, and third grade land suitable for sorghum planting is about 14:35:51. This shows that the area of first-class land suitable for planting is relatively small. This is because the terrain of the Jinsha River basin is characterized by: high mountains, steep slopes, deep valleys, little flat land, mainly mountains, shallow soil layers on slopes, and has poor texture. Therefore, there are many third-class suitable lands for planting with poor quality, and many reconstruction measures need to be taken to improve the quality of land suitable for planting.

Timing and duration of ephemeral Antarctic water tracks and wetlands using high temporal–resolution satellite imagery, high spatial–resolution satellite imagery, and ground-based sensors in the McMurdo Dry Valleys

ABSTRACT Antarctic water tracks and ephemeral wetlands are a primary location for biogeochemical soil processes driving cold desert soil formation. Though the spatial extent of water tracks and wetted soils has been mapped in the McMurdo Dry Valleys (MDV) on the basis of mapping darkened pixels in high-resolution commercial satellite imagery, the timescale over which water tracks and wetlands form and the duration of these biogeochemically active environments remain unknown. Here, we determine the start date and end dates and the duration of wetted soils at ten sites located across the MDV using a combination of in situ soil sensors and two complementary remote imaging platforms (Planet and WorldView) to understand the hydroclimatic processes that drive water track and wetland formation. Our remote sensing employs a terrain correction workflow that removes the contribution of differential direct illumination and small-scale shadowing on pixel brightness, reducing false positives (soils identified as wetted when in fact they are shadowed or darkened as a consequence of high phase angle). Our findings extend the water track and wetland hydroperiod by over a month, showing darkening occurring from November to March, suggesting hydrological contributions from ground ice thaw, snowmelt, and salt deliquescence and soil brine growth.

Changes in the characteristics of flood discharge and sediment yield in a typical watershed in the Hengduan Mountain Region, Southwest China, under extreme precipitation events

Precipitation extremes can pose adverse impacts on local and downstream society, economy, and ecosystems. Accordingly, their characteristics have attracted widespread attention in many regions, such as the world famous Hengduan Mountain Region in Southwest China, where the overall characteristics in precipitation extremes have been widely reported yet. However, the spatial heterogeneity and internal variation of precipitation extremes caused by the complicated topography were rarely reported, moreover, few studies have evaluated the effect of dynamics in precipitation extremes and soil and water conservation measures on changes in flood discharge and sediment yield. In this study, a typical watershed in the Hengduan Mountain Region, the Longchuanjiang watershed, was selected to identify the dynamics in precipitation extremes from 1965 to 2018, and the contributions of soil and water conservation measures on the characteristics in flood discharge and sediment load. The results of this study are as follows. 1) Substantial decreasing trends occurred for both flood discharge and sediment yield from the early period (1965–2008) to the later period (2009–2018) in the Longchuanjiang watershed. 2) The increase in precipitation extremes in the dry-hot valley and decrease in the mountains revealed great internal variation of the characteristics in precipitation extremes in the Longchuanjiang watershed.3) Soil and water conservation measures that were implemented in recent decades, such as terraced farmland, forest and grass plantation, ecological restoration, and small reservoirs, resulted in the significant reduction of both flood discharge and sediment yield under similar extreme precipitation events. This study highlights the discrepancy of dynamics in precipitation extremes in the dry valleys with an entire watershed in the Hengduan Mountain Region, emphasizes the risks of soil erosion in the ecologically fragile dry valley, and assesses the contribution of soil and water conservation measures on changes in characteristics of flood discharge and sediment load in the selected watershed. The study results are of great importance not only for gaining a scientific understanding of changes in precipitation extremes, flood discharge, and sediment yield but also for the objective assessment of the ecological benefits of soil and water conservation projects and deployment of suitable measures in the future.

The South Asian monsoon maintains the disjunction of Rumex hastatus between the western Himalayas and the Hengduan Mountains, southwest China

The Himalayas and the Hengduan Mountains of southwest China are hotspots of both climatic and species diversity. Yet, the distribution patterns of semi‐arid plant communities that have arisen throughout the region's complex uplift history remain insufficiently understood. In particular, the striking disjunctions of plants associated with dry river valleys that solely occur on the eastern and western ends of the Himalayan arc, but are absent in between, lack a sound explanation. Here we aim to disentangle the more recent environmental drivers behind the disjunction of the semi‐woody shrub Rumex hastatus found in dry river valleys of the western Himalayas and the Hengduan Mountains. We used ecological niche modeling and enhanced random forest parameterizations (down‐sampling) to infer suitable and unsuitable habitats within the study area during the last glacial maximum, under present climate conditions, and under four future climate scenarios. Annual and seasonal precipitation contributed the strongest to the discrimination between occurrences and the distribution gap, with the latter showing much higher rainfall amounts. The gap was also characterized by low overall habitat suitability, whereas occurrence probabilities in dry river valleys inhabited by R. hastatus were very high. However, some suitable but isolated habitats within the gap were detected in Bhutan and the southeastern Tibetan Plateau. The identified distribution gap was consistent in all simulated scenarios from the last glacial maximum to the near future. Our results suggest that the South Asian summer monsoon system acts as a persistent ecological barrier maintaining the disjunct distribution of dry river valley‐dwelling plants in the western Himalayas and the Hengduan Mountains.

BOVEDA, the Bolivian Vegetation Ecology Database: first stage, the Chacoan forests

Bolivia is a country exceptionally rich in biodiversity and home to about 20,000 vascular plant species and 15 plant formations. Therefore, it is particularly important to document the biodiversity of this territory. The aim of the Bolivian Vegetation Ecology Database (BOVEDA; GIVD ID SA-BO-005) is to record floristic and ecological data of Bolivian vegetation. In the first stage, the database hosts 320 relevés from one of the most unique biogeographical units in the country, the Chaco. In total, 633 species belonging to 114 families have been recorded. Data on vegetation structure, soil, flooding regime and geomorphology have also been stored. The following nine vegetation structural types were identified: (1) deciduous forests of alluvial plains on well to moderately well drained soils; (2) deciduous to semideciduous Chaco forests transitional to the Andes; (3) deciduous and sclerophyllous Cerrado thorn-woodlands and shrublands transitional to the Chaco (Abayoy); (4) xeromorphic thorn shrubland and thickets on vertic, poorly drained soils; (5) woodlands and savannas on sand dunes and aeolian surfaces; (6) freshwater swamp forests; (7) saltwater swamp forests; (8) phreatophytic forests; (9) deciduous to semideciduous Chaco forests transitional to the Chiquitania. Further steps will be to incorporate new types of vegetation already recorded in the field such as Altiplano shrublands, Andean wetlands, Andean Polylepis forests, and vegetation of the dry inter-Andean valleys. Taxonomic reference: Jørgensen et al. (2015). Abbreviations: BOVEDA = Bolivian Vegetation Ecology Database; GIVD = Global Index of Vegetation-Plot Databases.

The spatial distribution and biogeochemical drivers of nitrogen cycle genes in an Antarctic desert

Antarctic deserts, such as the McMurdo Dry Valleys (MDV), represent extremely cold and dry environments. Consequently, MDV are suitable for studying the environment limits on the cycling of key elements that are necessary for life, like nitrogen. The spatial distribution and biogeochemical drivers of nitrogen-cycling pathways remain elusive in the Antarctic deserts because most studies focus on specific nitrogen-cycling genes and/or organisms. In this study, we analyzed metagenome and relevant environmental data of 32 MDV soils to generate a complete picture of the nitrogen-cycling potential in MDV microbial communities and advance our knowledge of the complexity and distribution of nitrogen biogeochemistry in these harsh environments. We found evidence of nitrogen-cycling genes potentially capable of fully oxidizing and reducing molecular nitrogen, despite the inhospitable conditions of MDV. Strong positive correlations were identified between genes involved in nitrogen cycling. Clear relationships between nitrogen-cycling pathways and environmental parameters also indicate abiotic and biotic variables, like pH, water availability, and biological complexity that collectively impose limits on the distribution of nitrogen-cycling genes. Accordingly, the spatial distribution of nitrogen-cycling genes was more concentrated near the lakes and glaciers. Association rules revealed non-linear correlations between complex combinations of environmental variables and nitrogen-cycling genes. Association rules for the presence of denitrification genes presented a distinct combination of environmental variables from the remaining nitrogen-cycling genes. This study contributes to an integrative picture of the nitrogen-cycling potential in MDV.

Glacial Legacies: Microbial Communities of Antarctic Refugia.

Simple SummaryMicrobial communities in Antarctica have only recently been described with the increasing popularity and ease of genome sequencing. Using these methods, we aimed to test hypotheses of refugia using microbial communities in the McMurdo Dry Valleys of Victoria Land, Antarctica. Refugia are habitable areas that remain undisturbed during cycles of glacial expansions throughout Earth’s history. They may contain ancient lineages and unique communities worthy of conservation, as well as provide insight into the biotic history of Antarctica. We found unique microbial community assemblages from putative refugia in the McMurdo Dry Valleys indicating long-lived climax-communities in one of the harshest environments in the world. This finding corroborates the importance of glacial legacies in structuring not just the physical and geochemical environment, but also the soil microbial communities in this landscape.In the cold deserts of the McMurdo Dry Valleys (MDV) the suitability of soil for microbial life is determined by both contemporary processes and legacy effects. Climatic changes and accompanying glacial activity have caused local extinctions and lasting geochemical changes to parts of these soil ecosystems over several million years, while areas of refugia may have escaped these disturbances and existed under relatively stable conditions. This study describes the impact of historical glacial and lacustrine disturbance events on microbial communities across the MDV to investigate how this divergent disturbance history influenced the structuring of microbial communities across this otherwise very stable ecosystem. Soil bacterial communities from 17 sites representing either putative refugia or sites disturbed during the Last Glacial Maximum (LGM) (22-17 kya) were characterized using 16 S metabarcoding. Regardless of geographic distance, several putative refugia sites at elevations above 600 m displayed highly similar microbial communities. At a regional scale, community composition was found to be influenced by elevation and geographic proximity more so than soil geochemical properties. These results suggest that despite the extreme conditions, diverse microbial communities exist in these putative refugia that have presumably remained undisturbed at least through the LGM. We suggest that similarities in microbial communities can be interpreted as evidence for historical climate legacies on an ecosystem-wide scale.

Complex dynamics of twig elements and stoichiometric ratios with altitude changes in the typical dry valley, eastern Qinghai-Tibet plateau

The concentrations of carbon (C), nitrogen (N), phosphorus (P) and stoichiometric ratios of twig (i.e. stem and leaves) are the important indicators to connect plant individual and the abiotic environment, which reflects the nutritional status for plants and ecosystem function. However, the variations of stoichiometric characteristics of twig C, N and P across altitude gradient have not yet been extensively studied. In the present study, we determined the elements (C, N and P) concentrations of current-year twigs from 1050 to 3070 m woody plants in the Bailongjiang River Basin (BRB), a typical dry valley of eastern Qinghai-Tibet plateau. And then, the relationships between altitude and the element concentrations of twigs, stems, and leaves had been explored by linear regression, allometric analysis and phylogenetic analysis. The results showed that: the frequency distribution of elemental concentrations and stoichiometric ratios was left-deviations. The C, N and P concentrations were 395.66 mg g−1, 17.59 mg g−1 and 1.53 mg g−1 for leaves, 414.83 mg g−1, 8.76 mg g−1 and 1.13 mg g−1 for stems, and 401.72 mg g−1, 8.78 mg g−1 and 1.51 mg g−1 for twigs, respectively. The stems elemental concentrations and stoichiometric ratios were positively correlated to that of the leaves. Except for the N of stem and twig, the other elemental concentrations were significantly correlated to altitude. And the leaves and stems N/P and C/P, and twig C/P were significantly negative correlated to altitude. The significant isometry relationships were observed between N vs P of leaves, stems and twigs. The elemental concentrations and stoichiometric ratios of BRB woody plant had no statistical phylogenetic signal. This study presented the evidence that the leaf, stem and twig C, N and P concentrations and stoichiometric ratios from wider altitude-gradient within BRB, it was special and varied largely in different elements, stoichiometric ratios and locations, which supported the growth rate theory in the whole.

Summer bird populations of burnt bog-forest land of the Kerzhensky Nature Reserve ten years after wildfires (Central Volga region, Russia)

The bird population was monitored during ten years in the Kerzhensky Nature Reserve damaged by severe wildfires in 2010. In the burned territory 126 bird species (120 species in the breeding season) were noted, for which weighted averages of bird abundance were calculated. It was noted that the number of species was increasing gradually in the breeding season. The birds of forest edges and of dry valleys appeared already during the second post-fire year, but their abundance increased only in the third-fourth year. The bird population abundance has increased almost 2 times in the breeding season over ten years, while it has not increased significantly in the post-breeding season. The total biomass and the transformed energy, on the contrary, decreased especially in the post-breeding season. During the first six years Fringilla coelebs Linnaeus, 1758 was the absolute leader at the abundance, and its co-dominant was Anthus trivialis (Linnaeus, 1758), and in last two years Phylloscopus trochilus (Linnaeus, 1758) was the leader. The share of the leaders in the breeding season gradually decreased, and the species diversity and the alignment grew. The birds fed in the breeding season mostly on the soil surface. The share of shrubby species increased by two times a couple of years after the wildfires, and the share of crowns birds increased after another four years. The similarity of the ornithocomplex of the burnt territory in the first and last two years of the research amounted to only 0.63 units (the Sorensen-Chekanovsky index).

Mastigostyla moqueguensis (Tigridieae: Iridaceae), a new species from southern Peru

A new species, Mastigostyla moqueguensis Huaylla & Llalla, is described from the Andes of Moquegua in southern Peru. Mastigostyla, which belongs to the tribe Tigridieae, is widely distributed in the Puna and Andean dry valleys of southern Peru and central Bolivia. The new species can be recognized by its ovate-lanceolate, acute inner tepals with glands at the base. It shows some affnity with M. torotoroensis because of the fliform, bifid style arms with apical stigmas. We present photographs and a table highlighting differences between the new specie and some similar species.

Using Geochemical and Environmental Isotopic Tracers to Evaluate Groundwater Recharge and Mineralization Processes in Qena Basin, Eastern Nile Valley, Egypt

The Qena basin (16,000 km2) represents one of the largest dry valleys located in the arid Eastern Desert of Egypt. Groundwater resources in this watershed are scarce due to limited recharge from annual precipitation. Hydrogeochemistry and environmentally stable isotopes were utilized to determine the main sources of recharge and geochemical processes affecting groundwater quality. The studied basin comprises three main groundwater aquifers: the Quaternary aquifer, the Post-Nubian aquifer (PNA) of the Paleocene-Eocene age, and the Nubian Sandstone aquifer (NSA) of the Lower Cretaceous age. Groundwater types vary from fresh to brackish groundwater. The groundwater salinity of the Quaternary aquifer ranges from 426 to 9975 mg/L with an average of 3191 mg/L, the PNA’s groundwater salinity ranges from 1134 to 6969 mg/L with an average of 3760 mg/L, and the NSA’s groundwater salinity ranges from 1663 to 1737 mg/L with an average of 1692 mg/L. The NSA’s groundwater is relatively depleted of stable isotopes’ signatures (ranges: δ18O from −9‰ to −4.81‰; δ2H from −71‰ to −33.22‰), whereas the Quaternary aquifer’s groundwater is relatively enriched (ranges: δ18O from −5.51 to +4.70‰; δ2H from −40.87 to +37.10‰). Geochemical and isotopic investigations reveal that the NSA groundwater is a paleo-water recharged in a cooler climate. In contrast, the upstream Quaternary groundwater receives considerable recharge from recent meteoric water and upward leakage from the artesian NSA. The downstream Quaternary aquifer in the delta of the Qena basin is composed of original groundwater mixed with recharge from the River Nile. Isotopic analysis confirms that the PNA’s groundwater recharge (ranges: δ18O from −5.90 to −0.10; δ2H −58.21 to −7.10‰) mainly originates from upward leakage from the NSA under the artesian condition and seepage from the upper unconfined Quaternary aquifer. NETPATH geochemical model results show that water–rock interaction, evaporation, and mixing are the main geochemical and physical processes controlling the groundwater quality. NSA groundwater has a significant regional extension and salinity suitable for use in expanding agricultural projects; it should be well managed for sustainable development.

Isotopic signature of massive, buried ice in eastern Taylor Valley, Antarctica: Implications for its origin

ABSTRACT The coastal regions of the McMurdo Dry Valleys, Antarctica, contain deposits of the Ross Sea Drift, sedimentary material left from the Ross Sea ice sheet from the advance of the West Antarctic ice sheet during the Last Glacial Maximum. Much of this deposit is ice-cored, but data on the stable isotopic composition of water from this ice, which may contain a valuable climate archive, are sparse or incomplete. Widespread thermokarstic ground subsidence in this “coastal thaw zone” of the McMurdo Dry Valleys suggests that these potential records are rapidly being lost due to the melting of ground ice and permafrost. We collected samples of massive buried ice from the Ross Sea Drift in eastern Taylor Valley for δ18O-H2O and δ2H-H2O and measured a broad range of values (δ18O = −27.7 to −37.3 ‰; δ2H = −210 to −295 ‰). These buried ice deposits do not show evidence of alteration through sublimation or evaporation, plot along the local meteoric water line, and have values that indicate ice deposition under a colder climate than present conditions. We propose that this ice was sourced from the Ross Sea ice sheet during the Last Glacial Maximum and contains a valuable and accessible climate record.

The Characteristics of Soil Ca and Mg Leakage in a Karst Depression

The soil leakage characteristics of depressions in karst areas should be explored by investigating their soil Ca and Mg contents. As a starting point, in a karst landform typical of Guizhou Huajiang dry valley karst watersheds, we selected surface depression and performed a field investigation, soil profile excavation, and soil sample collection. The soil samples were pretreated and taken to the laboratory for soil physical and chemical analysis. The data were processed, and the Ca and Mg contents of the soils were analyzed to determine the spatial variation characteristics of soil leakage in the depression. We found that in the depression watershed, the Ca and Mg contents in the 0–30 cm soil profile generally increased with increasing soil depth, and the Ca and Mg contents in the 30–150 cm soil profile exhibited more variability with increasing soil depth. The Ca and Mg in the soil surface profiles from the top of the slope, middle of the slope, base of the slope, bottom of the depression, and sinkhole showed obvious characteristics of a sedimentary soil leakage migration path. In combination with analyses of the soil K and N contents, the soil Ca and Mg contents can be used as an index of the likelihood of soil and water leakage in karst depressions.

A shallow salt pond analog for aqueous alteration on ancient Mars: Spectroscopy, mineralogy, and geochemistry of sediments from Antarctica’s Dry Valleys

Abstract Understanding past and present aqueous activity on Mars is critical to constraining martian aqueous geochemistry and habitability, and to searching for life on Mars. Assemblages of minerals observed at or near the martian surface include phyllosilicates, sulfates, iron oxides/hydroxides, and chlorides, all of which are indicative of a complex history of aqueous activity and alteration in the martian past. Furthermore, features observed on parts of the martian surface suggest present-day activity of subsurface brines and at least transient liquid water. Terrestrial analogs for younger and colder (Hesperian–Amazonian) martian geologic and climatic conditions are available in the McMurdo Dry Valleys (MDV) of Antarctica and provide opportunities for improved understanding of more recent aqueous activity on Mars. Here, we study the VXE-6 intermittent brine pond site from Wright Valley in the MDV region and use coordinated spectroscopy, X-ray diffraction, and elemental analyses to characterize the mineralogy and chemistry of surface sediments that have evolved in response to aqueous activity at this site. We find that brine pond activity results in mineral assemblages akin to aqueous alteration products associated with younger sites on Mars. In particular, surficial chlorides, a transition layer of poorly crystalline aluminosilicates and iron oxides/hydroxides, and a deeper gypsum-rich interval within the upper 10 cm of sediment are closely related at this Antarctic brine pond site. Activity of the Antarctic brine pond and associated mineral formation presents a process analog for chemical alteration on the martian surface during episodes of transient liquid water activity during the late Hesperian and/or more recently. Our results provide a relevant example of how aqueous activity in a cold and dry Mars-like climate may explain the co-occurrence of chlorides, clays, iron oxides/hydroxides, and sulfates observed on Mars.

Altitudinal Variation Influences Soil Fungal Community Composition and Diversity in Alpine-Gorge Region on the Eastern Qinghai-Tibetan Plateau.

Soil fungi play an integral and essential role in maintaining soil ecosystem functions. The understanding of altitude variations and their drivers of soil fungal community composition and diversity remains relatively unclear. Mountains provide an open, natural platform for studying how the soil fungal community responds to climatic variability at a short altitude distance. Using the Illumina MiSeq high-throughput sequencing technique, we examined soil fungal community composition and diversity among seven vegetation types (dry valley shrub, valley-mountain ecotone broadleaved mixed forest, subalpine broadleaved mixed forest, subalpine coniferous-broadleaved mixed forest, subalpine coniferous forest, alpine shrub meadow, alpine meadow) along a 2582 m altitude gradient in the alpine–gorge region on the eastern Qinghai–Tibetan Plateau. Ascomycota (47.72%), Basidiomycota (36.58%), and Mortierellomycota (12.14%) were the top three soil fungal dominant phyla in all samples. Soil fungal community composition differed significantly among the seven vegetation types along altitude gradients. The α-diversity of soil total fungi and symbiotic fungi had a distinct hollow pattern, while saprophytic fungi and pathogenic fungi showed no obvious pattern along altitude gradients. The β-diversity of soil total fungi, symbiotic fungi, saprophytic fungi, and pathogenic fungi was derived mainly from species turnover processes and exhibited a significant altitude distance-decay pattern. Soil properties explained 31.27−34.91% of variation in soil fungal (total and trophic modes) community composition along altitude gradients, and the effects of soil nutrients on fungal community composition varied by trophic modes. Soil pH was the main factor affecting α-diversity of soil fungi along altitude gradients. The β-diversity and turnover components of soil total fungi and saprophytic fungi were affected by soil properties and geographic distance, while those of symbiotic fungi and pathogenic fungi were affected only by soil properties. This study deepens our knowledge regarding altitude variations and their drivers of soil fungal community composition and diversity, and confirms that the effects of soil properties on soil fungal community composition and diversity vary by trophic modes along altitude gradients in the alpine–gorge region.

Drone-based investigation of natural restoration of vegetation in the water level fluctuation zone of cascade reservoirs in Jinsha River

The reservoir water level fluctuation zone (WLFZ) is a new and fragile ecosystem that is gaining attention with the construction of large and medium-sized hydropower plants. Compared to the natural riparian zone, it has a greater drop in water level, longer inundation time, more intense impact from alternating wet and dry conditions, and a wider impact on ecological security. The Jinsha River basin is located in the upper reaches of the Yangtze River in China, and several world-class large-scale hydropower projects with dam heights over 100 m have been built, forming a large area of reservoir WLFZ, however, due to the short time since their construction, there are few related studies. In this paper, fixed sample plots were set up in the typical WLFZs of each large reservoir in the Jinsha River basin. In response to the problem of the precipitous terrain and poor accessibility of the Jinsha River basin, a combination of small UAV surveys and field research in July 2020 was used to draw vegetation cover maps and extract topographic data for each site, and quantitatively analyse the community composition, dominant species types, area, coverage, spatial distribution patterns and environmental factors of tolerant vegetation using spatial superposition analysis, neural network models, landscape pattern indices and typical correlation analysis. The results showed that the original drought-tolerant vegetation in the arid river valley WLFZ has evolved into amphibious herbaceous vegetation, with trees and shrubs disappearing and species composition tending to be simpler. 44 species of plants, mainly in the Asteraceae and Gramineae families, were extant, 61% of which were also reported in the Three Gorges Reservoir WLFZ. The water level variation showed convergence in the natural screening process of suitable species in the WLFZ. Moreover, even in the dry valley WLFZs, flood stress showed a more significant filtering effect on vegetation species than drought stress. The vegetation in the WLFZ showed an obvious band-like aggregated distribution along the water level elevation gradient, and the vegetation coverage along the flooding gradient is as follows: upper part of the WLFZ >> middle part > lower part, and mainly concentrated in the gentle area with slope less than 35°. Flooding stress, drought stress and soil substrate deficiency were the main limiting factors for vegetation recovery in the WLFZ. The vegetation restoration of the WLFZ should be adapted to local conditions, and the dominant role of native species should be emphasized. At the early stage of the restoration of the WLFZ, native species should be selected for artificial planting to accelerate the formation of vegetation cover, and gradually advance downwards along the gradient of water level elevation, while for areas of the WLFZ with slopes greater than 35° and large topographic relief, biological engineering measures should be used to help plant establishment, and after a certain stable cover has been formed, natural restoration should be the main focus.

Addendum to Diercks et al., 2021: A model for the formation of the Pradol (Pradolino) dry valley in W Slovenia and NE Italy

In our paper Diercks et al. (2021) we presented geomorphological data and field observations from W Slovenia and NE Italy to develop a model for the formation of the Pradolino (slov. Pradol) dry valley. After publication we were kindly pointed to existing studies on the area that we were unaware of. To fill that gap and to properly credit previous work, in this addendum we summarise the research history on the study area and briefly compare earlier views with our model.

Antarctic lake phytoplankton and bacteria from near-surface waters exhibit high sensitivity to climate-driven disturbance.

The McMurdo Dry Valleys (MDVs), Antarctica, represent a cold, desert ecosystem poised on the threshold of melting and freezing water. The MDVs have experienced dramatic signs of climatic change, most notably a warm austral summer in 2001-2002 that caused widespread flooding, partial ice cover loss and lake level rise. To understand the impact of these climatic disturbances on lake microbial communities, we simulated lake level rise and ice-cover loss by transplanting dialysis-bagged communities from selected depths to other locations in the water column or to an open water perimeter moat. Bacteria and eukaryote communities residing in the surface waters (5m) exhibited shifts in community composition when exposed to either disturbance, while microbial communities from below the surface were largely unaffected by the transplant. We also observed an accumulation of labile dissolved organic carbon in the transplanted surface communities. In addition, there were taxa-specific sensitivities: cryptophytes and Actinobacteria were highly sensitive particularly to the moat transplant, while chlorophytes and several bacterial taxa increased in relative abundance or were unaffected. Our results reveal that future climate-driven disturbances will likely undermine the stability and productivity of MDV lake phytoplankton and bacterial communities in the surface waters of this extreme environment.

Study on Relationship between Joint Surface’s Shear Strength and Morphology Parameter Deterioration of Typical Bank Slope in Wudongde

The change of typical bank slope’s water occurrence environment and the special climatic condition of dry hot valley in Wudongde reservoir area will make the shear characteristics of jointed rock mass on bank slope deteriorate continuously. Based on this, the shear test of joint surface under heat-wet cycles is carried out. The results show the following. (1) The shear strength and joint roughness deteriorate significantly with the increasing test cycles, and the deterioration ranges are 70.90%–84.48% and 29.33%–61.56% in the first 5 cycles. (2) The shear strength’s deterioration caused by repeated shear is mainly in the initial state, and the shear strength’s deterioration caused by heat-wet cycles increases firstly and decreases later with the test cycles. (3) By introducing the equivalent damage coefficient of morphology, the shear strength calculation formula is improved, and it can be seen that the estimated value coincides with the modified test value. The research results can provide a reference for long-term variation and calculation method of joint surface’s shear strength under different water-rock interactions.

Dissolved Organic Carbon Chemostasis in Antarctic Polar Desert Streams

AbstractDissolved organic carbon (DOC) is a key variable impacting stream biogeochemical processes. The relationship between DOC concentration (C) and stream discharge (q) can elucidate spatial and temporal DOC source dynamics in watersheds. In the ephemeral glacial meltwater streams of the McMurdo Dry Valleys (MDV), Antarctica, the C‐q relationship has been applied to dissolved inorganic nitrogen and weathering solutes including silica, which all exhibit chemostatic C‐q behavior; but DOC‐q dynamics have not been studied. DOC concentrations here are low compared to temperate streams, in the range of 0.1–2 mg C l−1, and their chemical signal clearly indicates derivation from microbial biomass (benthic mats and hyporheic biofilm). To investigate whether the DOC generation rate from these autochthonous organic matter pools was sufficient to maintain chemostasis for DOC, despite these streams' large diel and interannual fluctuations in discharge, we fit the long‐term DOC‐q data to a power law and an advection‐reaction model. Model outputs and coefficients of variation characterize the DOC‐q relationship as chemostatic for several MDV streams. We propose a conceptual model in which hyporheic carbon storage, hyporheic exchange rates, and net DOC generation rates are key interacting components that enable chemostatic DOC‐q behavior in MDV streams. This model clarifies the role of autochthonous carbon stores in maintaining DOC chemostasis and may be useful for examining these relationships in temperate systems, which typically have larger sources of bioavailable autochthonous organic carbon than MDV streams but where this autochthonous signal could be masked by a stronger allochthonous contribution.