Cyanobacteria and loess-an underestimated interaction

Background: Biocrusts are important functional units in dryland ecosystems. Regarded as ecosystem engineers, cyanobacteria in biocrusts contribute several major physico-chemical and biological processes. However, the role of cyanobacteria in the process of loess formation has been underestimated. Recently, their contribution to sediment development was presented in the BLOCDUST model of loess formation. Scope: This perspective paper features the environmental impact of cyanobacteria and biocrusts with a focus on processes involved in the formation of loess sediments. We propose that the formation of loess can be mediated by cyanobacteria, including initial trapping, and the accumulation and preservation of loess-forming particles. Moreover, the initial structure may be further altered by weak mineral weathering, dissolution and mineral re-precipitation due to cyanobacterial metabolic processes. Possible negative aspects of environmental impact related to the potential toxicity of cyanobacterial biocrusts are also discussed. We highlight specific biotic-abiotic interactions between biocrusts and loess (e.g. exudation of organic polymers, carbonate dissolution and re-precipitation, and dust-dependent metabolic activities of cyanobacteria) which are essential for the formation of stabilized loess and propose the term “synergosis” to comprise these interactions. Conclusion: The role of cyanobacteria in loess formation has only recently been recognized and the possible biogenic nature of loessification is underestimated as compared to their eolian nature. Mineral weathering and mineral precipitation processes as well as mineral dust flux between litho- and atmosphere mediated by cyanobacteria and biocrusts require more attention due to their significant contribution to ecosystem properties

Research on evaporation of Taiyuan basin area by using remote sensing

International audienceTaiyuan basin is enclosed by hills and mountains, located in the middle of Shanxi province, standing between longitudes 111°40'?113°00'E and latitude 37°00'?38&deg00'N. With various types and wide distribution, the mineral resources are very abundant in this basin area. However, there is a great shortage of water resources. Due to continual fall of groundwater level caused by excessive extraction of ground water, some severe environmental problems are induced in this area, such as ground subsidence, etc. The goal of this paper is to estimate the spatial distribution of actual evaporation over the basin by using remote sensing data. The Surface Energy Balance System (SEBS) has been developed (Su, 2001, 2002). Using visible and infrared satellite remote sensing data, SEBS is based on land surface energy balance theory combined with the in-situ meteorological data or the product of atmospheric numerical model to estimate land surface turbulent flux and the relative evaporation at different scales. SEBS was served as the core methodology of this paper and was used for evaporation estimation. On the basis of hydro-geological data and NOAA satellite data, the SEBS was used in this paper for the estimation of actual evaporation of Taiyuan basin. The spatial distribution of the evaporative fraction and daily evaporation over the basin area was shown. On the other hand, the difference of land surface parameters and evaporation for various target types in the basin area was discussed

Modelling the effectiveness of grass buffer strips in managing muddy floods under a changing climate

Muddy floods occur when rainfall generates runoff on agricultural land, detaching and transporting sediment into the surrounding natural and built environment. In the Belgian Loess Belt, muddy floods occur regularly and lead to considerable economic costs associated with damage to property and infrastructure. Mitigation measures designed to manage the problem have been tested in a pilot area within Flanders and were found to be cost-effective within three years. This study assesses whether these mitigation measures will remain effective under a changing climate. To test this, the Water Erosion Prediction Project (WEPP) model was used to examine muddy flooding diagnostics (precipitation, runoff, soil loss and sediment yield) for a case study hillslope in Flanders where grass buffer strips are currently used as a mitigation measure. The model was run for present day conditions and then under 33 future site-specific climate scenarios. These future scenarios were generated from three earth system models driven by four representative concentration pathways and downscaled using quantile mapping and the weather generator CLIGEN. Results reveal that under the majority of future scenarios, muddy flooding diagnostics are projected to increase, mostly as a consequence of large scale precipitation events rather than mean changes. The magnitude of muddy flood events for a given return period is also generally projected to increase. These findings indicate that present day mitigation measures may have a reduced capacity to manage muddy flooding given the changes imposed by a warming climate with an enhanced hydrological cycle. Revisions to the design of existing mitigation measures within existing policy frameworks are considered the most effective way to account for the impacts of climate change in future mitigation planni

Conservation Tillage Increases Water Use Efficiency of Spring Wheat by Optimizing Water Transfer in a Semi-Arid Environment

Water availability is a major constraint for crop production in semiarid environments. The impact of tillage practices on water potential gradient, water transfer resistance, yield, and water use e�ciency (WUEg) of spring wheat was determined on the western Loess Plateau. Six tillage practices implemented in 2001 and their e�ects were determined in 2016 and 2017 including conventional tillage with no straw (T), no-till with straw cover (NTS), no-till with no straw (NT), conventional tillage with straw incorporated (TS), conventional tillage with plastic mulch (TP), and no-till with plastic mulch (NTP). No-till with straw cover, TP, and NTP significantly improved soil water potential at the seedling stage by 42, 47, and 57%, respectively; root water potential at the seedling stage by 34, 35, and 51%, respectively; leaf water potential at the seedling stage by 37, 48, and 42%, respectively; tillering stage by 21, 24, and 30%, respectively; jointing stage by 28, 32, and 36%, respectively; and flowering stage by 10, 26, and 16%, respectively, compared to T. These treatments also significantly reduced the soil–leaf water potential gradient at the 0–10 cm soil depth at the seedling stage by 35, 48, and 35%, respectively, and at the 30–50 cm soil depth at flowering by 62, 46, and 65%, respectively, compared to T. Thus, NTS, TP, and NTP reduced soil–leaf water transfer resistance and enhanced transpiration. Compared to T, the NTS, TP, and NTP practices increased biomass yield by 18, 36, and 40%; grain yield by 28, 22, and 24%; and WUEg by 24, 26, and 24%, respectively. These results demonstrate that no-till with straw mulch and plastic mulching with either no-till or conventional tillage decrease the soil–leaf water potential gradient and soil–leaf water transfer resistance and enhance sustainable intensification of wheat production in semi-arid areas

Panorama sobre las variaciones estacionales y diarias de la temperatura del suelo bajo el efecto de las costras biológicas en el centro-oeste de Argentina

Background and Aims: Biocrusts play an essential role on the earth’s surface and have a direct influence on soil parameters. Their effects on soil temperature are considered one of the most important because they affect ecological and hydrological processes, as well as the diversity of natural ecosystems. Although there are several studies concerning biocrust effects on the soil surface, investigations about the effect of the biocrust on soil temperature are still scarce. Our objective was to evaluate the influence of biocrusts on soil temperature conditions in drylands of central-western Argentina. Methods: Temperature values were recorded in the Monte phytogeographic region in the central-western part of Argentina, in three sites, during the dry and wet seasons in 2017-2018. We collected samples from a total of 30 randomly selected plots. We recorded daily temperatures values in two paired plots with crusted and uncrusted zones using a calibrated data logger Ibutton. The sampling took 18 days in total, three days on each site.Key results: Our results indicate that biocrusts produce a change in micro-soil temperatures. Areas in which biocrusts are present show a temperature reduction both in the wet and dry seasons. This effect is observed in the three studied sites. Temperature reduction varies according to the time of the day, study site and season. The morning, noon, and afternoon recorded the highest mean temperatures.Conclusions: The presence of biocrusts reduces soil temperatures in drylands of central-western Argentina. Large differences in mean temperature values between crusted and uncrusted zones were observed. The thermal reduction was more notorious in the hyper-arid site. How they affect their surrounding environment can be related to multiple factors, such as the composition of the microphytic community, the local climate and environmental conditions.Antecedentes y Objetivos: Las costras biológicas del suelo juegan un papel esencial en la superficie terrestre y tienen una influencia directa en los parámetros del suelo. Sus efectos sobre la temperatura del suelo se consideran uno de los más importantes debido a que afectan los procesos ecológicos e hidrológicos, así como la diversidad de los ecosistemas naturales. Aunque existen varios estudios sobre los efectos de la costra biológica en la superficie del suelo, las investigaciones sobre el efecto de la costra biológica en la temperatura del suelo aún son escasas. Nuestro objetivo fue evaluar la influencia de las costras biológicas en las condiciones de temperatura del suelo en zonas áridas del centro-oeste de Argentina.Métodos: Se registraron valores de temperatura en la región fitogeográfica del Monte en la parte centro-oeste de Argentina, en tres sitios, durante las estaciones seca y húmeda de 2017 y 2018. Colectamos muestras de un total de 30 parcelas seleccionadas al azar. Registramos valores de temperatura diarios en dos parcelas emparejadas con zonas con costras biológicas y sin costras biológicas utilizando un registrador de datos calibrado tipo Ibutton. El muestreo se llevó a cabo durante un total de 18 días, tres días en cada sitio. Resultados claves: Nuestros resultados indican que las costras biológicas producen un cambio en las temperaturas microambientales del suelo. Las áreas donde están presentes las costras biológicas muestran una reducción de la temperatura tanto en las estaciones húmedas como en las secas. Este efecto se observa en los tres sitios estudiados. La reducción de la temperatura varía de acuerdo con la hora del día, el sitio de estudio y la estación del año. La mañana, el mediodía y la tarde registraron las temperaturas medias más altas.Conclusiones: La presencia de costras biológicas reduce las temperaturas del suelo en las zonas áridas del centro-oeste de Argentina. Se observaron grandes diferencias en los valores medios de temperatura entre las zonas con costras biológicas y las zonas sin costras biológicas. La reducción térmica fue más notable en el sitio hiperárido. Cómo afectan su entorno circundante puede estar relacionado con múltiples factores, como la composición de la comunidad microfítica, el clima local y las condiciones ambientales

Isotopic dynamics of precipitation and its regional and local drivers in a plateau inland lake basin, Southwest China

Shrinkage of plateau lakes under climate strength has drawn growing attention. Because of its intricate implication to hydro-meteorological condition and climate system, stable isotopes in precipitation (e.g. delta H-2(p) and delta O-18(p)) provide us a powerful tool to understand the climate-hydrologic dynamics in shrinking lakes. However, how the regional atmospheric circulation, moisture sources and local fractionation processes drive isotopic variability from temporal to spatial scale has rarely been reported for remote plateau lakes. Hence, we collected a total of 98 rainfall samples at the south and the north shores of Chenghai lake, Yunnan-Guizhou Plateau to study the potential driving forces of precipitation isotope variability during the wet season of 2019. Based on backward trajectories of air masses obtained from HYSPLIT model, 68% of moisture came from delta O-18 depleted ocean (Indian Ocean, Bay of Bengal, South China Sea and Pacific Ocean), and the rainout process promoted the isotopic depletion when moisture arrived at the study basin. Evapotranspiration increased the heavy isotope ratios in precipitation originated from continents (northern China inland and western continents). The temporal dynamics of delta O-18(p) and delta H-2(p) were in phase with the convection activities intensity underlined the influence from large-scale atmospheric circulation. Local meteorological factors played a secondary role in isotope variability. Precipitation amount-effect strongly affected isotope ratios while mild anti-temperature effect was observed at daily scale. Interestingly, the rainfall isotope ratios showed different mechanisms in govern at lake south shore and north shore, with a distance of 19 km in between. This south-to-north difference can be explained by either lower 1.03% sub-evaporation in the south shore or 7% of recycled moisture contributing to precipitation in the north shore. Our findings discover the driving forces for delta O-18(p) variation and provide solid interpretations for hydro-climate change in Southwest China. (C) 2020 Elsevier B.V. All rights reserved.Peer reviewe

Investigating the role of evaporation in dew formation under different climates using 17O-excess

With increasing aridity in many regions, dew is likely to play an increasingly important role in the ecohydrological processes in many ecosystems, especially in arid and semiarid regions. Few studies investigated the role of evaporation during dew formation and how it varies under different climate settings. 17O-excess, as a new tracer, could be used to extract information of evaporation dynamics from natural water samples (e.g., precipitation, river, and lake). Therefore, to fill the knowledge gap in evaporation mechanisms during dew formation, we report the isotopic variation (δ2H, δ18O, δ17O, and 17O-excess) of dew and precipitation from three distinct climatic regions (i.e., Gobabeb in the central Namib Desert, Nice in France with Mediterranean climate, and Indianapolis in the central United States with humid continental climate). We examined whether dew formed in different climate settings was affected by different degree of evaporation using observed isotopic values and evaporation models during the formation processes, and modeled the effects of key meteorological variables (i.e., temperature and relative humidity) on 17O-excess variations. The results showed that dew in Gobabeb experienced kinetic fractionation associated with evaporation under non-steady state conditions during dew formation with enriched δ18O and low 17O-excess values. Dew formations with temperatures over 14.7 °C in Indianapolis were also influenced by evaporation under non-steady state conditions. However, dew formation in Nice did not experience significant evaporation. Evaporation processes (equilibrium or kinetic fractionation) occurring during nights with heavy dew under three climate settings were mainly related to the variation of atmosphere relative humidity. The 17O-excess tracer provides a new method to distinguish the different evaporation processes (equilibrium or kinetic fractionation) during dew formation and our result provides an improved understanding of dew formation

Carbon Capture and Storage

Climate change is one of the main threats to modern society. This phenomenon is associated with an increase in greenhouse gas (GHGs, mainly carbon dioxide—CO2) emissions due to anthropogenic activities. The main causes are the burning of fossil fuels and land use change (deforestation). Climate change impacts are associated with risks to basic needs (health, food security, and clean water), as well as risks to development (jobs, economic growth, and the cost of living). The processes involving CO2 capture and storage are gaining attention in the scientific community as an alternative for decreasing CO2 emissions, reducing its concentration in ambient air. The carbon capture and storage (CCS) methodologies comprise three steps: CO2 capture, CO2 transportation, and CO2 storage. Despite the high research activity within this topic, several technological, economic, and environmental issues as well as safety problems remain to be solved, such as the following needs: increase of CO2 capture efficiency, reduction of process costs, and verification of the environmental sustainability of CO2 storage

Light structures phototroph, bacterial and fungal communities at the soil surface

The upper few millimeters of soil harbour photosynthetic microbial communities that are structurally distinct from those of underlying bulk soil due to the presence of light. Previous studies in arid zones have demonstrated functional importance of these communities in reducing soil erosion, and enhancing carbon and nitrogen fixation. Despite being widely distributed, comparative understanding of the biodiversity of the soil surface and underlying soil is lacking, particularly in temperate zones. We investigated the establishment of soil surface communities on pasture soil in microcosms exposed to light or dark conditions, focusing on changes in phototroph, bacterial and fungal communities at the soil surface (0–3 mm) and bulk soil (3–12 mm) using ribosomal marker gene analyses. Microbial community structure changed with time and structurally similar phototrophic communities were found at the soil surface and in bulk soil in the light exposed microcosms suggesting that light can influence phototroph community structure even in the underlying bulk soil. 454 pyrosequencing showed a significant selection for diazotrophic cyanobacteria such as Nostoc punctiforme and Anabaena spp., in addition to the green alga Scenedesmus obliquus. The soil surface also harboured distinct heterotrophic bacterial and fungal communities in the presence of light, in particular, the selection for the phylum Firmicutes. However, these light driven changes in bacterial community structure did not extend to the underlying soil suggesting a discrete zone of influence, analogous to the rhizosphere