Arsenic-contaminated ground- and drinking water is a global environmental problem with about 1-2Prozent of the world's population being affected. The upper drinking water limit for arsenic (10 Micro g/l) recommended by the WHO is often exceeded, even in industrial nations in Europe and the USA. Chronic intake of arsenic causes severe health problems like skin diseases (e.g. blackfoot disease) and cancer. In addition to drinking water, seafood and rice are the main reservoirs for arsenic uptake. Arsenic is oftentimes of geogenic origin and in the environment it is mainly bound to iron(III) minerals. Iron(III)-reducing bacteria are able to dissolve these iron minerals and therefore release the arsenic to the environment. In turn, iron(II)-oxidizing bacteria have the potential to co-precipitate or sorb arsenic during iron(II)- oxidation at neutral pH followed by iron(III) mineral precipitation. This process may reduce arsenic concentrations in the environment drastically, lowering the potential risk for humans dramatically.The main goal of this study therefore is to quantify, identify and isolate anaerobic and aerobic Fe(II)-oxidizing microorganisms in arsenic-containing paddy soil. The co-precipitation and thus removal of arsenic by iron mineral producing bacteria will be determined in batch and microcosm experiments. Finally the influence of rhizosphere redox status on microbial Fe oxidation and arsenic uptake into rice plants will be evaluated in microcosm experiments. The long-term goal of this research is to better understand arsenic-co-precipitation and thus arsenic-immobilization by iron(II)-oxidizing bacteria in rice paddy soil. Potentially these results can lead to an improvement of living conditions in affected countries, e.g. in China or Bangladesh.
Water is an intrinsic component of ecosystems acting as a key agent of lateral transport for particulate and dissolved nutrients, forcing energy transfers, triggering erosion, and driving biodiversity patterns. Given the drastic impact of land use and climate change on any of these components and the vulnerability of Ecuadorian ecosystems with regard to this global change, indicators are required that not merely describe the structural condition of ecosystems, but rather capture the functional relations and processes. This project aims at investigating a set of such functional indicators from the fields of hydrology and biogeochemistry. In particular we will investigate (1) flow regime and timing, (2) nutrient cycling and flux rates, and (3) sediment fluxes as likely indicators. For assessing flow regime and timing we will concentrate on studying stable water isotopes to estimate mean transit time distributions that are likely to be impacted by changes in rainfall patterns and land use. Hysteresis loops of nitrate concentrations and calculated flux rates will be used as functional indicators for nutrient fluxes, most likely to be altered by changes in temperature as well as by land use and management. Finally, sediment fluxes will be measured to indicate surface runoff contribution to total discharge, mainly influenced by intensity of rainfall as well as land use. Monitoring of (1) will be based on intensive sampling campaigns of stable water isotopes in stream water and precipitation, while for (2) and (3) we plan to install automatic, high temporal-resolution field analytical instruments. Based on the data obtained by this intensive, bust cost effective monitoring, we will develop the functional indicators. This also provides a solid database for process-based model development. Models that are able to simulate these indicators are needed to enable projections into the future and to investigate the resilience of Ecuadorian landscape to global change. For the intended model set up we will couple the Catchment Modeling Framework, the biogeochemical LandscapeDNDC model and semi-empirical models for aquatic diversity. Global change scenarios will then be analyzed to capture the likely reaction of functional indicators. Finally, we will contribute to the written guidelines for developing a comprehensive monitoring program for biodiversity and ecosystem functions. Right from the beginning we will cooperate with four SENESCYT companion projects and three local non-university partners to ensure that the developed monitoring program will be appreciated by locals and stakeholders. Monitoring and modelling will focus on all three research areas in the Páramo (Cajas National Park), the dry forest (Reserva Laipuna) and the tropical montane cloud forest (Reserva Biologica San Francisco).
This project will provide quantitative estimates of the flow of low-salinity warm water through the Indonesian Gateway on suborbital timescales during MIS 2 and 3 (focusing on Dansgaard Oeschger (D-O) oscillations) and will assess the Indonesian Throughflow (ITF) s impact on the hydrography of the eastern Indian Ocean and global thermohaline circulation during this critical interval of high climate variability. ITF fluctuations, associated with sea level change, temperature and salinity variations in the West Pacific Warm Pool (WPWP) strongly influence precipitation over Australia, the strength of the southeast-Asian summer monsoon, and the intensity of warm meridional currents in the Indian Ocean. We will test the hypothesis that increased ITF is associated with warm interstadials of MIS 3, whereas a strong reduction in ITF occurred during stadials. We will use as main proxies planktonic and benthic foraminiferal isotopes in conjunction with Mg/Ca temperature estimates and radiogenic isotopes (mainly Nd) as tracers of Pacific water masses along depth transects in the Timor Passage and the eastern Indian Ocean. This project will provide the paleoceanographic framework that will be crucial to validate and refine circulation models of D-O events and high-frequency climate variability on a global scale.
Sulfur isotope fractionation (34S/32S) has been used since the late 1940s to study the chemical and biological sulfur cycle. While large isotope fractionations during bacterial sulfate reduction were used successfully to interpret, e.g., accumulation of sulfate in ancient oceans or the evolution of early life, much less is known about fractionation during sulfide oxidation. The fractionation between the two end-members sulfide and sulfate is commonly much smaller and inconsistencies exist whether substrate or product are enriched. These inconsistencies are explained by a lack of knowledge on oxidation pathways and rates as well as intermediate sulfur species, such as elemental sulfur, polysulfides, thiosulfate, sulfite, or metalloid-sulfide complexes (e.g. thioarsenates), potentially acting as 34S sinks.In the proposed project, we will develop a method for sulfur species-selective isotope analysis based on separation by preparative chromatography. Separation of Sn2- and S0 will be achieved after derivatization with methyl triflate on a C18 column, separation of the other sulfur species in an alkaline eluent on an AS16 column. Sulfur in the collected fractions will be extracted directly with activated copper chips (Sn2-, S0), or precipitated as ZnS (S2-) or BaSO4 and analyzed by routine methods as SO2. Results of this species-selective approach will be compared to those from previous techniques of end-member pool determinations and sequential precipitations.The method will be applied to sulfide oxidation profiles at neutral to alkaline hot springs at Yellowstone National Park, USA, where we detected intermediate sulfur species as important species. Determining 34S/32S only in sulfide and sulfate, our previous study has shown different fractionation patterns for two hot spring drainages with sulfide oxidation profiles that seemed similar from a geochemical perspective. The reasons for the different isotopic trends are unclear. In the present project, we will differentiate species-selective abiotic versus biotic fractionation using on-site incubation experiments with the chemolithotrophic sulfur-oxidizing bacteria Thermocrinis ruber as model organism. For selected samples, we will test whether 33S and 36S further elucidate species-selective sulfide oxidation patterns. We expect that lower source sulfide concentrations increase elemental sulfur disproportionation, thus increase redox cycling and isotope fractionation. We also expect that the larger the concentration of intermediate sulfur species, including thioarsenates, the larger the isotope fractionation. Following fractionation in species-selective pools, we will be able to clarify previously reported inconsistencies of 34S enrichment in substrate or product, elucidate sulfide oxidation pathways and rates, and reveal details about sulfur metabolism. Our new methodology and field-based data will be a basis for more consistent studies on sulfide oxidation in the future.
Degradation of the soil productivity due to salt accumulation (salinization) is a major concern in arid, semi-arid and coastal regions. Soil salinization is an old issue but encouraged irrigation practices have been rapidly increasing its intensity and magnitude in the past few decades. Studies have shown that excess of the irrigated water contributes significantly to evaporation from the bare soil surface and therefore to the salinization. In some parts of the world soil salinity has grown so acute that the agricultural lands have been abandoned. Evaporation salinization is mainly influenced by interaction between the flow and transport processes in the atmosphere and the porous-medium. On the atmosphere side, wind velocity, air temperature and radiation have a strong impact on evaporation. Furthermore, turbulence causes air mixing, influences the vapor transport and creates a boundary layer at the soil-atmosphere interface which indeed influences evaporation. On the porous-medium side, dissolved salt is transported under the influence of viscous forces, capillary forces, gravitational forces and advective and diffusive fluxes. The water either directly evaporates from the water-filled pores or it is transported to air due to diffusive processes. Continuous evaporation promotes salt accumulation and precipitation resulting in soil salinization. In the scope of this work we attempt to develop a model concept capable of handling flow, transport and precipitation processes related to evaporative salinization of an unsaturated porous-medium.
Proposed research: This research programme proposes to analyze the predictability of the hydrologic behaviour of Alpine ecosystems at the spatio-temporal scales relevant for water management, i.e. at spatial scales of between 200 km2 (e.g. a hydropower production catchment) and around 5000 km2 (e.g. flood management of the Swiss Rhone catchment) and at temporal scales ranging from hours to seasons. Research context: Quantitative stream flow predictions are essential for the sustainable management of our natural and man-made environment and for the prevention of natural hazards. Despite of ever better insights into the involved physical processes at the point scale, many existing catchment scale runoff prediction models still show a lack of reliability for stream flow prediction. The present research programme addresses this foremost issue in Alpine environments, which are the source of many major European rivers and play a dominant role for hydropower production and flood protection. Stream flow prediction in such environments is particularly challenging due to the high spatial variability of the meteorological driving forces opposed to notorious data scarcity in remote and high elevation areas. Project context: The present proposal is a follow-up proposal of the Ambizione project Hydrologic Prediction in Alpine Environments. During the main phase of the project (3 years), certain essential research objectives could not be reached, due namely to the maternity leave of the principal investigator (PI), but also due to additional research questions that emerged at the very beginning of this research. The present follow-up project proposes to complete the research programme during a complementary project phase (2 years). Objectives: The main objective of this research programme is to assess under which conditions simple hydrological models can give reliable stream flow predictions in Alpine environments. This objective will be reached based on an analysis of the variability of natural flow generation processes and of the variability of corresponding state-of-the-art hydrological model outputs. During the main phase of the project, the research was concentrated on the analysis of flow generation processes related to snowmelt, which in Alpine areas dominate the hydrological response over a large part of the year. The achieved results include a new hourly snowmelt model combined to a spatially-explicit precipitation-runoff model, an improved snowfall-limit prediction method for hydrological models and a weather generator that produces coupled temperature and prediction scenarios to analyze how these two meteorological variables integrate to the snow-hydrological response.(...)
The formation of calcite in otherwise carbonate-free acidic soils through the biological degradation of oxalate is a mechanism termed oxalate-carbonate pathway, which occurs during interaction between biological and geological systems. In this pathway, atmospheric CO2 is fixed by the photosynthetic activity of plants, part of which is destined to the production of oxalate to control the intracellular Ca2+ concentrations. An additional source of calcium oxalate is fungi, which are able to produce this organic acid to cope with elevated concentrations of metals. The decay of plant material results in a source of calcium oxalate for other trophic levels. In spite of its abundance as a substrate, oxalate is a very stable organic anion that can be metabolized only by a group of bacteria that use it as a carbon and energy source. These bacteria close the biological cycle by degrading calcium oxalate, releasing Ca2+ and changing the local soil pH. If the conditions are adequate, the geological part of the pathway begins because this biological process will indirectly lead to the precipitation of secondary calcium carbonate (calcite) under unexpected geological settings. The activity of the oxalate-carbonate pathway has now been demonstrated in several places around the world. Furthermore, it can constitute an important, although underestimated, soil mineral carbon sink. This is because due to the initial acidic soil conditions and the absence of geological carbonate in the basement, it is unexpected to find C in the form of calcite. By its global scale and its stability through a long period of time, this terrestrial C sink is of a crucial interest as the sustainability of other C sequestering processes (e.g. sinking of CO2 in the ocean) is under question. The study of the oxalate-carbonate pathway constitutes a multidisciplinary research that brings together competences in biology (botany, physiology, microbiology) and geology (geochemistry, mineralogy, soil science). Thus, from its inception, this research has been carried out by a multidisciplinary team and by combining two crucial aspects: field expeditions and laboratory work using several tropical soils as models. Our most recent results show that biological interactions between bacteria and fungi, that have been underestimated, are essential for reproducing the pathway in vitro. Also, we have observed that Ca budget/availability has a direct impact on pedogenic carbonate accumulations. By pursuing these two objectives, we expect to contribute essential information within two of the current 'black boxes' of the system, which will allow the establishment of a model of the dynamics of carbon accumulation associated with the oxalate-carbonate pathway. This may have an enormous impact due to the potential importance of this ecosystem (or equivalent ecosystems) in tackling the increasing atmospheric CO2 concentrations and their direct effect over global climate.
Temperatures in Switzerland increased about 0.57 C over the last three decades and climate models predict that this increase will continue during the 21st century and beyond. Accompanied by changes in the water supply due to the expected increase in the frequency and intensity of heavy precipitation and/or drought events, these effects will strongly force changes in forest productivity, spatial distribution of tree species, and changes in the species composition within forests. Projections of the future dimensions and interactions of these effects require detailed understanding of short and long-term changes in eco-physiological responses to past and present climate variation. Stable isotopes in tree rings have become a significant tool in obtaining retrospective insight into the plant physiological response to climate and other environmental variables. The increasing number of isotope records, however, also highlights important unsolved questions and current limitations of this tree-ring parameter. Obviously, an improved understanding of the mechanisms leading to variations in the tree's internal carbon and water cycle in relation to climate, soil moisture conditions, transpiration and expansion of the root system is urgently needed. ISOPATH aims to decipher the origin and variability of the isotopic signal in the tree rings of two alpine species, frequently used in climate reconstructions, and to understand the environmental and physiological information encoded. We will develop weekly resolved records of carbon and oxygen isotopes in xylem and needle water, needle sugars, phloem sugars and stem wood/cellulose of two physiologically differing species (larch and spruce) growing under varying temperature, soil moisture and relative humidity conditions. Those data will be related to a large suite of external variables including precipitation and soil water, temperature, and vapour pressure deficit. We act (i) on a spatial scale by following the complete pathway of stable isotopes from the atmosphere into the tree ring under varying environmental conditions and (ii) on a temporal scale by studying seasonal cycles of the isotope signals in all these different components, covering four growth seasons (2008-2011). This unique dataset in terms of length, resolution and number of measured variables will be used to test and improve advanced models for isotope fractionation at the leaf level and in the tree ring, in relation to species-specific traits, temperature and soil moisture conditions. The measured and modelled isotope signatures will allow to predict plant physiological adaptation in the alpine environment to climate change of the 21st century.
Global climate change will alter the species composition of forests with far reaching consequences for the biogeochemistry of the water, carbon and nitrogen cycles, the sustainability of economic development and even human health. The annual productivity of wood is substantial for the carbon sequestration and budget of the forests in Eurasia. Whereas a number of publications on the climatic influence on tree radial growth exist, little is known about the precise mechanisms of tree-ring formation, timing and rates of their growth, and about the influence of other exogenous factors such as forest fires, permafrost, or logging on biomass accumulation and carbon sequestration. An improved mechanistic understanding will be particularly important with respect to the prediction of future forest response. In the proposed project, we aim to study the influence of a changing climate on trees by analyzing the main factors controlling tree-ring growth in extreme conditions. We will focus our study on forest ecosystems in regions which are very sensitive to climatic changes and where rapid and dramatic environmental and climatic changes can take place: 1) The high latitude permafrost region in Central Siberia (Russia) 2) The semi-arid dry areas in Central Asia (Uzbekistan) 3) The high altitude temperature-sensitive region of the Swiss Alps (Lötschental, Switzerland). The conifer trees growing in these regions could be seriously damaged due to expected future changes in temperature, CO2 and water availability. The thawing of permafrost and increasing drought situation could be key factors influencing forest growth and possible forest decline. Tree ring samples from the above mentioned regions will be considered to analyze the climatic response according to the following approaches: Intra-seasonal dynamics of tree-ring formation will be recorded and correlated with monitored environmental factors, like air and soil temperature and humidity, permafrost depth and the isotope composition of soil water, precipitation, river and stream water. A broad network of dendrochronological data from different research stations will be developed for each region to cover various local conditions. Special attention will be paid to the carbon/water relations of trees by determination of stable isotope ratios of different ecosystem compartments and tree rings. Project partners are Paul Scherrer Institut, Switzerland (PSI), Swiss Federal Research Institute WSL, Switzerland (WSL), V.N.Sukachev Institute of Forest, Krasnoyarsk, Russia (IF) and Samarkand State University, Uzbekistan (UZ).
In rivers and streams, biofilms are major sites of carbon cycling. They retain large amounts of dissolved organic carbon (DOC) and consequently are most important for the development of aquatic organisms on higher trophic levels. Besides autochthonous primary production, which supports heterotrophic production in biofilms, large amounts of organic carbon (OC) are derived from the surrounding catchment areas. More precipitation and more frequent and severe floods due to climate change will increase the transport of material into streams. Moreover, catchment characteristics including vegetation affect the transport and nature of DOC into aquatic ecosystems. Thus, carbon dynamics depend on how a stream is embedded within and interacts with its surrounding terrestrial environment. Despite its importance for carbon cycling it is not understood to which extent autochthonous or allochthonous carbon is used in biofilms and how increased addition of allochthonous carbon determines the relative use of both carbon sources. The combined application of 13C and 14C analysis on differently labeled DOC sources intend to answer to which extent DOC from different sources is used by bacteria in biofilms and finally transported to higher trophic levels. The use of 13C and 14C signals on carbon compounds and biomarkers is an excellent method to determine carbon sources for microorganisms and the transport of labeled material within the food web.
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