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This article reviews the most recent results concerning second harmonic generation (SHG) experiments of non-phase matchable and phase matchable powder samples at high pressures and explains the pressure dependence of the intensity of the SHG signal by correlating it to the ratio between the average coherence length and the average particle size. The examples discussed here include pressure-induced structural changes in quartz, ZnO, ice VII and KIO3. It is shown that the second harmonic generation technique is a unique tool for the detection of pressure-induced structural phase transitions. It is laboratory based and allows fast measurements. It is complementary to X-ray diffraction and provides additional information about the presence of an inversion center for unknown or controversially discussed structures at high pressure.
Recently a considerable amount of effort has been put into quantifying how interactions of the carbon and nitrogen cycle affect future terrestrial carbon sinks. Dynamic vegetation models, representing the nitrogen cycle with varying degree of complexity, have shown diverging constraints of nitrogen dynamics on future carbon sequestration. In this study, we use LPJ-GUESS, a dynamic vegetation model employing a detailed individual- and patch-based representation of vegetation dynamics, to evaluate how population dynamics and resource competition between plant functional types, combined with nitrogen dynamics, have influenced the terrestrial carbon storage in the past and to investigate how terrestrial carbon and nitrogen dynamics might change in the future (1850 to 2100; one representative "business-as-usual" climate scenario). Single-factor model experiments of CO2 fertilisation and climate change show generally similar directions of the responses of C–N interactions, compared to the C-only version of the model as documented in previous studies using other global models. Under an RCP 8.5 scenario, nitrogen limitation suppresses potential CO2 fertilisation, reducing the cumulative net ecosystem carbon uptake between 1850 and 2100 by 61%, and soil warming-induced increase in nitrogen mineralisation reduces terrestrial carbon loss by 31%. When environmental changes are considered conjointly, carbon sequestration is limited by nitrogen dynamics up to the present. However, during the 21st century, nitrogen dynamics induce a net increase in carbon sequestration, resulting in an overall larger carbon uptake of 17% over the full period. This contrasts with previous results with other global models that have shown an 8 to 37% decrease in carbon uptake relative to modern baseline conditions. Implications for the plausibility of earlier projections of future terrestrial C dynamics based on C-only models are discussed.
Background: Dengue fever (DF) is the most rapidly spreading mosquito-borne viral disease in the world. In this decade it has expanded to new countries and from urban to rural areas. Nepal was regarded DF free until 2004. Since then dengue virus (DENV) has rapidly expanded its range even in mountain regions of Nepal, and major outbreaks occurred in 2006 and 2010. However, no data on the local knowledge, attitude and practice (KAP) of DF in Nepal exist although such information is required for prevention and control measures.
Methods: We conducted a community based cross-sectional survey in five districts of central Nepal between September 2011 and February 2012. We collected information on the socio-demographic characteristics of the participants and their knowledge, attitude and practice regarding DF using a structured questionnaire. We then statistically compared highland and lowland communities to identify possible causes of observed differences.
Principal findings: Out of 589 individuals interviewed, 77% had heard of DF. Only 12% of the sample had good knowledge of DF. Those living in the lowlands were five times more likely to possess good knowledge than highlanders (P<0.001). Despite low knowledge levels, 83% of the people had good attitude and 37% reported good practice. We found a significantly positive correlation among knowledge, attitude and practice (P<0.001). Among the socio-demographic variables, the education level of the participants was an independent predictor of practice level (P<0.05), and education level and interaction between the sex and age group of the participants were independent predictors of attitude level (P<0.05).
Conclusion: Despite the rapid expansion of DENV in Nepal, the knowledge of people about DF was very low. Therefore, massive awareness programmes are urgently required to protect the health of people from DF and to limit its further spread in this country.
The LPJ-GUESS dynamic vegetation model uniquely combines an individual- and patch-based representation of vegetation dynamics with ecosystem biogeochemical cycling from regional to global scales. We present an updated version that includes plant and soil N dynamics, analysing the implications of accounting for C–N interactions on predictions and performance of the model. Stand structural dynamics and allometric scaling of tree growth suggested by global databases of forest stand structure and development were well reproduced by the model in comparison to an earlier multi-model study. Accounting for N cycle dynamics improved the goodness of fit for broadleaved forests. N limitation associated with low N-mineralisation rates reduces productivity of cold-climate and dry-climate ecosystems relative to mesic temperate and tropical ecosystems. In a model experiment emulating free-air CO2 enrichment (FACE) treatment for forests globally, N limitation associated with low N-mineralisation rates of colder soils reduces CO2 enhancement of net primary production (NPP) for boreal forests, while some temperate and tropical forests exhibit increased NPP enhancement. Under a business-as-usual future climate and emissions scenario, ecosystem C storage globally was projected to increase by ca. 10%; additional N requirements to match this increasing ecosystem C were within the high N supply limit estimated on stoichiometric grounds in an earlier study. Our results highlight the importance of accounting for C–N interactions in studies of global terrestrial N cycling, and as a basis for understanding mechanisms on local scales and in different regional contexts.
Recently a considerable amount of effort has been put into quantifying how interactions of the carbon and nitrogen cycle affect future terrestrial carbon sinks. Dynamic vegetation models, representing the nitrogen cycle with varying degree of complexity, have shown diverging constraints of nitrogen dynamics on future carbon sequestration. In this study, we use the dynamic vegetation model LPJ-GUESS to evaluate how population dynamics and resource competition between plant functional types, combined with nitrogen dynamics, have influenced the terrestrial carbon storage in the past and to investigate how terrestrial carbon and nitrogen dynamics might change in the future (1850 to 2100; one exemplary "business-as-usual" climate scenario). Single factor model experiments of CO2 fertilisation and climate change show generally similar directions of the responses of C–N interactions, compared to the C-only version of the model, as documented in previous studies. Under a RCP 8.5 scenario, nitrogen limitation suppresses potential CO2 fertilisation, reducing the cumulative net ecosystem carbon uptake between 1850 and 2100 by 61%, and soil warming-induced increase in nitrogen mineralisation reduces terrestrial carbon loss by 31%. When environmental changes are considered conjointly, carbon sequestration is limited by nitrogen dynamics until present. However, during the 21st century nitrogen dynamics induce a net increase in carbon sequestration, resulting in an overall larger carbon uptake of 17% over the full period. This contradicts earlier model results that showed an 8 to 37% decrease in carbon uptake, questioning the often stated assumption that projections of future terrestrial C dynamics from C-only models are too optimistic.
Soil water potential is crucial to plant transpiration and thus to carbon cycling and biosphere–atmosphere interactions, yet it is difficult to measure in the field. Volumetric and gravimetric water contents are easy and cheap to measure in the field, but can be a poor proxy of plant-available water. Soil water content can be transformed to water potential using soil moisture retention curves. We provide empirically derived soil moisture retention curves for seven soil types in the Kruger National Park, South Africa. Site-specific curves produced excellent estimates of soil water potential from soil water content values. Curves from soils derived from the same geological substrate were similar, potentially allowing for the use of one curve for basalt soils and another for granite soils. It is anticipated that this dataset will help hydrologists and ecophysiologists understand water dynamics, carbon cycling and biosphere–atmosphere interactions under current and changing climatic conditions in the region.
During this study clumped isotope analysis of carbonates was established at the Goethe University of Frankfurt, Germany. Therefore, preparation protocols and analytical parameters were elaborated to obtain precise and accurate Δ47 data. Briefly, analyte CO2 was cleaned cryogenically using glass extraction lines to remove traces of water that enable re-equilibration of C–O bonds in the gases. Furthermore, analyte CO2 was passed through a gas chromatograph (GC) to clean it from contaminants that produce isobaric interferences with m/z 47. Initially, phosphoric acid digestions of carbonates was conducted at 25 °C in McCrea-type reaction vessels. Afterwards samples were reacted at 90 °C using a common acid bath. Mass spectrometric analyses were performed using a MAT 253 equipped with a dual inlet system. Δ47 values were directly projected to the absolute scale using CO2 gases equilibrated at distinct temperatures.
In cooperation with Stefano Bernasconi and his research group at ETH Zurich we studied the non-linearity that occurs for the measurement of m/z 47. This effect results from secondary electrons created by the m/z 44 beam. These electrons cause a negative background on the m/z 47 collector. A correction procedure was proposed that relies on the determination of the negative background on the m/z 47 Faraday cup. This approach might reduce time-consuming analyses of heated gases which were used so far to account for the observed non-linearity. However, the suggested correction of the negative background on the m/z 47 cup is only applicable if the slit width of the m/z 44 beam is significantly wider than that of the m/z 47 beam.
This thesis, furthermore, presents a comparison of the different phosphoric acid digestion techniques which are commonly used for carbonate clumped isotope analysis. For calcitic and aragonitic material digested at 25 °C in McCrea-type vessels we observed that the sample size has an effect on Δ47 data: higher mean Δ47 values and a larger scatter of data were received for samples <7 mg than for larger aliquots. For carbonate samples digested at 90 °C in a common acid bath no sample size effect was determined. We assume that secondary re-equilibration of CO2 with water preferentially occurs at 25 °C producing the observed differences. However, a sample size effect can be avoided if reaction temperature is increased to 90 °C.
In order to make carbonate Δ47 data obtained from acid digestions at 90 °C comparable to Δ47 data received from reactions at 25 °C the difference of the acid fractionation factores (Δ47*25-90) between both temperatures has to be known. For the determination of the Δ47*25-90 value we have considered Δ47 data made at 25 °C from samples >7 mg only. For calicte and aragonite we obtained differences in fractionation factores of 0.075‰ and 0.066‰, respectively. These Δ47*25-90 values are coincident with the theoretical prediction of 0.069‰ proposed for calcite (Guo et al., 2009).
Moreover, this dissertation comprises a calibration study of the clumped isotope thermometer based on various natural calcites that grew between 9 and 38 °C. The samples include a brachiopod shell, a bivalve shell, an eggshell of an ostrich and foraminifera tests which formed from distinct biomineralizing processes. Furthermore we included an authigenic carbonate crystallized from biological-induced precipitation. The following linear relationship between 1/T2 and Δ47 was determined (with Δ47 in ‰ and T in K):
Δ47 = 0.0327 (± 0.0026) x 106 / T2 + 0.3030 (± 0.0308) (R2 = 0.9915)
This equation differs from the pioneering Ghosh et al. (2006a) calibration. However, our regression line is statistically indistinguishable from that of Henkes et al. (2013) which is based on aragonitic mollusks and calcitic brachiopod shells. Both studies have in common that calibration data were, at first, directly referenced to the absolute scale. In addition, both datasets rely on similar digestion techniques. Furthermore, the two calibrations are conform with the theoretical prediction of Guo et al. (2009).
The calcite calibration of the clumped isotope paleothermometer received in this study was applied to Δ47 data measured for Silurian brachiopods shells from Gotland/Sweden. Prior to isotopic analysis the fossils were intensively investigated for their preservation state (CL, SEM, trace elements). The lowest T(Δ47) values of ca. 28 to 33 °C were estimated from ultrastructurally well-preserved regions of some shells. For these samples also the lowest δ18Ow values of Silurian seawater were determined. These estimates of ca. −1‰ confirm the assumption that the δ18O value of the Silurian ocean was buffered to (0 ± 1)‰.
Nevertheless, most studied shells were characterized by a patchwork of pristine and altered shell portions resulting in elevated T(Δ47) values which plot mostly between 40 and 60 °C. Our results indicate that the clumped isotopic composition of the shells were altered at low water-rock ratios, not affecting the δ18O values. Δ47 and δ18O data of associated diagenetic phases (sparitic and micritic phases of the inner fillings of the fossils) provide evidence that the sparitic cements grew during several diagenetic events which occurred at different temperatures in fluid-buffered systems. We, furthermore, conclude that the micritic phases lithified at a very early diagenetic stage with the δ18O values being most probably close to a Silurian seawater composition
Global-scale assessments of freshwater fluxes and storages by hydrological models under historic climate conditions are subject to a variety of uncertainties. Using the global hydrological model WaterGAP 2.2, we investigated the sensitivity of simulated freshwater fluxes and water storage variations to five major sources of uncertainty: climate forcing, land cover input, model structure, consideration of human water use and calibration (or no calibration). In a modelling experiment, five variants of the standard version of WaterGAP 2.2 were generated that differed from the standard version only regarding the investigated source of uncertainty. Sensitivity was analyzed by comparing water fluxes and water storage variations computed by the variants to those of the standard version, considering both global averages and grid cell values for the time period 1971–2000. The basin-specific calibration approach for WaterGAP, which forces simulated mean annual river discharge to be equal to observed values at 1319 gauging stations (representing 54% of global land area except Antarctica and Greenland), has the highest effect on modelled water fluxes and leads to the best fit of modelled to observed monthly and seasonal river discharge. Alternative state-of-the-art climate forcings rank second regarding the impact on grid cell specific fluxes and water storage variations, and their impact is ubiquitous and stronger than that of alternative land cover inputs. The diverse model refinements during the last decade lead to an improved fit to observed discharge, and affect globally averaged fluxes and storage values (the latter mainly due to modelling of groundwater depletion) but only affect a relatively small number of grid cells. Considering human water use is important for the global water storage trend (in particular in the groundwater compartment) but impacts on water fluxes are rather local and only important where water use is high. The best fit to observed time series of monthly river discharge (Nash–Sutcliffe criterion) or discharge seasonality is obtained with the standard WaterGAP 2.2 model version which is calibrated and driven by a sequence of two time series of daily observation-based climate forcings, WFD/WFDEI. Discharge computed by a calibrated model version using monthly CRU 3.2 and GPCC v6 climate input reduced the fit to observed discharge for most stations. Taking into account the investigated uncertainties of climate and land cover data, we estimate that the global 1971–2000 discharge into oceans and inland sinks is between 40 000 and 42 000 km3 yr−1. The range is mainly due differences in precipitation data that affect discharge in uncalibrated river basins. Actual evapotranspiration, with approximately 70 000 km3 yr−1, is rather unaffected by climate and land cover in global sum but differs spatially. Human water use is calculated to reduce river discharge by approximately 1000 km3 yr−1. Thus, global renewable water resources are estimated to range between 41 000 and 43 000 km3 yr−1. The climate data sets WFD (available until 2001) and WFDEI (starting in 1979) were found to be inconsistent with respect to short wave radiation data, resulting in strongly different potential evapotranspiration. Global assessments of freshwater fluxes and storages would therefore benefit from the development of a global data set of consistent daily climate forcing from 1900 to current.
In the past sixty years, excessive water consumption and dam construction have significantly influenced natural flow regimes and surface freshwater ecosystems throughout China, and thus resulted in serious environmental problems. In order to balance the competing water demands between human and environment and provide knowledge on sustainable water management, assessments on anthropogenic flow alterations and their impacts on aquatic and riparian ecosystems in China are needed.
In this study, the first evaluation on quantitative relationships between anthropogenic flow alterations and ecological responses in eleven river basins and watersheds in China was performed based on the data that could be obtained from published case studies. Quantitative relationships between changes in average annual discharge, seasonal low flow and seasonal high flow and changes in ecological indicators (fish diversity, fish catch and vegetation cover, etc.) were analyzed. The results showed that changes in riparian vegetation cover as well as changes in fish diversity and fish catch were strongly correlated with the changes in flow magnitude (r = 0.77, 0.66), especially with changes in average annual river discharge. In addition, more than half of the variations in vegetation cover could be explained by changes in average annual river discharge (r² = 0.63) and roughly 50 % changes in fish catch in arid and semi-arid region and 60% changes of fish catch in humid region could be related to alterations in average annual river discharge (r² = 0.53, 0.58).
In a supplementary analysis of this study, the first estimation on quantitative relationships between decreases in native fish species richness and anthropogenic flow alterations in 34 river basins and sub-basins in China was conducted. Linear relationships between losses of native fish species and five ecologically relevant flow indicators were analyzed by single and multiple regression models. For the single regression analysis, significant linear relationships were detected for the indicators of long-term average annual discharge (ILTA) and statistical low flow Q90 (IQ90). For the multiple regressions, no indicator other than ILTA has significant relationships with changes in number of fish species mainly due to collinearity. Two conclusions emerged from the analysis: 1) losses of fish species were positively correlated with changes in ILTA in China and 2) indicator of ILTA was dominant over other flow indicators included in this research for the given dataset. These results provide a guideline for the sustainable water resources management in rivers with high risk of fish extinction in China.
Irrigation intensifies land use by increasing crop yield but also impacts water resources. It affects water and energy balances and consequently the microclimate in irrigated regions. Therefore, knowledge of the extent of irrigated land is important for hydrological and crop modelling, global change research, and assessments of resource use and management. Information on the historical evolution of irrigated lands is limited. The new global Historical Irrigation Dataset (HID) provides estimates of the temporal development of the area equipped for irrigation (AEI) between 1900 and 2005 at 5 arc-minute resolution. We collected subnational irrigation statistics from various sources and found that the global extent of AEI increased from 63 million ha (Mha) in 1900 to 112 Mha in 1950 and 306 Mha in 2005. We developed eight gridded versions of time series of AEI by combining subnational irrigation statistics with different data sets on the historical extent of cropland and pasture. Different rules were applied to maximize consistency of the gridded products to subnational irrigation statistics or to historical cropland and pasture data sets. The HID reflects very well the spatial patterns of irrigated land in the western United States as shown on historical maps. Mean aridity on irrigated land increased and river discharge decreased from 1900–1950 whereas aridity decreased from 1950–2005. The dataset and its documentation are made available in an open data repository at https://mygeohub.org/publications/8 (doi:10.13019/M2MW2G).
Water footprints have been proposed as sustainability indicators, relating the consumption of goods like food to the amount of water necessary for their production and the impacts of that water use in the source regions. We further developed the existing water footprint methodology, by globally resolving virtual water flows from production to consumption regions for major food crops at 5 arcmin spatial resolution. We distinguished domestic and international flows, and assessed local impacts of export production. Applying this method to three exemplary cities, Berlin, Delhi and Lagos, we find major differences in amounts, composition, and origin of green and blue virtual water imports, due to differences in diets, trade integration and crop water productivities in the source regions. While almost all of Delhi's and Lagos' virtual water imports are of domestic origin, Berlin on average imports from more than 4000 km distance, in particular soy (livestock feed), coffee and cocoa. While 42% of Delhi's virtual water imports are blue water based, the fractions for Berlin and Lagos are 2 and 0.5%, respectively, roughly equal to the water volumes abstracted in these two cities for domestic water use. Some of the external source regions of Berlin's virtual water imports appear to be critically water scarce and/or food insecure. However, for deriving recommendations on sustainable consumption and trade, further analysis of context-specific costs and benefits associated with export production will be required.
The Sahel has been the focus of scientific interest in environmental-human dynamics and interactions. The objective of the present study is to contribute to the recent debate on the re-greening of Sahel. The paper examines the dynamics of barren land in the Sahel of Burkina Faso through analysis of remotely-sensed and rainfall data from 1975–2011. Discussions with farmers and land management staff have helped to understand the anthropogenic efforts toward soil restoration to enable the subsistence farming agriculture. Results showed that area of barren land has been fluctuating during the study period with approximately 10-year cyclicity. Similarly, rainfall, both at national and local levels has followed the same trends. The trends of the area of barren land and rainfall variability suggest that when rainfall increases, the area of barren land decreases and barren land increases when rainfall decreases. This implies that rainfall is one of the main factors driving the change in area of barren land. In addition, humans have contributed positively and negatively to the change by restoring barren lands for agriculture using locally known techniques and by accelerating land degradation through intensive and inappropriate land use practices.
Strong seasonal variability of hygric and thermal soil conditions are a defining environmental feature in Northern Australia. However, how such changes affect the soil–atmosphere exchange of nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2) is still 5 not well explored. By incubating intact soil cores from four sites (3 savanna, 1 pasture) under controlled soil temperatures (ST) and soil moisture (SM) we investigated the release of the trace gas fluxes of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to denitrification was measured using the helium gas flow soil core technique. Under dry pre-incubation conditions NO and N2O emission were very low (< 7.0± 5.0 μgNO-Nm−2 h−1; < 0.0± 1.4 μgN2O-Nm−2 h−1) or in case of N2O, even a net soil uptake was observed. Substantial NO (max: 306.5 μgNm−2 h−1) and relatively small N2O pulse emissions (max: 5.8±5.0 μgNm−2 h−1) were recorded following soil wetting, but these pulses were short-lived, lasting only up to 3 days. The total atmospheric loss of nitrogen was dominated by N2 emissions (82.4–99.3% of total N lost), although NO emissions contributed almost 43.2% at 50% SM and 30 °C ST. N2O emissions were systematically higher for 3 of 12 sample locations, which indicates substantial spatial variability at site level, but on average soils acted as weak N2O sources or even sinks. Emissions were controlled by SM and ST for N2O and CO2, ST and pH for NO, and SM and pH for N2.
Strong seasonal variability of hygric and thermal soil conditions are a defining environmental feature in northern Australia. However, how such changes affect the soil–atmosphere exchange of nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2) is still not well explored. By incubating intact soil cores from four sites (three savanna, one pasture) under controlled soil temperatures (ST) and soil moisture (SM) we investigated the release of the trace gas fluxes of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to denitrification was measured using the helium gas flow soil core technique. Under dry pre-incubation conditions NO and N2O emissions were very low (<7.0 ± 5.0 μg NO-N m−2 h−1; <0.0 ± 1.4 μg N2O-N m−2 h−1) or in the case of N2O, even a net soil uptake was observed. Substantial NO (max: 306.5 μg N m−2 h−1) and relatively small N2O pulse emissions (max: 5.8 ± 5.0 μg N m−2 h−1) were recorded following soil wetting, but these pulses were short lived, lasting only up to 3 days. The total atmospheric loss of nitrogen was generally dominated by N2 emissions (82.4–99.3% of total N lost), although NO emissions contributed almost 43.2% to the total atmospheric nitrogen loss at 50% SM and 30 °C ST incubation settings (the contribution of N2 at these soil conditions was only 53.2%). N2O emissions were systematically higher for 3 of 12 sample locations, which indicates substantial spatial variability at site level, but on average soils acted as weak N2O sources or even sinks. By using a conservative upscale approach we estimate total annual emissions from savanna soils to average 0.12 kg N ha−1 yr−1 (N2O), 0.68 kg N ha−1 yr−1 (NO) and 6.65 kg N ha−1 yr−1 (N2). The analysis of long-term SM and ST records makes it clear that extreme soil saturation that can lead to high N2O and N2 emissions only occurs a few days per year and thus has little impact on the annual total. The potential contribution of nitrogen released due to pulse events compared to the total annual emissions was found to be of importance for NO emissions (contribution to total: 5–22%), but not for N2O emissions. Our results indicate that the total gaseous release of nitrogen from these soils is low and clearly dominated by loss in the form of inert nitrogen. Effects of seasonally varying soil temperature and moisture were detected, but were found to be low due to the small amounts of available nitrogen in the soils (total nitrogen <0.1%).
So-called medicanes (Mediterranean hurricanes) are meso-scale, marine, and warm-core Mediterranean cyclones that exhibit some similarities to tropical cyclones. The strong cyclonic winds associated with medicanes threaten the highly populated coastal areas around the Mediterranean basin. To reduce the risk of casualties and overall negative impacts, it is important to improve the understanding of medicanes with the use of numerical models. In this study, we employ an atmospheric limited-area model (COSMO-CLM) coupled with a one-dimensional ocean model (1-D NEMO-MED12) to simulate medicanes. The aim of this study is to assess the robustness of the coupled model in simulating these extreme events. For this purpose, 11 historical medicane events are simulated using the atmosphere-only model, COSMO-CLM, and coupled model, with different setups (horizontal atmospheric grid-spacings of 0.44°, 0.22°, and 0.08°; with/without spectral nudging, and an ocean grid-spacing of 1/12°). The results show that at high-resolution, the coupled model is able to not only simulate most of medicane events but also improve the track length, core temperature, and wind speed of simulated medicanes compared to the atmosphere-only simulations. The results suggest that the coupled model is more proficient for systemic and detailed studies of historical medicane events, and that this model can be an effective tool for future projections.
In old and heavily weathered soils, the availability of P might be so small that the primary production of plants is limited. However, plants have evolved several mechanisms to actively take up P from the soil or mine it to overcome this limitation. These mechanisms involve the active uptake of P mediated by mycorrhiza, biotic de-occlusion through root clusters, and the biotic enhancement of weathering through root exudation. The objective of this paper is to investigate how and where these processes contribute to alleviate P limitation on primary productivity. To do so, we propose a process-based model accounting for the major processes of the carbon, water, and P cycles including chemical weathering at the global scale. Implementing P limitation on biomass synthesis allows the assessment of the efficiencies of biomass production across different ecosystems. We use simulation experiments to assess the relative importance of the different uptake mechanisms to alleviate P limitation on biomass production. We find that active P uptake is an essential mechanism for sustaining P availability on long timescales, whereas biotic de-occlusion might serve as a buffer on timescales shorter than 10 000 yr. Although active P uptake is essential for reducing P losses by leaching, humid lowland soils reach P limitation after around 100 000 yr of soil evolution. Given the generalized modelling framework, our model results compare reasonably with observed or independently estimated patterns and ranges of P concentrations in soils and vegetation. Furthermore, our simulations suggest that P limitation might be an important driver of biomass production efficiency (the fraction of the gross primary productivity used for biomass growth), and that vegetation on old soils has a smaller biomass production rate when P becomes limiting. With this study, we provide a theoretical basis for investigating the responses of terrestrial ecosystems to P availability linking geological and ecological timescales under different environmental settings.
The prediction of climate on time scales of years to decades is attracting the interest of both climate researchers and stakeholders. The German Ministry for Education and Research (BMBF) has launched a major research programme on decadal climate prediction called MiKlip (Mittelfristige Klimaprognosen, Decadal Climate Prediction) in order to investigate the prediction potential of global and regional climate models (RCMs). In this paper we describe a regional predictive hindcast ensemble, its validation, and the added value of regional downscaling. Global predictions are obtained from an ensemble of simulations by the MPI-ESM-LR model (baseline 0 runs), which were downscaled for Europe using the COSMO-CLM regional model. Decadal hindcasts were produced for the 5 decades starting in 1961 until 2001. Observations were taken from the E-OBS data set. To identify decadal variability and predictability, we removed the long-term mean, as well as the long-term linear trend from the data. We split the resulting anomaly time series into two parts, the first including lead times of 1–5 years, reflecting the skill which originates mainly from the initialisation, and the second including lead times from 6–10 years, which are more related to the representation of low frequency climate variability and the effects of external forcing. We investigated temperature averages and precipitation sums for the summer and winter half-year. Skill assessment was based on correlation coefficient and reliability. We found that regional downscaling preserves, but mostly does not improve the skill and the reliability of the global predictions for summer half-year temperature anomalies. In contrast, regionalisation improves global decadal predictions of half-year precipitation sums in most parts of Europe. The added value results from an increased predictive skill on grid-point basis together with an improvement of the ensemble spread, i.e. the reliability.
This study describes the Holocene sedimentary lagoonal deposition history, including event sedimentation and benthic foraminiferal analyzes, from about 10 kyrs BP until today. This is the first study describing the sedimentation of a Maldivian atoll lagoon in such detail. Thirty-nine sediment cores have been recovered from the deep Rasdhoo Atoll lagoon of the Maldives (4°N/73°W). Seventeen sediment cores were opened, described, and 296 sediment samples have been collected and analyzed. Different methods have been used to evaluate the coarse- and fine-grained carbonate components and a total of fifty-eight samples have been dated radiometrically by Beta Analytic Inc., Miami, Florida. In general, the Rasdhoo Atoll lagoon sediments can be divided into (1) a Late Pleistocene soil, (2) an early Holocene peat layer composed of mangrove deposits which mark the beginning inundation of the atoll lagoon by the rising Holocene sea-level at 10,320 ± 100 yrs BP, and (3) carbonate sediments starting to fill up the lagoon 7850 ± 140 yrs BP until today. The transition from peat to carbonate is characterized by a considerable hiatus. Six different carbonate sediment facies are classified by statistical analyses, listed in decreasing abundance:
(1) mollusk-coral-algal floatstone to rudstone (30%)
(2) mollusk-coral-red algae rudstone (23%)
(3) mollusk-coral-algal wackestone to floatstone (23%)
(4) mollusk-coral wackestone (13%)
(5) mollusk-coral mudstone to wackestone (9%)
(6) mollusk mudstone (2%)
Based on grain-sizes in combination with coral identification, the facies represent both lagoonal background sedimentation (mostly fine-grained sediments (matrix >50%)) and event sedimentation (coarse-grained sediment layers composing reefal components).
Six coarser grained layers in muddy background sediments of the Rasdhoo Atoll lagoon were interpreted as Holocene tsunami events, based on the increase of allochthonous skeletal material with shallow-water reef affinity such as fragments of shallow-water coral species, coralline red algae, and reef-dwelling foraminifera in these layers, as well as AMS dating:
• Event 1: 420 - 890 yrs BP (655 yrs BP)
• Event 2: 890 - 1560 yrs BP (1225 yrs BP)
• Event 3: 2040 - 2340 yrs BP (2190 yrs BP)
• Event 4: 2420 - 3380 yrs BP (2900 yrs BP)
• Event 5: 3890 - 4330 yrs BP (4110 yrs BP)
• Event 6: 5480 - 5760 yrs BP (5620 yrs BP)
Five of the six layers may be correlated to previously published tsunami events at adjacent coastal research sites. The mid-late Holocene atoll lagoon archive is incomplete though based on the assumption that major earthquakes at the Indonesian subduction zone generated more than six major tsunamis during the past 6.5 kyrs.
According to Gischler (2006), the sediments of the Rasdhoo Atoll lagoon can be divided into two areas: (1) a central to marginal deep lagoon with a lateral west-to-east gradient of sediment facies distribution, visible in sections <4 kyrs BP with sedimentary facies of mudstone to wackestone in the western part (e.g., cores 16, 18, and 34) and coarse-grained coral and algal-rich sediments in the eastern part of the lagoon (e.g., cores 30 and 31). (2) A northern enclosed and shallow area between the sand apron and the sand spit accumulating “sandy” sediments of wackestone facies (cores 2, 19, 25, and 26).
Comparing the sediment accumulation data of the lagoon with two reconstructed local sea-level curves, three different sequence-stratigraphical systems tracts are visible: (1) a lowstand systems tract (LST) >10 kyrs BP. Pleistocene brownish soil superposing subaerially exposed Pleistocene reef limestone. (2) A transgressive systems tract (TST) 10-6.5 kyrs BP. A peat layer marks the beginning of the inundation, and the carbonate sedimentation starts with very low sedimentation rates of 0.02 m/kyr. (3) A highstand systems tract (HST) 6.5-0 kyrs BP, further divided into three stages (6.5-3, 3-1, 1-0 kyrs BP). The sea-level rise slowed down, sedimentation rates are increasing continuously up to a maximum of 1.4 m/kyr, the sand spit developed some 4 kyrs BP, the lagoonal circulation got restricted, and the lateral west-to-east gradient of grain-size accumulation started. From 1-0 kyrs BP the sedimentation rates slowed down to modern mean sedimentation rates of 0.6 m/kyr.
Two cores, one core from the center of the lagoon (core 16) and one core from the northern margin of the lagoon (core 19), have been analyzed on diversity and assemblages of benthic foraminifera in high-resolution. The transitions of Ammonia spp. to a more even and diverse fauna marks a significant environmental change at 7.0 kyrs BP in core 16 (onset of a stable environment in the deep lagoon after the sea-level rise slowed down at HST stage 1) and at 4.0 kyrs BP in core 19. A continuing environmental change after 1.4 kyrs BP in core 16 caused the fauna to become more even, a recovery of diversity and a permanent decline of foraminiferal accumulation rate. The changes in the faunas at 4.0 kyrs BP and at 1.4 kyrs BP could be explained with the sand spit formation in the northwestern and western lagoon. The sand spit has apparently acted as an obstacle in lagoonal circulation and might have caused unstable environmental conditions due to a more rapid circulation at the shallow marine site of core 19 and a slowdown of bottom water circulation in the main lagoon (core 16) leading to higher residence times and to lower oxygen and higher nutrient concentrations.
The objective of the present doctoral thesis was to investigate the occurrence, distribution, and behaviour of six hydrophilic ethers: ethyl tert-butyl ether (ETBE), 1,4-dioxane, ethylene glycol dimethyl ether (monoglyme), diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), and tetraethylene glycol dimethyl ether (tetraglyme) in surface-, waste-, ground- and drinking water samples. Solid phase extraction and gas chromatography/mass spectrometry were used to analyze the six hydrophilic ethers. Altogether more than 150 surface water samples, almost 100 of each groundwater and wastewater samples, and 10 raw and drinking water samples were analyzed during the research project.
Initially, the method was validated in order to simultaneously determine the analytes of interest in various aquatic environments. A solid phase extraction method that uses coconut charcoal (Resprep® activated coconut charcoal, Restek) or carbon molecular sieve material (SupelcleanTM Envi-CarbTM Plus, Supelco) for analyte absorption were found suitable for determination of ETBE, 1,4-dioxane, and glymes in surface-, drinking-, ground- and wastewater samples. Precision and accuracy of both methods was demonstrated for all analytes of interest. The recovery of target compounds from the ultrapure water spiked at 1.0 µg L−1 was between 86.8 % and 98.2 %, with relative standard deviation below 6 %. The samples spiked at 10.0 µg L−1 gave slightly higher recovery of 90.6 % to 112.2 % with a relative standard deviation below 3.4 % for each analyte. Detection and quantification limits in ultrapure water and surface waters were furthermore established. The limit of quantitation (LOQ) in ultrapure water ranged between 0.024 µg L−1 to 0.057 µg L−1 using Restek cartridges, and 0.030 µg L−1 to 0.069 µg L−1 using Supelco cartridges. In the surface water samples the calculated LOQ was 0.032 µg L−1 to 0.067µg L−1 using coconut charcoal material and 0.032 µg L−1 to 0.052 µg L−1 using the carbon molecular sieve material. Moreover, stability of the unpreserved and preserved water samples as well as the extracts was determined. Preservation of samples with sodium bisulfate (at 1 gram per Liter) resulted in much better stability of the ethers in water samples. Subsequently, 27 samples obtained from seven surface water bodies in Germany (Rivers Rhine, Lippe, Main, Oder, Rur, Schwarzbach and Wesel-Datteln Canal) were analyzed for the six hydrophilic ethers. ETBE was present in only two surface waters (Rhine River and Wesel-Datteln Canal) with concentrations close to the LOQ (up to 0.065 µg L−1). 1,4-Dioxane was detected in all of the water samples at concentrations reaching 1.93 µg L–1. Monoglyme was identified only in the Main and Rhine Rivers at the maximum concentration of 0.114 µg L–1 and 0.427 µg L–1, respectively. Very high concentrations (up to 1.73 µg L−1) of diglyme, triglyme, and tetraglyme were detected in the samples from the Oder River. These glymes were also detected in the Rhine River; however the concentrations did not exceed 0.200 µg L–1. Furthermore, tetraglyme was detected in the Main River at an average concentration of 0.409 µg L–1 (n = 6) and in one sample from the Rur River at 0.192 µg L–1.
Four sampling campaigns were conducted at the Oderbruch polder between October 2009 and May 2012, in order to study the behavior of the hydrophilic ethers and organophosphates during riverbank filtration and in the anoxic aquifer. Moreover the suitability of these target compounds was assessed for their use as groundwater organic tracers. At the time of each sampling campaign, concentrations of triglyme and tetraglyme in the Oder River were between 20–185 ng L–1 (n = 4) and 273¬–1576 ng L–1 (n = 4). Monoglyme, diglyme, and 1,4-dioxane were analyzed only during the two last sampling campaigns. At that time, the concentration of diglyme in Oder River was 65¬–94 ng L-1 (n = 2) and 1,4-dioxane 1610¬–3290 ng L–1 (n = 2). In the drainage ditch, following bank filtration, concentrations of ethers ranged between 1090 ng L–1 and 1467 ng L–1 for 1,4-dioxane, 23¬ng L–1 and 41 ng L–1 for diglyme, 37 ng L–1 and 149 ng L–1 for triglyme, and 496 ng L–1 and 1403 ng L–1 for tetraglyme. In the anoxic aquifer, 1,4-dioxane showed the greatest persistence during the groundwater passage. At the distance of 1150 m from the river and an estimated groundwater age of 41.9 years, a concentration above 200 ng L−1 was detected. A positive correlation was found for the inorganic tracer chloride (Cl−) with 1,4-dioxane and tetraglyme. Similarities in the behavior of Cl− and the organic compound suggested that 1,4-dioxane and tetraglyme are controlled by the same hydraulic process and therefore can be used as additional tracers to study the dynamics of the groundwater system. These results show that high concentrations of ethers are present in the surface water and are not removed during bank filtration processes. Moreover, the hydrophilic ethers persist in the anoxic aquifer and little or no degradation is expected, supporting, their possible application as organic tracers.
A separate sampling project was conducted for 1,4-dioxane that focused primarily on its fate in the aquatic environment. This study provided missing information on the extent of water pollution with 1,4-dioxane is Germany. Numerous waste-, surface-, ground- and drinking water samples were collected in order to determine the persistence of 1,4-dioxane in the aquatic environment. The occurrence of 1,4-dioxane was determined in wastewater samples from four municipal sewage treatment plants (STP). The influent and effluent samples were collected during weekly campaigns. The average influent concentrations in all four plants ranged from 262 ± 32 ng L−1 to 834 ± 480 ng L−1, whereas the average effluents concentrations were between 267 ± 35 ng L−1 and 62,260 ± 36,000 ng L−1. The source of increased 1,4-dioxane concentrations in one of the effluents was identified to originate from impurities in the methanol used in the postanoxic denitrification process. Spatial and temporal distribution of 1,4-dioxane in the river Main, Rhine, and Oder was also examined. Concentrations reaching 2,200 ng L−1 in the Oder River, and 860 ng L−1 in both Main and Rhine River were detected. The average load during the sampling was estimated to be 6.5 kg d−1 in the Main, 34.1 kg d−1 in the Oder, and 134.5 kg d−1 in the Rhine River. In all of the sampled rivers, concentrations of 1,4-dioxane increased with distance from the mouth of the river and were found to negatively correlate with the discharge of the river. In order to determine if 1,4-dioxane can reach drinking water supplies, samples from a Rhine River bank filtration site and potable water from two drinking water production facilities were analyzed for the presence of 1,4-dioxane in the raw water and finished potable water. The raw water (following bank filtration) contained 650 ng L−1 to 670 ng L−1 of 1,4-dioxane, whereas the concentration in the finished drinking water fell only to 600 ng L−1 and 490 ng L−1, respectively.
During the final project, investigations of the source identification of high glyme concentrations in the Oder River were carried out. During four sampling campaigns between January, 2012 and April, 2013, 50 samples from the Oder River in the Oderbruch region and Poland were collected. During the first two samplings in the Oderbruch polder, glymes were detected at concentration reaching 0.07 µg L-1 (diglyme), 0.54 µg L−1 (triglyme) and 1.73 µg L−1 (tetraglyme) in the Oder River. The extensive sampling campaign of the Oder River (about 500 km) in Poland helped to identify the area of possible glyme entry into the river. During that sampling the maximum concentrations of triglyme and tetraglyme were 0.46 µg L−1 and 2.21 µg L−1, respectively. A closer investigation of the identified area of pollution, helped to determine the possible sources of glymes in the Oder River. Hence, the final sampling focused on the Kaczawa River, a left tributary of the Oder River and Czarna Woda, a left tributary of Kaczawa River. Moreover, samples from an industrial wastewater treatment plant were collected. Samples from Czarna Woda stream and Kaczawa River contained even higher concentrations of diglyme, triglyme, and tetraglyme, reaching 5.18 µg L−1, 12.87 µg L−1 and 80.81 µg L−1, respectively. Finally, three water samples from a wastewater treatment plant receiving influents from a copper smelter were analyzed. Diglyme, triglyme, and tetraglyme were present at an average concentration of 569 µg L−1, 4300 µg L−1, and 65900 µg L−1, respectively in the wastewater. Further research helped to identify the source of the glymes in the wastewater. The gas desulfurization process – Solinox implemented in the nearby copper smelter uses glymes as physical absorption medium for sulfur dioxide.
Results of this doctoral research provide important information about the occurrence, distribution, and behavior of hydrophilic ethers: 1,4-dioxane, monoglyme, diglyme, triglyme, and tetraglyme in the aquatic environment. A method capable of analyzing a wide range of ether compounds: from a volatile ETBE to a high molecular weight tetraglyme was validated. 1,4-Dioxane and tetraglyme were found to be applicable as organic tracers, since they are not easily attenuated during bank filtration and the anoxic groundwater passage. The extent of water pollution with 1,4-dioxane was shown in waste-, surface-, ground-, and drinking waters. One source of extremely high concentrations of 1,4-dioxane in a municipal sewage treatment plant applying postanoxic denitrification was identified, however more information is needed on the entry of 1,4-dioxane into surface waters. Moreover, 1,4-dioxane was present in drinking water samples from river bank filtration, which demonstrates its persistence in the aquatic environment and its low degradation potential during bank filtration and subsequent water treatment. Furthermore, this was the first study that focused primarily on identifying sources of glymes in surface waters. Glymes find a widespread use in industrial sectors, hence establishing their origin in the surface water is difficult (as with 1,4-dioxane). In this work, a gas desulphurization process was identified to be a dominating source of glyme pollution in the Oder River.
It is common practice to use a 30-year period to derive climatological values, as recommended by the World Meteorological Organization. However this convention relies on important assumptions, of which the validity can be examined by deriving the uncertainty inherent to using a limited time-period for deriving climatological values. In this study a new method, aiming at deriving this uncertainty, has been developed with an application to precipitation for a station in Europe (Westdorpe) and one in Africa (Gulu). The weather generator framework is used to produce synthetic daily precipitation time-series that can also be regarded as alternative climate realizations. The framework consists of an improved Markov model, which shows good performance in reproducing the 5-day precipitation variability. The sub-seasonal, seasonal and the inter-annual signals are introduced in the weather generator framework by including covariates. These covariates are derived from an empirical mode decomposition analysis with an improved stability and significance assessment. Introducing covariates was found to substantially improve the monthly precipitation variability for Gulu. From the weather generator, 1,000 synthetic time-series were produced. The divergence between these time-series demonstrates an uncertainty, inherent to using a 30-year period for mean precipitation, of 11 % for Westdorpe and 15 % for Gulu. The uncertainty for precipitation 10-year return levels was found to be 37 % for both sites.