1,721,009 research outputs found
Are algal blooms occurring later in Lake Taihu? Climate local effects outcompete mitigation prevention
No full textUsing Landsat and Moderate-resolution Imaging Spectroradiometer (MODIS) satellite data, cyanobacteria bloom initiation dates over two decades (1987-2011) in Lake Taihu showed three distinct trends. Initial blooms occurred later each year between 1987 and 1997 and then generally earlier until 2007, when the earliest and most extensive blooms occurred. After 2007, bloom initiation dates occurred later each year. Climate and catchment control over bloom dynamics was observed, in particular winter temperature minima and nutrient ratios. © 2014 The Author 2014
The use of system analysis methods in the sustainable managements of wetlands
No full textThe management of the utilisation of natural resources from wetland ecosystems is a multiobjective and complex task. The creation of innovative decision making tools for sustainable wetland resource utilisation is an important challenge for the future. This is particularly crucial in the light of the growing shortages for high quality freshwater and the vanishing habitat for a large number of wetland fauna and flora species. Because wetlands combine attributes of both aquatic and terrestrial ecosystems, wetlands are often at the crossroads of a number of disciplines with no specific discipline of its own. Therefore, management programmes require a multidisciplinary approach founded on a systematic monitoring of key biological and physical parameters. A European Commission DG XII research project dedicated to the development of management tools for wetland resources in Latin America is being developed by a multidisciplinary team of researchers from eight universities, located in four EU member states, Argentina and Brazil. The study sites that will be utilised for this analysis are two shallow lakes in Northeast Argentina within the large (13 000 km2) wetland `Esteros del Ibera'. Continuous and periodic in-situ monitoring instrumentation has been installed in a long term monitoring programme of hydrological and meteorological factors, coupled with monthly biological and ecological data gathering. Potential future scenarios for wetland resource use are being discussed in a series of public meetings with key provincial and local actors (teachers, university professors, clergymen, local business persons and politicians). These meetings address both the small scale modifications of wetland use (water extraction for agriculture, tourism, controlled hunting) as well as regional projects related to the creation of large scale economic development (forestation, modification of nearby waterways for hydroelectric production and increased river transportation). Models are developed relating the chemical, physical, biological and ecological parameters monitored. These models will be dedicated to analysing the effects of development on wetland functions and resource quality. An economic model will be created to evaluate potential modifications in wetland functions in the local and regional socio-economic context. Evaluation instruments are developed and tested which include; qualitative models using loop analysis, goal functions based on the aquatic trophic web and the overall energy flux in the lagoon, and a geographical information system utilising satellite images. The purpose of these instruments is to examine the overall impacts of development alternatives on resource quality and ecosystem integrity, as well as demonstrating key parameters that should be more closely monitored. The final package will include an evaluation of the potential impacts of the development scenarios proposed by the key actors, recommendations to reduce specific impacts through alternative technologies, together with a monitoring programme and analysis tools for improved decision making in wetland resource management
Selective Mechanochemical Dehalogenation of Chlorobenzenes over Calcium Hydride
No full textWe have shown that in the presence of a reactive substrate, chlorinated organic compounds can be dehalogenated by mechanical treatment, and a specific reaction product can be obtained. We have used a ball milling process at low temperature and atmospheric pressure to produce a dechlorination of up to 100% for both liquid and solid chlorinated compounds. The products of the completed reaction for trials with hexachlorobenzene and chlorobenzene were both principally restricted to benzene and chloride salts. The use of CaH2 as a source of active hydrogen produces a much more specific reaction in significantly less time in comparison with CaO and MgO substrates reacted under hydrogen atmosphere. The process was found to depend on the injected mechanical energy and the collision frequency. In the case of hexachlorobenzene, an explosive-type reaction was observed to occur at specific milling times as a function of the kinetic energy employed
The mechanochemical self-propagating reaction between hexachlorobenzene and calcium hydride
No full textWe report on studies of the solid state reaction between hexachlorobenzene and calcium hydride carried out by high-energy ball milling. The transformation behavior depends on the intensity of the mechanical energy transferred to the reactants at the impact. At lower energy regimes, chemical conversions increase gradually as a function of the milling time and a large excess of calcium hydride was found to favor the reaction rate. Calcium hydride–chloride and benzene are formed as end products. Beyond an impact energy threshold, self-sustaining transformations were observed leading to an instantaneous transformation to hydrogen, graphite, and depending upon the reactant molar ratio, to calcium hydride–chloride or calcium chloride. The sudden increase of the reactor-vial temperature was proportional to the hexachlorobenzene content in the reacting mixture and the total heat evolved was found to be in good agreement with the forecasted reaction enthalpies. The ignition time, i.e., the milling time at which the combustion-like event occurs, was followed as a function of the reactant composition. The incubation period rapidly decreases by increasing the calcium hydride to hexachlorobenzene molar ratio, that is, moving away from the stoichiometric composition at which calcium chloride forms predominantly. Some suggestions concerning the activation energy of the two competing end products were inferred from the mechanochemical yield which has been calculated as the ratio between the moles of reacted hexachlorobenzene divided by the total injected energy dose. Keeping the molar composition constant and modulating the shock power intensity, the self-sustaining reaction takes place only when the same dose of mechanical energy has been supplied to the reacting system, irrespective of the single impact energy
Testing the spectral variation hypothesis by using satellite multispectral images
No full textIn the present paper, a test of the spectral variation hypothesis (SVH) was performed using multispectral high resolution satellite data. The SVH was tested by comparing the relationship between the spectral heterogeneity and species richness in plots of different size (100-10000 m2) in a complex wetland ecosystem, the "Montepulciano Lake", Central Italy. The nature reserve of the Montepulciano Lake is centered on a 100 ha shallow lake surrounded on three sides by a Phragmites australis and Carex sp. pl. marsh of about 280 ha. The monitoring program for the reserve vegetation started in 2002 and is based on the analysis of 1, 100 m2 and 1 ha (10000 m2) plots, organized in such a manner that four of the smaller size plots are nested, following a random design, within a larger one. Data on species composition and community structure were collected in the plots and stored in a GIS-linked archive. A multispectral Quickbird satellite image (3 m spatial resolution) acquired of the wetland and lake ecosystem during the same period was radiometrically and geometrically corrected. We performed an analysis to examine the use of spectral heterogeneity using the four visible and infrared wavebands of the satellite image to predict species richness at the different spatial scales. The spectral heterogeneity was found to explain about 20% of the variance of species richness at the 100 m2 scale and about 50% at the 1 ha scale. It was concluded that multispectral high resolution satellite data can contribute to the biodiversity assessment of complex wetland ecosystem
Short-term dynamics of physico-chemical and biological features in a shallow, evaporative antarctic lake
No full textLakes are among the most productive and biodiverse ecosystems in Antarctica, and they behave as important indicators of local climatic and environmental changes. However, few studies have focused on the local drivers of short-term temporal variability in lacustrine biogeochemical variables. In the present study, measurements of physical, chemical, biological and optical characteristics of the shallow endorheic Lake 14 at Edmonson Point (74.33° S, 165.13° E) were made over the ice-free period in December 2006. A significant variation in most variables was observed. Possible drivers for these changes were the loss of the ice cover, an increase in solar irradiance, a change in photosynthetic activity and the evaporative loss of water. By removing relative changes due to evaporative losses, new insights were gained into the driving factors controlling the biogeochemistry and primary productivity in the shallow Antarctic lake. In particular, a decrease in phytoplankton biomass was observed and was probably linked to photoinhibition as revealed by an increase in photoprotective pigments. The absorbance by dissolved organic matter, when weighted with respect to evaporative loss, shows an overall reduction in humic-like absorption, most likely linked to photodegradation. © 2013 Springer-Verlag Berlin Heidelberg
Functioning and dynamics of wetland vegetation of Lake Victoria: an overview
No full texthe aquatic macrophytic vegetation constituting the wetlands situated along the coast of Lake Victoria provides valuable services to both local and regional communities as well as an important ecological function through the transition between terrestrial and aquatic ecosystems. The wetland vegetation is typically rooted in the substrate on the landward side of the lake, but forms a floating mat towards the middle of the wetland and at the wetland/lake interface. Cyperus papyrus and Miscanthidium violaceum vegetation typically dominate the permanently inundated wetland areas along most of the shores of Lake Victoria. Due to the prevailing climatic and hydrological catchment conditions, these macrophytic plants (papyrus in particular) tend to exhibit high net productivity and nutrient uptake which strongly influences both wetland status and lake water quality. In addition, these wetlands provide important economic livelihoods for the local populations. The integrity and physical structure of these wetlands strongly influences their associated mass transport mechanisms (water, nutrients and carbon) and ecosystem processes. Wetland degradation in Africa is an increasing problem, as these ecosystems are relied upon to attenuate industrial, urban and agricultural pollution and supply numerous services and resources. In an integrated project focused on the wetlands of Lake Victoria, the ecological and economic aspects of littoral wetlands were examined and new instruments developed for their sustainable management
Assimilation of MODIS Chlorophyll-a Data Into a Coupled Hydrodynamic-Biological Model of Taihu Lake
No full textMODIS chlorophyll-a concentration (Chla) data were assimilated into a coupled hydrodynamic-biological model using an Optimal Interpolation method. Simulations were conducted using MODIS data covering Taihu Lake in May 2009, when algal blooms typically begin to occur. The results of the assimilation approach showed improvements in the estimation of Chla distributions in spatial coherency and temporal continuity. Bias of assimilation (model run after assimilation) was 5.1%, with a RMSE of 49.7%. In comparison, the free run (model run without assimilation) had a bias of -34.9% and RMSE of 176.5%. In situ data used for comparison showed reduced RMSE and the Bias for assimilation. Two sensitivity experiments were used to determine the suitable correlation length scale with respect to observation data accuracy. The result showed that 500m is the optimum scale to construct the background error covariance matrix. The sensitivity experiment of observational data accuracy also showed that more accurate observation data allowed for better assimilation results
Unusual links between inherent and apparent optical properties in shallow lakes, the case of Taihu Lake
No full textThe spectral distribution of downwelling solar irradiance is an important factor in the radiative balance, primary productivity and biogeochemistry in most lakes. In the present study, we show the relative importance of different inherent and apparent optical properties in controlling the spectral attenuation of diffuse downwelling irradiance in a large shallow lake in eastern China. Most importantly, we show how elevated concentrations of suspended matter not only increase attenuation but are linked to a “spectral shift” in major attenuation peaks, with important consequences on biogeochemical processes and remote sensing. The analysis of the lake optical properties in relation to the geographical distribution of submersed macrophytes indicates how heterogenic optical conditions play a role in controlling benthic primary production
Modelling energy fluxes in remote wetland ecosystems with help of remote sensing
No full textThe study of the material and energy fluxes that characterise an ecosystem is fundamental to understanding the
behaviour of that system and its resiliency in the face of changing local and global conditions. In the present research,
an extended energy balance model was used to examine the fluxes that characterise the energy exchange between a
large wetland area and its environment. For each flux term, a number of modelling approaches was compared.
Modelling was complemented through the use of irradiance measurements from satellite data. The model output
shows the daily and season variations in each energy term, as well as a comparison of the modelling approaches. The
final output of the model is validated with the measured hourly variation in the enthalpy (water temperature) of the
lagoon. A comparison is made of the relative importance of each energy term in the overall balance of the system.
This physical based model is being used to examine possible modifications of local and global environments to the
wetland energy balance. The model is also being combined with fauna models to examine the relation between climate
and population characteristics (habitat). The present work is directed towards the study of a subtropical lagoon in the
internationally important wetland, the Esteros del Ibera in Argentin
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