Quantification of sediment-water interactions in a polluted tropical river through biogeochemical modeling

Diagenetic modeling presents an interesting and robust way to understand sediment-water column processes. Here we present the application of such a model to the Day River in Northern Vietnam, a system that is subject to high levels of domestic wastewater inputs from the Hanoi metropolitan area. Experimental data from three areas of different water and sediment quality, combined with some additional data from the river, are used to set up and calibrate a diagenetic model. The model was used to determine the role of the sediments as a sink for carbon and nutrients and shows that in the dry season, 27% of nitrogen, 25% of carbon, and 38% of phosphorus inputs into the river system are stored in sediments. The corresponding numbers during the rainy season are 15%, 10%, and 20%, respectively. The diagenetic model was then used to test the impact of an improvement in the treatment of Hanoi's municipal wastewater. We show that improved wastewater treatment could reduce by about 17.5% the load of organic matter to the sediment. These results are the first to highlight the importance of sediments as a potential removal mechanism of organic matter and nutrients from the water column in this type of highly impacted tropical urban river, further demonstrating that rivers need to be considered as reaction sites and not just as inert conduits

Імітаційне комп'ютерне моделювання процесу організації підприємницького інноваційного центру за допомогою програмного пакету «Ithink»

В статті робиться спроба розробки та застосування імітаційної моделі створення підприємницького інноваційного центру з метою поширення переваг і можливостей інноваційної діяльності в регіональній економіці. Для розробки імітаційної моделі використовується пакет програмного продукту «Ithink», який став широко застосовуватися в моделюванні різноманітних економічних процесів в економіці і якій дозволив створити робочі моделі таких процесів, враховуючи різнобічні фактори впливу на вказані процеси та визначити наслідки їх дії з послідовним корегуванням та відпрацюванням самих моделей в реальній практиці.The article is aimed to propose a simulating model of the creation of the innovational regional center to examine the advantages and innovational possibilities in the regional economy. The popular software “I think” which has become widely used in modeling different similar economic processes, is used for the development of the simulation model. This gives the possibility to take into consideration various factors of influence on these processes and calculate their consequences with the option of their gradual correction and working out the models in the real practice

Water residence time : A regulatory factor of the DOM to POM transfer efficiency

The pools of dissolved (DOM) and particulate organic matter (POM) and of transparent exopolymeric particles (TEP) were studied along two sampling gradients in the lagoon of New Caledonia in relation to the residence time of the water masses. The efficiency of the transfer of material from the dissolved to the particulate phase via TEP formation, indicating the physicochemical reactivity of organic matter, was investigated. DOM, POM, and TEP concentration increased along the sampling gradients, but their relative proportions varied. The contribution of the TEP pool to POM increased from 20% to 60%, from the most oligotrophic stations to the more anthropogenically affected bays. According to the low density of TEP and to the observed variations of the proportion of TEP compared with more conventional and solid particles, the aggregates formed inside the bays would be either neutrally or positively buoyant, whereas in the vicinity of the coral barrier, they would be negatively buoyant. As a result, the downward export of organic matter inside the bays might be greatly reduced, thereby prolonging the residence time of organic matter in the water column. The efficiency of the DOM/TEP transformation and the TEP turnover rate dropped drastically when the residence time increased from 0 to 50 d, suggesting that the reactivity of organic matter is reduced as it ages. The very high residence time of the water mass inside the bays, constrained by the hydrodynamic circulation inside the lagoon, favors the installation of a feedback system in which organic matter is not exported and is continuously degraded, leading to the formation of refractory DOM with a low physicochemical reactivity. In contrast, organic matter produced in areas in which water mass has a low residence time (i.e., near the coral barrier) is rapidly exported because of its high physicochernical reactivity

A short review of fecal indicator bacteria in tropical aquatic ecosystems : knowledge gaps and future directions

Given the high numbers of deaths and the debilitating nature of diseases caused by the use of unclean water it is imperative that we have an understanding of the factors that control the dispersion of water borne pathogens and their respective indicators. This is all the more important in developing countries where significant proportions of the population often have little or no access to clean drinking water supplies. Moreover, and notwithstanding the importance of these bacteria in terms of public health, at present little work exists on the persistence, transfer and proliferation of these pathogens and their respective indicator organisms, e.g., fecal indicator bacteria (FIB) such as Escherichia coli and fecal coliforms in humid tropical systems, such as are found in South East Asia or in the tropical regions of Africa. Both FIB and the waterborne pathogens they are supposed to indicate are particularly susceptible to shifts in water flow and quality and the predicted increases in rainfall and floods due to climate change will only exacerbate the problems of contamination. This will be furthermore compounded by the increasing urbanization and agricultural intensification that developing regions are experiencing. Therefore, recognizing and understanding the link between human activities, natural process and microbial functioning and their ultimate impacts on human health are prerequisites for reducing the risks to the exposed populations. Most of the existing work in tropical systems has been based on the application of temperate indicator organisms, models and mechanisms regardless of their applicability or appropriateness for tropical environments. Here, we present a short review on the factors that control FIB dynamics in temperate systems and discuss their applicability to tropical environments. We then highlight some of the knowledge gaps in order to stimulate future research in this field in the tropics

Production of individual marine organic aggregates using paramagnetic microspheres : a new tool for examining microbial associations with aggregates

We describe a new method to produce marine aggregates from natural organic material based on the sticking properties of transparent exopolymeric particles. Seawater samples were prescreened and ultrafiltered to concentrate the 30 kDa to 10 mu m size fraction. First, we produced small magnetizable aggregates by combining glass microfibers and paramagnetic 1-mu m beads with the organic matter present in the concentrated solution. The second step involved clustering the small aggregates into a single macro-aggregate, using a small ring-shaped magnet as an aggregation nucleus. Viral and bacterial densities, determined after dissolution of the newly formed aggregates with methanol, averaged 13.8 x 10(6) +/- 3.6 x 10(6) vir. agg.(-1) and 4.1 x 10(6) +/- 1.1 x10(6) bact. agg.(-1). Bacterial respiration and production measurements of single aggregates averaged 8.47 +/- 1.72 nmol O-2 agg.(-1) h(-1) and 1.54 +/- 0.45 ng C agg.(-1) h(-1), respectively. Particulate organic carbon and nitrogen content of the newly formed macro-aggregates averaged 31.92 +/- 2.67 mu g C agg.(-1) and 3.44 +/- 0.43 mu g N agg.(-1), respectively. This approach allows the concentration and isolation of the organic matter precursors that compose natural aggregates and provides a simple protocol for recombining those precursors into single newly formed macro-aggregates, which can then be easily manipulated for further investigation. This method is a new tool for investigations into the interactions between microorganisms and marine aggregates and their implications at the ecosystem level, but also into the interactions between aggregates and dissolved organic or inorganic substances

Transparent exopolymer particles and dissolved organic carbon production by Emiliania huxleyi exposed to different CO₂ concentrations: a mesocosm experiment

The role of transparent exopolymer particles (TEP) and dissolved organic carbon (DOC) for organic carbon partitioning under different CO2 conditions was examined during a mesocosm experiment with the coccolithophorid Emiliania huxleyi. We designed 9 outdoor enclosures (similar to11 m(3)) to simulate CO2 concentrations of estimated 'Year 2100' (similar to710 ppm CO2), 'present' (similar to410 ppm CO2) and 'glacial' (similar to190 ppm CO2) environments, and fertilized these with nitrate and phosphate to favor bloom development. Our results showed fundamentally different TEP and DOC dynamics during the bloom. In all mesocosms, TEP concentration increased after nutrient exhaustion and accumulated steadily until the end of the study. TEP concentration was closely related to the abundance of E. huxleyi and accounted for an increase in POC concentration of 35 +/- 2 % after the onset of nutrient limitation. The production of TEP normalized to the cell Abundance of E. huxleyi was highest in the Year 2100 treatment. In contrast, DOC concentration exhibited considerable short-term fluctuations throughout the study. In all mesocosms, DOC was neither related to the abundance of E. huxleyi nor to TEP concentration. A statistically significant effect of the CO2 treatment on DOC concentration was not determined. However, during the course of the bloom, DOC concentration increased in 2 of the 3 Year 2100 mesocosms and in 1 of the present mesocosms, but in none of the glacial mesocosms. It is suggested that the observed differences between TEP and DOC were determined by their different bioavailability and that a rapid response of the microbial food web may have obscured CO2 effects on DOC production by autotrophic cells

Artificial neural network analysis of factors controling ecosystem metabolism in coastal systems

Knowing the metabolic balance of an ecosystem is of utmost importance in determining whether the system is a net source or net sink of carbon dioxide to the atmosphere. However, obtaining these estimates often demands significant amounts of time and manpower. Here we present a simplified way to obtain an estimation of ecosystem metabolism. We used artificial neural networks (ANNs) to develop a mathematical model of the gross primary production to community respiration ratio (GPP:CR) based on input variables derived from three widely contrasting European coastal ecosystems (Scheldt Estuary, Randers Fjord, and Bay of Palma). Although very large gradients of nutrient concentration, light penetration, and organic-matter concentration exist across the sites, the factors that best predict the GPP:CR ratio are sampling depth, dissolved organic carbon (DOC) concentration, and temperature. We propose that, at least in coastal ecosystems, metabolic balance can be predicted relatively easily from these three predictive factors. An important conclusion of this work is that ANNs can provide a robust tool for the determination of ecosystem metabolism in coastal ecosystems

История формирования календарной лексики в персидском языке

Основная цель данной работы заключается в выявлении корней современной персидской календарной лексики, для чего следует проследить историю календарных систем Ирана, выявить их характерные черты с точки зрения лексики и определить современное состояние календарного пласта в персидском языке