Modeling the influence of eutrophication and redox conditions on mercury cycling at the sediment-water interface in the Berre Lagoon

This study presents a specifically designed Mercury module in a coupled benthic-pelagic reactive-transport model - Bottom RedOx Model (BROM) that allows to study mercury (Hg) biogeochemistry under different conditions. This module considers the transformation of elemental mercury (Hg(0)), divalent mercury (Hg(II)) and methylmercury (MeHg). The behavior of mercury species in the model is interconnected with changes of oxygen, hydrogen sulfide, iron oxides, organic matter, and biota. We simulated the transformation and transport of Hg species in the water column and upper sediment layer under five different scenarios, combining various levels of oxygenation and trophic state in the Berre lagoon, a shallow eutrophic lagoon of the French Mediterranean coast subjected to seasonal anoxia. The first scenario represents the conditions in the lagoon that are compared with experimental data. The four other scenarios were produced by varying the biological productivity, using low and high nutrient (N and P) concentrations, and by varying the redox conditions using different intensity of vertical mixing in the water column. The results of the simulation show that both oxidized and reduced sediments can accumulate Hg, but any shifts in redox conditions in bottom water and upper sediment layer lead to the release of Hg species into the water column. Eutrophication and/or restricted vertical mixing lead to reducing conditions and intensify MeHg formation in the sediment with periodic release to the water column. Oxygenation of an anoxic water body can lead to the appearance of Hg species in the water column and uptake by organisms, whereby Hg may enter into the food web. The comparison of studied scenarios shows that a well-oxygenated eutrophic system favors the conditions for Hg species bioaccumulation with a potential adverse effect on the ecosystem. The research is relevant to the UN Minimata convention, EU policies on water, environmental quality standards and Mercury in particular.publishedVersio

Bottom RedOx Model (BROM) general description and application for seasonal anoxia simulations

The details of biogeochemical transfer of matter at the sediment-water boundary were modelled by a one-dimensional C-N-P-Si-O-S-Mn-Fe vertical transport-reaction model for describing both the sediments and bottom boundary layers coupled with biogeochemical block simulating changeable redox conditions, and the carbonate system processes block. It was shown that seasonality in production and decay of organic matter significantly affects the redox conditions and the chemical species distributions and fluxes

Biogeochemical consequences of an oxygenated intrusion into an anoxic fjord

Background: This paper is based on the studies of the biogeochemical structure of the water column in the anoxic Fjord Hunnbunn (south-eastern Norway) performed in 2009, 2011 and 2012. This Fjord is an enclosed basin of brackish water separated by a narrow and shallow outlet to the sea with a permanently anoxic layer. We show how an oxygenated intrusion could lead to both positive and negative effects on the ecosystem state in Hunnbunn due to a change in the biogeochemical structure. Results: During the stratified periods in 2009 and 2012 the anoxic layer amounted to approximately 10% of the total water volume in the Fjord, while dissolved oxygen (DO) was present in 80-90% of the water. In the autumn of 2011 the water chemistry structure observed in Fjord Hunnbunn was clearly affected by a recent oxygenated intrusion defined by abnormal salinity patterns. This led to a shift of the DO boundary position to shallower depths, resulting in a thicker anoxic layer comprising approximately 40% of the total water volume, with DO present only in approximately 60% of the water. The oxygenated water intrusions led to a twofold decrease of the concentrations of hydrogen sulphide, ammonia, phosphate and silicate in the deep layers with a simultaneous increase of these nutrients and a decrease of the pH level in the surface layers. The concentrations of manganese, iron, and mercury species changed dramatically and in particular revealed a significant supply of iron and methylmercury to the water column. Conclusions: Oxic water intrusions into anoxic fjords could lead not only to the lushing of the bottom anoxia, but to a dispersal of sulphidic and low oxygen conditions to the larger bottom area. The elevation of the hydrogen sulphide to the shallower layers (that can be rapidly oxidized) is accompanied by the appearance in the subsurface water of methylmercury, which is easily accumulated by organisms and can be transported to the surrounding waters, affecting the ecosystem over a larger area

Mixing in the black sea detected from the temporal and spatial variability of oxygen and sulfide: Argo float observations and numerical modelling

-The temporal and spatial variability of the upper ocean hydrochemistry in the Black Sea is analysed using data originating from profiling floats with oxygen sensors and carried out with a coupled three-dimensional circulationbiogeochemical model including 24 biochemical state variables. Major focus is on the dynamics of suboxic zone which is the interface separating oxygenated and anoxic waters. The scatter of oxygen data seen when plotted in density coordinates is larger than those for temperature, salinity and passive tracers. This scatter is indicative of vigorous biogeochemical reactions in the suboxic zone, which acts as a boundary layer or internal sink for oxygen. This internal sink affects the mixing patterns of oxygen compared to the ones of conservative tracers. Two different regimes of ventilation of pycnocline were clearly identified: a gyre-dominated (cyclonic) regime in winter and a coastal boundary layer (anticyclonic eddy)-dominated regime in summer. These contrasting states are characterized by very different pathways of oxygen intrusions along the isopycnals and vertical oxygen conveyor belt organized in multiple-layered cells formed in each gyre. The contribution of the three-dimensional modelling to the understanding of the Black Sea hydro-chemistry, and in particular the coast-to-open-sea mixing, is also demonstrated. Evidence is given that the formation of oxic waters and of cold intermediate waters, although triggered by the same physical process, each follow a different evolution. The difference in the depths of the temperature minimum and the oxygen maximum indicates that the variability of oxygen is not only just a response to physical forcing and changes in the surface conditions, but undergoes its own evolution

Calculations and modelling environmental effects in Sælenvatnet caused by expansion of Sælenkanalen

I forbindelse med planleggingen av utvidelse av Sælenkanalen har det vært utført beregninger og modelleringer for å finne svar på hvilke effekter utvidelsen vil ha på miljøforholdene i Sælenvatnet. Som basis for arbeidet har Norconsults beregninger av maksimal økning av gjennomstrømning i kanalen på 20 % og hydrografiske målinger i Sælenvatnet gjennomført av NIVA i perioden 2010-16 blitt benyttet. Beregningene viser at kanalutvidelsen vil redusere den maksimale strømningshastigheten til under det halve av hva den er i dag slik at energien tilgjengelig for vertikal blanding av vannmassene i Sælenvatnet reduseres. Samtidig øker blandingseffektiviteten. Det innebærer at grenseflaten mellom oksygenholdig og oksygenfritt vann sannsynligvis påvirkes i liten grad. Modelleringer ved bruk av BROMmodellen ga samme konklusjon, dvs. at kanalutvidelsen i liten grad vil påvirke antallet tilfeller hvor H2S-holdig vann kommer opp til overflaten. En modellering med 400 % økning i horisontal blandingshastighet viste at grenseflaten mellom oksygenholdig og oksygenrikt vann ville heves med 0,1 0,7 m. Modelleringen er basert på måledata fra Sælenvatnet med data fra perioden 2010-14 inkludert da aeratoren (pumpen) var i drift, og dette kan ha endret den vertikale diffusiviteten i 0 til 10-15 m laget.The City of Bergen is planning a widening of the channel from Nordåsvatnet to Sælenvatnet where the deep water contains high concentrations of hydrogen sulphide (H2S). Norconsult has done calculations showing that the widening of the channel will increase the maximum inflow into Sælenvatnet by 20%. NIVA has done calculations and modelling to investigate the environmental effect of this increased inflow into Sælenvatnet. The conclusion is that the widening will have little effect on the conditions in Sælenvatnet.Bergen kommune, Vann- og avløpsetate

Stable isotope evidence for the bottom convective layer homogeneity in the Black Sea

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Plasma Technologies as the Basis for the Development of Russian Waste Processing

The article considers the current topic - justification of the possibility of organizing a system for recycling solid domestic and other waste based on plasma technologies and the subsequent use of secondary raw materials based on them. The current state of production sector of collection and disposal of solid domestic and other waste abroad and in Russia was analyzed. There are proposed a scheme of organization of solid domestic and other waste disposal system based on plasma technologies, operable at the under construction enterprise for processing of these wastes. The economic feasibility of this enterprise is justified. It was concluded that although the use of plasma technologies is most beneficial in the energy sector, when introducing plasma plants and creating solid waste disposal plants using these plants, taking into account the financial benefits in obtaining the raw materials and energy generated by them is not the main task, but an additional economic effect. The main thing is to reduce the negative impact of solid municipal waste on the environment and people

New Method of Oil Reservoir Rock Heterogeneity Quantitative Estimation from X-ray MCT Data

This paper considers a new method for “pore scale” oil reservoir rock quantitative estimation. The method is based on core sample X-ray tomography data analysis and can be directly used to both classify rocks by heterogeneity and assess representativeness of the core material collection. The proposed heterogeneity criteria consider the heterogeneity of pore size and heterogeneity of pore arrangement in the sample void and can thus be related to the drainage effectiveness. The classification of rocks by heterogeneity at the pore scale is also proposed when choosing a reservoir engineering method and may help us to find formations that are similar at pore scale. We analyzed a set of reservoir rocks of different lithologies using the new method that considers only tomographic images and clearly distributes samples over the structure of their pore space

A novel combined countercurrent chromatography – inductively coupled plasma mass spectrometry method for the determination of ultra trace uranium and thorium in Roman lead

International audienceThe concentration of uranium and thorium in lead shields, which are used in underground particle physics research, should be monitored at sub-ppt levels. A combination of extraction chromatography and inductively coupled plasma mass spectrometry can resolve this analytical task. However, a multi-step complicated separation procedure and clean room are required. Besides, the recovery yields for U and Th do not exceed 80% and 60%, correspondingly. We propose an alternative approach. U and Th were pre-concentrated and separated from Pb by countercurrent chromatography, which is a support-free liquid-liquid chromatography. A series of two-phase extraction systems were tested. Under the optimized conditions, U and Th were extracted using a system 1 M HNO3/0.01 M tetraphenylmethylenediphosphine dioxide in chloroform and then eluted by 0.01 M aqueous solution of etidronic acid and determined by inductively coupled plasma mass spectrometry. The separation is performed in one chromatographic run, takes less than 1 h, and provides the quantitative recovery of U and Th. The limits of detection are 3 and 1 ppt for U and Th, correspondingly. The concentrations of U and Th in Roman lead, which was raised from the sea bottom, were lower than the limits of detection. It sounds unbelievable, nevertheless, the antique lead manufactured by Romans can indeed serve as a high-purity low-background material for the construction of Pb shields. Apart from the analysis of antique lead, the proposed approach can be easily extended to the determination of ultra trace impurities in different materials due to a very wide variety of two-phase extraction systems, which can be used in countercurrent chromatography