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Arsenic distribution in sediments of the Mirim-Patos lagoonal system is investigated. Deposits of fresh water Mirim Lagoon and those of the fresh water part of the Patos Lagoon contain 2.5 and 7.7 mg kg(-1), respectively, on average of total arsenic. In contrast, estuarine sediments of the Patos Lagoon are evidently contaminated by arsenic in high concentrations (up to 50 mg kg(-1)), and about 80% of the arsenic there is found in a bioavailable form. Analytical data coupled with direct, visual observations of estuarine water contamination by raw phosphorites and fertilizers suggest that the major source of arsenic in the estuarine sediments originated from the fertilizer industry. 相似文献
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Present study has continued the investigation on distribution of mercury in estuarine sediments of Patos Lagoon which began whilst assessing the after-effect of enormous accidental discharge of sulfuric acid into the estuary. An attempt to evaluate the contribution of anthropogenic effluents on mercury pollution in sediments was undertaken. The effluents from Rio Grande City sewages were categorized into four groups based on their sources. Comparison of mercury concentrations from those, indicated that domestic effluent was prevalent. Apparent geographic controls of effluent locations enriched in mercury on zones of polluted estuarine sediments were also revealed. Insufficient control on waste collecting and absence of sewage treatment are considered the principal causes of mercury pollution in estuarine sediments. 相似文献
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We consider the problem of year-round cooling of water-saturated soil to freezing temperatures in order to convert it into a state of permafrost.A new soil-cooling apparatus is proposed.The apparatus is to be made in modular form and connected to passive-active thermal piles (thermosyphons).The estimated capacity of one apparatus allows simultaneous use of up to 1,000 thermal piles for ground freezing.The apparatus is based on natural sources of energy:solar radiation and wind;and it can be used for soil freezing.This approach can prevent thawing of soft soils under railways and roads,as well as under buildings or structures,in an area of more than tens of hectares.The apparatus has no mechanical moving parts and can operate for a long time in stand-alone mode without staff involvement. 相似文献
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Nicolai S. Panikov 《Polar research》1999,18(2):237-244
This review covers selected aspects of recent international efforts to measure and model greenhouse gas emission from northern wetlands, to identify the environmental factors that control gas emission, and to investigate wetlands'responses (particularly with respect to gas emission) to global change. Both bottom-up and top-to-bottom approaches, based respectively on local observations plus inventory of gas fluxes and inverse modelling of global circulation, agree on the size of the high latitude (>60° N) contribution to global methane, which should be about 13% or 70 Tg/year. It has been shown that winter and spring fluxes are an essential part in the annual budget of CH4 and especially CO2 exchange (varying from 5 to 50%). Soil micro-organisms were shown to be able to respire during winter even at-16° C. In comparison to aerobically respiring organisms, anaerobic methanogenic bacteria were less active in frozen soil, although they are subjected to significant stimulation by soil freeze-thaw cycles. The absence of immediate coupling of methanogenesis with plant photosynthesis implies that substrates for methane formation are derived from peat decomposition rather than from root exudation. 相似文献
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Nicolai Mirlean Paulo Baisch Marcelo P. Travassos Cristina Nassar 《Geo-Marine Letters》2011,31(1):65-73
Arsenic levels (up to 130 mg kg−1) substantially exceeding the official threshold have recently been documented in beach and nearshore sediments along more
than 50 km of coastline in the Brazilian state of Espírito Santo between 19°50′ and 20°12′S. In an attempt to assess the sources
of this enrichment, we performed a study on arsenic distribution in the main mineral substances and living organisms in the
beach environment. Laboratory tests on arsenic retention by beach carbonate debris have also been carried out. The data suggest
that sedimentary arsenic occurs largely bound to particles of the calcareous red alga Corallina panizzoi, whereby live specimens contained much smaller amounts of this metalloid than was the case for nonliving material (2.4 and
20.3 mg kg−1, respectively). Experimental tests confirmed the ability of C. panizzoi detritus to retain arsenic at pH intervals and ionic strength characteristic of seawater. There are two potential sources
of that metalloid for calcareous debris in sediments: brown macroalgae, which were found to contain high levels of As (up
to 66.3 mg kg−1), and ferruginized sandstones (up to 23.0 mg kg−1). We argue that any contribution of brown algae to beach sediment enrichment by As would be minor, and consider the ferrous
sandstones from coastal sedimentary rocks of the Barreiras Group as the principal large-scale source of arsenic in the marine
environment of Espírito Santo. The experimental data, together with field studies, corroborate the interpretation that arsenic
anomalies in sediments with calcareous debris can form when weathered continental rocks even only slightly enriched in As
are leached by marine waters, and the As is at least partially retained by biogenic calcareous detritus in nearshore sediments.
Considering that rocks of the Barreiras Group are exposed to marine erosion far to the north of Espírito Santo, we estimate
that marine sediments containing calcareous material are “anomalously” enriched in As along approximately 2,000 km of the
Brazilian tropical coastline. 相似文献
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Ruslan Melian Nicolai Myrlian Alexander Gouriev Constantin Moraru Frank Radstake 《Hydrogeology Journal》1999,7(2):188-196
This paper describes the results of a groundwater quality assessment conducted in two pilot areas, Balatina and Carpineni,
in the Republic of Moldova. Shallow groundwater is the main source of drinking water in rural areas, but reliable data on
its quality are currently insufficient for developing rural water-supply systems with standard designs. The main components
of the study included a field sampling program (including pesticides), an evaluation of the reliability of existing drinking-water
data, an analysis of land use and groundwater-pollution risks using GIS, and the formulation of recommendations to reduce
risks for public health.
Microbiological, nitrate, and selenium contamination are most serious in the villages. These contaminants should be given
priority in addressing drinking-water aspects for rural water-supply development in the two pilot areas. Pollution occurs
mainly due to poor sanitary conditions. In a few shallow wells, traces of selected pesticides were observed, but the effect
of these levels of pesticides on public health is still unclear.
Limited resources of shallow groundwater of good quality occur outside the villages. Additional pilot studies should be implemented
to prove the technical and institutional feasibility of developing and protecting these resources.
Received, September 1997 Revised, September 1998 Accepted, March 1999 相似文献
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Hermann Nicolai 《Journal of Astrophysics and Astronomy》1999,20(3-4):149-164
This contribution gives a personal view on recent attempts to find a unified framework for non-perturbative string theories,
with special emphasis on the hidden symmetries of supergravity and their possible role in this endeavor. A reformulation ofd =
11 supergravity with enlarged tangent space symmetry SO(1, 2) × SO(16) is discussed from this perspective, as well as an ansatz
to construct yet further versions with SO(1, 1) × SO(16)∞ and possibly even SO(1, 1)+ × ISO(16)∞ tangent space symmetry. It is suggested that upon “third quantization”, dimensionally reduced maximal supergravity may have
an equally important role to play in this unification as the dimensionally reduced maximally supersymmetricSU(∞) Yang Mills theory. 相似文献