Current concentrations of heavy metals in the components of marine ecosystem as background monitoring level of oil-gas development at the Barents Sea shelf Печать E-mail

ILYIN G.V. Murmansk Marine Biological Institute RAS

Exploration of oil-gas fields on the shelf, oil products transportation even if all technological processes are well organized do not exclude a possibility of worsening the marine aquatic environment quality and biota state.

Among different pollutants (oil hydrocarbons, PAH, PCB), entering the marine environment from the technogenous sources, there appear also heavy metals and micro-elements. Negative impact of the economic activity of the man on local parts might be spread quickly in the aquatic environment, like it is shown on the example of oil spots drift (Zuev, Ilyin, 1996). While analyzing the degree of contamination of migrating actively hydrobiontes, fishes in particular, integrity of the large marine ecosystem is expressed with special precision.

Current background of heavy metals and micro-elements concentrations in the components of the sea ecosystem is formed by the summary impact of the continental run-off of metals, eolic transportation, advection by trans-boundary currents (Ilyin, 2001). Increase of their contents in the environment might occur due to the technogenous impact. Entering the organism of hydrobiontes metals are capable to be accumulated in the liver, kidneys, muscles and if the concentration is increased this might lead to their pathology.

Thus considering fishery activity significance of the Barents Sea, control of heavy metals concentrations in the environment and in the organisms of hydrobiontes must become one among the major components of complex monitoring.

Southern part of the Barents Sea endures significant affect of the Kola Peninsula on the metals contents in water and in bottom sediments. The peninsula territory is rich in iron, copper-nickel, rare-earth ore provinces, due to which natural contents background of copper manganese, nickel, iron, aluminum in the fresh water run-off is raised (Dauvalter, 1998). In the mouth areas of the Pechenga, Kola, Patosoiki rivers Fe, Mn, Zn, Cu concentration in 60 % of observations is 2-6 times as higher as total allowable concentrations for the water in the fishery basins (List. 1999: State, 2001). In the eastern areas in the в реках Teriberka, Voron'ya, Iokan'ga rivers water quality is characterized by a high contents of Zn (up to 3.5 TAC), copper (1-7 TAC ) and iron (2-8 TAC ).

Central part of the sea is subjected by the impact of Nordcap and Murmansk coastal currents waters, transporting pollutants from the north- European sources, hi this part influence of atmospheric metal transport is expressed more clearly. Input of metals into the sea together with aerosols possesses seasonal variability connected with the changes of atmospheric circulation, melting cycles and formation of floating ice cover, hi winter together with the enforcement of the southern component of atmospheric transfer, metals concentrations in aerosols become 2-5 times higher in comparison to summer (Matishow Golubeva, 1998).

Heavy metals and micro-elements in water. Nowadays heavy metals do not create upon the whole high concentrations in water. Except iron and copper low concentrations remain in both: surface and lower water layers. But distribution over the area is not even. Distribution of iron, lead, cobalt, copper is characterized by the well expressed mosaic character.

For cobalt and manganese increase of concentrations in coastal zone is typical. Continental run- off is of the determining significance for the enrichment of coastal waters with these metals (Biotesting.... 2003).

In copper distribution there distinguished two areas of the increased concentration close to the total allowable concentration (5.0 mkg/1) these are - coastal zone and the area of the polar frontal zone, hi coastal zone copper concentration is determined by the influence of coastal run-off. In the zone of polar front in the northern periphery of Central Trough copper increase in summer might be caused by ice cover melting, accumulated in winter atmospheric fall-out.

On the background of low concentrations of other metals iron contents on the surface and near bottom layers in summer exceeds TAC for the fishery basins (50 inkg /1).

Mercury and cobalt are observed in the water over the greater part of the territory in the concentrations lower that the detection limit. Significant concentrations of these elements were noted in the Kola bay waters that are in the area of the intensive technogenous impact. In the mouthpart of the bay mercury contents varied in the range 0-0.057 mkg/1. In the waters of the inner area in singular samples high mercury concentrations - up to 4.0 mkg/1. Cobalt concentrations in the water varied in the range 0.05-0.98 mkg/1. In contrast to mercury the higher contents of cobalt occurred mouthpart of the bay.

It is quite reasonable to note the tendency of growth of mercury concentrations during flooding period caused by spring snow melting or autumnal rains. Cobalt concentrations growth is more pronounced during ice cover formation in the fresh-water watercourses, in the period when the stock is small. It might be presupposed that mercury input into the sea takes place due to the wash out of atmospheric fall-out from the watershed territory.

Cobalt input occurs probably due to the soils layers drainage mainly at the change of water balance and redox-conditions in the soils.

Arsenic in seawater is discovered in the amount the order as lower as the TAC. The highest concentrations of this element are noted in the coastal areas.

Heavy metals and micro-elements in bottom sediments, Metals contents in bottom sediments reflects the tendencies of the prolonged period. But in the coastal areas when the depths are not large periodic and constant currents play a very significant role as they rewash and re-sediment sediment, transport mineral and organic ad-mixtures entering with the coastal run-off.

Practically all metals in bottom sediments are concentrated in relation to aquatic environment. Iron, cadmium, lead, zinc, chrome, copper, nickel, arsenic are united by the general regularity, characterized by localization of maximal concentrations in the Central trough sediments. Pointed out regularity was noted earlier and is quite probably of stable character (Iliyn, Petrov, 1994; Plotitsyna et al., 2002).

For highly toxic mercury and cobalt an opposite directed distribution tendency is typical. In the sediments of Central trough a low contents of these elements in contrast to those of the Murmansk shallow water area and coastal zone is registered. The largest mercury accumulation level was observed in the Kola bay sediments - up to 0.2 mkg/g dry sediment in the mouth part of the bay. In the sediments of other economically exploited bays - Motovsky bay and others, mercury accumulation was in places 0.10 mkg/g.

In the formation of copper, nickel, chrome, zinc, arsenic regularity accumulation the greater role probably plays atmospheric transfer and fall- out of aerosols to the surface of the floating ices. In the economically used Motovsky and Kola bays in contrast to other coastal areas parts high concentrations of these elements are also observed. Copper concentration in the sediments of some parts in these bays reached 40.0-45.9 mkg/g, that of nickel up to 40.4 mkg/g, chrome - 35-40.6 mkg/g dry sediment.

In the sediments of the coastal zone fresh-water water courses forming zones of geochemical barriers and intensive sedimentation play a significant role in the localization the areas where increased metals accumulation is observed. Iron, manganese, nickel, chrome in the raised amounts were concentrated in the sediments of the Pechora run- off distribution.

Accumulation of micro-elements in the hydrobiontes tissues. Having entered the aquatic environment micro-elements start to be included into the biogeochemical cycles. Teclmogenous increase of their concentrations in the environment- caused by discharges by drilling solution or other teclmogenous substances, conditions transport micro-elements into toxic elements and their accumulation in the hydrobiontes organisms. In connection with this there appears a question how this background of micro-elements is reflected in the hydrobiontes contamination including fishes which constitutes the basis of Barents sea bioresources?

Investigations earned out by Murmansk Marine Biological Institute during several years gives the impression on some regularities of heavy metals accumulation in the tissues of hydrobiontes belonging to different groups in the Barents Sea.

Sestonphagous coelenterata are capable of concentrating in themselves the metals several times as greater as other benthos animals. Inhabiting in the Pechora sea Alcyonidium diskiforme (Briozoa), Actinia sp., Spongia sp. accumulated chrome, lead, cobalt, manganese, arsenic and iron in greater amounts, than other invertebrates. Maximal concentrations of these metals are discovered in the tissues of seston- phagous from the Pechora river fresh-water run- off distribution area: Pb - 0.51; Cr - 4.8; Co - 1.5; Mn - 133; As - 2.56 mg/kg wet weight. Echinodemis (Ophyiura sarsi, Stegohyiura nodosa, Asterias rubens, Strongylocentrotus droebachiensis) in this area selectively accumulate zinc and tin. Specimens of these species inhabiting to the west, in the zone of White Sea current waters distribution area cadmium and mercury are accumulated in the raised concentrations (up to 0.06 mg/kg and 0.16-0.17 mg/kg wet weight, correspondingly).

In fishes muscles nickel, chrome, cobalt contents is below the limits of discovery by the methods applied. Lead, cadmium and mercury accumulation varied in the very narrow range and evidently, to the great degree corresponds to the natural background level. The most contrast differences between pelagic and demersal species might be noted in zinc contents. Lapelin, pollack herring accumulate it twice as much mat other species, borne demersal fish species mainly of benthos type of feeding: catfishes, long rough dab, lump-sucker possess the property to accumulate copper and zinc in greater amounts that other species. Raised accumulations of these metals is a distinguished feature of prawn. On the example of echinoderms group the explanation to this phenomenon is to be found not only in the type of feeding but also in the location of the inhabitancy areas where the specimens have been caught and in the environmental conditions.

Spatial differences in metals accumulation on the example of cod are presented on figure. Fishes caught in the eastern fishing grounds accumulate copper to a greater degree whereas they accumulate very little mercury. For the coastal areas raised accumulation of all metals especially mercury and lead is typical. For western sea margins and for the waters of the Atlantic origin sea upon the whole relatively high contents of arsenic in cod muscles is peculiar.

Pelagic fishes - polar cod, capelin, navaga inhabiting in the eastern part of the sea do not practically differ as for micro-elements accumulation in their tissues. Bottom fishes inhabiting in the areas of the perspective oil fields, for instance, Arctic [polar] staghom sculpin accumulate chrome, nickel and iron in much greater concentrations. This is a more settled species and depends to a greater extend on the ecological state of the area of inhabitancy in comparison to pelagic species. Other demersal species: long rough dab, plaice, cod caught in the Kolguev fishing ground are distinguished by relatively increased accumulation of mercury in the tissues.

Another example of territory differentiation in heavy metals accumulation by hydrobiontes might become a Red King crab. Practically all heavy metals are accumulated in crab's muscles in significantly greater amounts that in other commercial hydrobiontes. Raised metals concentration level is explained by the fact that the crabs are caught in the coastal zone in the vicinity of the technogenous contamination sources zone - the Kola and Motovsky bays. For the crabs inhabiting in the Kola bay raised mercury and lead accumulation is especially typical. In the Motovsky bay the crabs accumulate arsenic and copper.

In the south-eastern sea another species of crabs, Hyas araneus occurs, hi the Pechora Sea in the muscles copper and tin are accumulated mainly. And the specimens caught near the Kolguev island are characterized and distinguished by abnormally high mercury concentrations in the tissues - 1.31 mg/kg wet weight.

Thus, there exists a little investigated problem of micro-elements anthropogenic discards into the Barents Sea. It became evident that separate fish species and hydrobiontes possess selectivity in metals accumulations, and spatial inequality of micro-elements accumulation by hydrobiontes might reflect the degree of anthropogenic pressure on the areas of sea area. Additional technogenous load conditioned by oil-gas complex development on the Barents sea might lead to the growth of metals concentrations in the fishes on separate fishery grounds level. To guarantee effective complex monitoring process heavy metals are to be considered as one of the major directions for the investigations.

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