Impact Of Dredged Grounds Dumping
IMPACT OF DREDGED GROUNDS DUMPING
ON CHANGES IN COMPOSITION OF SEA WATER
TAKEN FROM THEIR MAIN BURIAL PLACES
O.A. Petrenko
Southern Scientific Research Institute of Marine Fisheries and
Oceanography (YugNIRO), Kerch, Ukraine
A particular distribution in the Black Sea area has been given to such type of anthropogenic activity as dumping of dredged grounds. It is connected, in the first instance, with the necessity to support artificially the port areas on the Black Sea coasts in the condition available for the exploitation [3], therefore the largest acting dumps of grounds are located in the vicinity of large ports. As an example Odessa and Danube dumps of grounds may be taken as well as underwater dumping of dredged grounds in the Kerch Strait area aside the Black Sea.
Grounds in the underwater dumps in the area between the Dnieper and Danube have been dumped at least since the beginning of the twentieth century. According to the archive data of the Research Institute ChernomorNIIproekt, up to 5.0 million m3 of grounds have been buried since 1963 till now [4]. Merely during the construction of the port «Yuzhny» (1974-1982) the amount of dumped grounds varied within the range 0.229-3.744 million m3 or 0.4-6.3 million tons of ground. The mentioned amount of dumping is comparable with the summary amount of solid outflow of the Dnieper and Bug - 2.3 million of tons per year. Since 1980 the dump in the Danube estuary began to be exploited with the amount from 1.3 million m3 (1980) to 2.66 million m3 (1985).
Monitoring in the area of the Odessa and Danube dumps of grounds [1] revealed that the main contribution to pollution of the ecosystem of the north-western Black Sea is made by organic and biogenic substances. The coastal zone of the north-western Black Sea faces, even besides dumping of grounds, constant and increasing pressure of anthropogenic eutrophication, resulting in eruption of ecosystem homeostasis [1]. During throwing of grounds into dump the high concentrations of nitrogen and phosphorus compounds turning from
grounds to water evoke the excessive growth of phytoplankton in the adjacent areas (1.5-2 times much than average values for many years for the period of 1956-1983). That stipulates the great over-saturation of water with oxygen (up to 200-250%) on the surface and intensive consumption of oxygen near the bottom after death and sinking down of algae. The weak mixing of waters in summer aggravates the process of hypoxy in the near-bottom layer.
In Kerch region till recently dumps of grounds are located immediately in the strait and pre-strait shallow zones [4]. The amount of dumped grounds in buried places varied from 1.0 to 5.0 million m3. Since 1987 with transition of dump into the pre-strait area of the Black Sea the amount of dredging reduced and now it is not exceeded 1.0 million m3 annually, that is evidently connected with significant increase in cost of production and utilization of each cubic meter of ground [5].
Monitoring carried out by YugNIRO specialists since exploitation of acting deep-water dump, revealed that the main factors of impact on the coastal zone ecosystem are both merely mechanical reasons resulting in mudding of fishing spots and toxic effects associated with instant increase in content of pollutants in the grounds subject to dredging. In this connection in complex approach to assessment of marine environment based on observations over hydrological, hydrochemical and hydrobiological parameters, one of the leading roles is given to the control of the level of water contamination and contamination of bottom sediments with the most toxic for water organisms matters – such as heavy metals, oil components and chlorine organic compounds [5].
Pelite particles make from 30 to 50% of amount of dumped grounds (diameter 0.01 mm and less), able to hydratation and shift for large distances. During the summer stratification washed away pelite masses concentrate in the layer of temperature leap in the depth of 15-20 m, screening the sun rays and having the negative impact on photosynthesis processes of bottom plants. Along with the mentioned processes, the expansion of the area subject to anthropogenic contamination with toxic matters takes place owing to re-distribution of muds in the place of deep-water dump, stipulated both by anthropogenic (dumping of dredged grounds) and natural reasons (under the impact of dynamic factors) [2]. All these are characteristic of accumulation of pollutants in bottom sediments in the area of acting dump of grounds in concentrations exceeding the background (control) values [6].
Monitoring of the level of contamination of the area of underwater dump of grounds for the period of its functioning (since 1987) demonstrated that, to the largest extent, mercury, lead and oil transformed components (tar and asphaltene) are accumulated in bottom sediments. As a result, the content of mercury in the grounds taken from the central part of the dump have increased as much as twice (from 0.05 to 0.10 mkg/g of the dry matter), and in the water taken from the near-bottom layer have reduced slightly (from 0.22 to 0.10 mkg/l, that is stipulated by the migration of the mentioned element in the system bottom sediments - water. Lead maximum concentrations (up to 21,5- 37,7 mkg/g of the dry matter) are met in the central part of the dump and in the zones with the increased content of fine disperse mud fractions in the bottom sediments. The content of lead in water has increased from 0.54 to 5.83 mkg/l, that has been the consequence of the secondary pollution.
The summary content of oil products in the process of dumping has increased both in the bottom sediments and in the water of the near-bottom horizon (up to 2,3 times) with simultaneous changes in fractional composition of oil products: within the larger part of the area under review non-volatile slightly transformed hydrocarbons, evidencing the fresh inflow of oil into the area of the dump.
In this connection oil hydrocarbons and heavy metals from the dredged grounds, accumulating in bottom sediments, create the situation of «chronic» pollution of water masses and bottom sediments within the area and may serve the source of secondary pollution of the near-bottom layer of water.
Thus, increase in the share of prior pollutants in bottom sediments and in waters taken from the area under review in the process of dumping of dredged grounds is stipulated not only by natural processes (accumulation, transformation), but also by their anthropogenic contribution with dredged grounds. Moreover, anthropogenic components is predominant, that is proved by the fact of «chronic» (during 1990-1998) excess of legally allowable standards in water and geochemical background in bottom sediments for a number of pollutants.
References
1. Vasileva V.N., Vitrichenko E.E., Petrenko O.A., Sudiev R.A., Shiman M.Yu. Modeling of shift of non-conservative substances in Odessa Bay and in adjacent areas. Proceedings of GOIN, issue 203. Moscow: Gidrometeoizdat, 1992 - p. 16-33 (in Russian).
2. Vorontsova L.N., Petrenko O.A. Impact of burial of grounds on fish stocks in the Kerch Strait. In volume: Proceedings of the international scientific conference »Dredging, dumping and protection of water ecosystems" – 1993. Moscow: Interinstitutional Ichthyological Commision, p. 3 (in Russian).
3. Petrenko O.A. Results of modeling of the process of dissemination of the weighed substances on location during dredging. - 1994. Proceedings of YugNIRO, vol. 40 - Kerch: YugNIRO Publishing, p. 31-35 (in Russian).
4. Petrenko O.A., Sebakh L.K., Pankratova T.M., Avdeeva T.M., Popova T.V. Dumping of grounds and its impact on distribution of pollutants in the Kerch pre-strait area of the Black Sea. - 1993. In: Theses of reports at 9th conference for commercial oceanology. Kaliningrad: AtlantNIRO, p. 314-316 (in Russian).
5. Petrenko O.A., Sebakh L.K. Methodological prereqisites for the arrangement of environmental monitoring of the sea in the area of dumping of dredged grounds. - 1994. YugNIRO Proceedings, vol. 40 - Kerch: YugNIRO Publshing, p. 36-37 (in Russian).
6. Sebakh L.K., Pankratova T.M., Petrenko O.A. anthropogenic changes in marine environment under the impact of ground dumping in the process of dredging in the Kerch pre-strait area of the Black Sea. - 1998. YugNIRO Proceedings, vol.44, Kerch, YugNIRO Publishing, p. 40-47 (in Russian).
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