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Estuarine specific transport and biogeochemically linked interactions for selected heavy metals and radionuclides


Previous work in Arctic marine and Siberian reverie systems has provided science with some of the tools necessary to model the transport of contaminants from inland sources to the open sea. The picture, however, is incomplete because unimportant link in the system, i.e. the marine-freshwater interface, has received little attention in the past. This project aims to redress this balance with the main objective of modelling the biogeochemical behaviour and impact (man and environment) of selected radio nuclides and heavy metals in the Hennessey Estuary. This will be achieved primarily through (a) collation of data relevant to marine modelling; (b) field studies for the purpose of model parameterisation and the identification of biogeochemical reactions; (c) development of new and existing transport models. The result will be a set of tools which can be used to determine the behaviour and fate of selected contaminants in a large Siberian estuary.
The project has been largely successful in addressing project objectives. All deliverable reports have been completed and submitted to the EU. Progress has been made within several scientific areas. Three successful field expeditions were held during the project duration. This includes work on board the R/V Akademik Boris Petrov in the summers of 2000 and 2001 and additional terrestrial field campaigns conducted on areas affected by ocean land interactions in 2001 and 2002. Our understanding of the short-term behaviour of radionuclides in the aquatic Yenisey estuarine system has developed markedly within the last few years through the analyses of samples and the simulation work undertaken using different modeling tools. For example, tangential flow ultrafiltration techniques have been used to explore the significance of radionuclide transport in colloidally bound form. The colloidal fraction of Pu is significantly higher than the levels recorded earlier for open Arctic sea areas. Low 240Pu/239Pu atom ratios were generally observed in association with dissolved phases (colloids and low molecular mass species) and higher ratios were observed in association with particulate phases.

It was also established that high molecular mass dissolved humic compounds are prone to flocculation and subsequent sedimentation at the freshwater-saltwater interface in the Yenisey Estuary. An inverse relationship was observed between salinity and dissolved organic carbon (DOC). Within the DOC pool, high molecular mass colloids appear to be prevalent and may therefore strongly influence the transport of contaminants within this system. Field observations showed that vertical salinity and temperature gradients in the Yenisey Estuary can be very sharp and occur when strong off-shore surface flows lead to the penetration of high saline waters into the estuary. Results from the "HAMSOM" model show that the south-westward bottom current along the Tamyr coast is very persistent during the summer months and that this flow may be responsible for carrying saline water towards the Yenisey Estuary, thus enhancing vertical stratification. A pool of saline water formed from this source, in front of the estuaries, may then feed a bottom flow that penetrates the estuary as a "salt intrusion". Russian experts were able to identify the conditions necessary for the formation of a salt intrusion whereby enhanced surface offshore transport is compensated by an on-shore near bottom flow that penetrates into the estuary. Sediments deposits have been extensively studied during the project duration. Heavy metal and radionuclide contamination levels have been well documented along with concomitant information on lithology (mineralogy and grain-size) and sedimentation rates. Heavy metal studies included estimation of the riverine contribution to Kara sea bottom sediments and revealed additional technogenic sources of contamination based on trace element concentrations in sediments. Activity of Pu radionuclides in sediments increased in the inner estuary zone leading to the preliminary conclusion that a river-derived Pu source exists. Cs-137 vertical distribution in sediments enables reconstruction of historic releases from different radiochemical enterprises. Recent data (2001-2002) on Cs-137 concentrations in top layers of bottom sediments proves its significant decrease due to radioactive decay and the new deposition of less contaminated sediments. This indicates that KMCC has ceased to be the active source of radionuclide contamination in the Yenisey Gulf. Terrestrial investigations performed provided additional information on the radionuclide and heavy metal distributions in floodplain and coastal areas depending upon site location, distance from the sea and site-specific geomorphological and lithological features related to the recent history of the studied areas.

A large amount of new information has been generated on biota present in the estuary looking, for example, at aspects of biodiversity, structure and biomass of benhtic communities and the utilization of different biological resources for man. Bottom communities have not revealed any significant changes since the time of previous studies carried out in the early 1990s. Some changes recorded in the bottom community composition, biodiversity and biomass are within the range of natural phenomena occurring in the sea. Data have been compiled on levels of radionuclides and heavy metals in biological components of both the terrestrial and aquatic food-chains and models have also been applied to simulate behaviour of radionuclides in some of these food-chains. Results from basic impact assessment undertaken within this project have suggested that the impact of both heavy metals and radionucldies on man and the environment can be considered negligible in most cases.


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13,grini naeringspark
1345 Osteras

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