Baltic Sea day 2007. Book of abstracts of 8th International Ecological Symposium (March 21-23, 2007, S.Petersburg). S.-Petersburg: 2007 Izdatelstvo Dialog. pp 119-120.
FilippovA.A., Kijko O.A., Lange E.K., Stogov I.A.
THE RESULTS OF TWO-YEAR LOCAL MONITORING OF HYDROBIOCENOSES UNDER IMPACT OF FERROMANGANESE NODULE EXTRACTION PROCESS IN THE EASTERN PART OF THE GULF OF FINLAND
The technological explorations of ferromanganese nodules in the Vyborg Bay (the Gulf of Finland) took place until 2005. In 2006 the commercial production of ferromanganese nodule deposits has started. During both the commercial production and technological exploration ecological surveillance was performed aimed to estimate the technological process impact on natural ecosystems.
In the course of nodule field exploration and subsequent commercial production the surface deposit layer was taken off, lifted to the dredge by suction-tube, washed-out and sorted-out at the system of sieves, and afterwards the sieved material (fine sediments) was dumped into water. Obviously this process should negatively impact the structure and function of benthic and pelagic biological associations in the region. The main types of ecological impact in the course of nodule extraction are the following (Filippov et al., 2006):
· Taking-off sediment upper layer
· Dumping of unused sediment fraction followed by:
· Increased amount of suspended matter in the water column
· Surface water enrichment by nutrients due to their income from dumped sediments
The increase of suspended matter concentration and corresponding turbidity elevation may lead to photosynthesis suppression and creation of unfavorable conditions for zooplankton. This could cause phytoplankton productivity decrease and zooplankton structure alteration. On the other hand, according to some estimations, apart from suspended particles, about 5 to 15 tones of phosphorus could come daily into the water while nodule extraction, which may facilitate the Gulf water eutrophication. Besides the sediment excavation and dumping should most probably lead to death of benthic organisms.
The field studies took place in June and December 2005 and in August and October 2006. Zoobenthos, phytoplankton and zooplankton were sampled at the nodule field and at the adjacent sea area. Besides the case study was performed aimed to reveal the short-term effects of environment condition changes inside the high turbidity spot (formed during the nodule extraction) on the state of pelagic biological communities.
The species composition as well as density and biomass of both phyto- and zooplankton inside the nodule field did not differ much from that in the adjacent sea area. The dominating species was typical for the eastern part of the Gulf of Finland. The blue-green algae prevailed in phytoplankton while copepods played significant role in zooplankton.
The species composition of benthic invertebrates in the area investigated was also typical for the eastern part of the Gulf of Finland. Oligochaeta, Polychaeta and Amphipoda were among the commonest benthic invertebrates. Unlike the pelagic communities the benthic community at the nodule field differed strongly from that outside the field. At the nodule field the species diversity and abundance of benthic invertebrates were several times lower than in the adjacent sea area over the whole period of investigations. Isopoda, usually prevailed in this part of the Sea, were not reported from the nodule field. The amount of Oligochaeta, Polychaeta, Mollusca and Chiromomidae decreased dramatically as well.
In high-turbidity spot both phyto- and zooplankton structure did not differ much from that in the adjacent sea area. As well as in the other parts of the investigated area, the blue-green and green algae prevailed in phytoplankton. Meanwhile during the dredge activity some benthic forms of diatom algae have appeared in small amount in upper water layer. During the next few hours after the nodule extraction has been stopped they disappeared from the phytoplankton, which was caused by unfavorable (for them) temperature and salinity conditions. At the same time the biomass dynamics of dominant species was not unidirectional. In zooplankton in the area of high turbidity the increased amount of dead Cladocera was observed (Filippov et al., 2006).
In the coastal zone of the Kiperort Island close to the nodule field the structure of both benthic and pelagic associations was typical for the coastal zone of this part of the Finnish Gulf. At the stations nearest the nodule field the amount of phytoplankton invariably exceeded that at the remote stations. Meanwhile both the zooplankton and zoobenthos structure were similar throughout the investigated coastal area.
Overall our investigations have revealed that transformation of environment caused by the process of nodule extraction lead to short-term changes in phytoplankton structure and to increased mortality in some zooplankton groups. Some increase in phytoplankton biomass was observed in the coastal zone, nearest to the nodule field. In long term, the sediment excavation and dumping strongly affected benthic organisms at the nodule field. Many-fold decrease in both benthic invertebrate abundance and diversity was observed in the dredging area.
