Abstract
The Jøssingfjord area, Norway has been used since 1960 for sea disposal of finely ground, inert tailings from a titanium mine. The discharged quantity was about 2 million tonnes · year −1 in the 1980s. The submarine outfall was in 1984 relocated from the shallow Jøssingfjord to a deep basin outside the fjord entrance. Results reported here are from yearly monitoring surveys in the period 1983–1988. The aim of the study was to examine the structure of the soft bottom communities, and describe effects of mine tailings disposal after relocation. The spreading of mine tailings has generally remained constant after 1984. The relocation resulted in increased accumulation within 2–3 km from the new outfall. The accumulated material decreases rapidly with distance, from several metres · year −1 in the outfall basin, to 4–5 cm · year −1 within 1 km from the outfall site, and is in the order of 1 mm · year −1 at distances > 2–3 km from the outfall. Changes in the benthic fauna at varying distances from the outfall were followed. Despite complicated bottom topography and large variations in depth and sediment types it has been possible to identify the biological impact of mine tailings. For example, one year after relocation a clear increase in numbers of the typical opportunistic species Heteromastus filiformis, Chaetozone setosa and Cossura longocirrata was found. In the following years a significant reduction in diversity was observed at sites most disturbed by sedimentation, while diversity at sites > 2–3 km from the outlet remained unaltered. Multivariate analysis of the faunal data (classification, MDS and DCA ordination) revealed clear site-group differences, and two site-groups were related to tailings content in the sediment. Multivariate methods combining fauna and environmental variables identified depth and sediment content of tailings and organic matter as the most important factors influencing the structure of the benthic communities in the area. A sedimentation of 4–5 cm of tailings · year −1 resulted in changes in fauna composition, while at rate of 1 mm · year −1 no impact was observed on the fauna. Recolonization on the old tailings deposits inside Jøssingfjord commenced within one year after cessation of discharge, and within 4 years all the main macrobenthic phyla were represented.
Published Version
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