IMPACT OF WASTE FROM TITANIUM MINING ON BENTHIC FAUNA

The Jossingfjord area, Norway has been used since 1960 for sea disposa l of finely ground, inert tailings from a titanium mine. The discharge d quantity was about 2 million tonnes.year-1 in the 1980s. The submari ne outfall was in 1984 relocated from the shallow Jossingfjord to a de ep basin outside the fjord entrance. Results reported here are from ye arly monitoring surveys in the period 1983-1988. The aim of the study was to examine the structure of the soft bottom communities, and descr ibe effects of mine tailings disposal after relocation. The spreading of mine tailings has generally remained constant after 1984. The reloc ation resulted in increased accumulation within 2-3 km from the new ou tfall. 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 distan ces > 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 bee n possible to identify the biological impact of mine tailings. For exa mple, one year after relocation a clear increase in numbers of the typ ical opportunistic species Heteromastus filiformis, Chaetozone setosa and Cossura longocirrata was found. In the following years a significa nt reduction in diversity was observed at sites most disturbed by sedi mentation, while diversity at sites > 2-3 km from the outlet remained unaltered. Multivariate analysis of the faunal data (classification, M DS and DCA ordination) revealed clear site-group differences, and two site-groups were related to tailings content in the sediment. Multivar iate methods combining fauna and environmental variables identified de pth and sediment content of tailings and organic matter as the most im portant factors influencing the structure of the benthic communities i n the area. A sedimentation of 4-5 cm of tailings.year-1 resulted in c hanges in fauna composition, while at rate of 1 mm.year-1 no impact wa s observed on the fauna. Recolonization on the old tailings deposits i nside Jossingfjord commenced within one year after cessation of discha rge, and within 4 years all the main macrobenthic phyla were represent ed.