INTERACTIONS BETWEEN EUTROPHICATION AND CONTAMINANTS .1. PRINCIPLES, EXPERIMENTAL-DESIGN AND SYNTHESIS

In marine environments influenced by human activities, the sea-bed is a major recipient of both contaminants and organic matter. Deposition and recycling of contaminants from bottom sediments may be affected by the eutrophication status of the area. Contaminants and eutrophicatio n factors may alsb interact to affect bioaccumulation as well as the g rowth, health and reproduction of benthic organisms. Consequently, fro m an environmental management point of view, these interactions should be considered when decisions are made about input of contaminants and organic matter to the aquatic environment. In order to elucidate inte raction patterns between eutrophication and contaminants, radio-labell ed contaminants were applied in a large scale experiment performed at Marine Research Station Solbergstrand, situated by the Oslofjord, Norw ay. The continous flow through experiment was performed in glass aquar ia containing three sediment-dwelling species (Abra alba, Nereis diver sicolor and Amphiura filiformis) placed in marine clay sediments. Blue mussels (Mytilus edulis) were kept in separate downstream aquaria and exposed to the outflowing water from the sediment aquaria. In 12 cont aminated aquaria the sediment was spiked with Hg-203 (0.23 mg Hg kg(-1 ) dry sediment), Cd-109 (5 mg Cd kg(-1)) and C-14-benzo[a]pyrene (1 mg BaP kg(-1)). In 12 organically enriched aquaria, phytoplankton (2 mg C kg(-1) dry sediment) was initially mixed into the sediment and two m onths later another batch corresponding to 20 g C m(-2) was added to t he aquaria. Finally, the concentration of oxygen was continuously lowe red from 7-9 mg O-2 l(-1) in 12 well-oxygenated aquaria to 2.4-3.5 mg O-2 l(-1) in 12 low-oxic aquaria by purging the source water with nitr ogen. Allowing three replicate aquaria for each treatment, all combina tions of the two levels (high/low) of the three factors (contaminants, oxygen availability and carbon load) could be tested in a factorial d esign using 24 aquaria. Sulphide ion activies were continuously record ed by Ag/AgS electrodes in the sediments and overlying water, and redo x potentials were measured by Pt-electrodes inserted in the sediment. There were only minor changes in redox and sulphide potentials during the experimental period. Also, mortalities of the test species were ne gligible in all aquaria. After an experimental period of three months, the concentration of contaminants was quantified in sediments, porewa ter and biota using beta/gamma emission from the isotopes. Effects of the treatments on sediment-dwelling invertebrates were assessed using growth (Nereis, Abra and Amphiura), arm regeneration (Amphiura) and bi omarker responses. In this paper (paper I) the principles and hypothes es for studying interactions between organic loading and contaminants are outlined as well as the experimental design. The results from the experiment are presented in three separate papers (papers II-IV) elsew here in this volume. A short synthesis is presented in this paper, com paring the conclusions from the individual studies. (C) 1997 Elsevier Science Ltd.