RELATIONSHIP OF FORAMINIFERA AND THECAMOEBIAN DISTRIBUTIONS TO SEDIMENTS CONTAMINATED BY PULP-MILL EFFLUENT - SAGUENAY FJORD, QUEBEC, CANADA

Gravity cores and grab samples collected in the Saguenay Fiord between 1976 and 1988 contain the record of a 20th century benthic marine environment contaminated primarily by organic matter discharges from several local pulp and paper mills. Spiroplectammina biformis is the dominant arenaceous species. Its living percent abundance decreases between 1982 and 1988 as a consequence of the apparent recolonization of the upper reaches of the fiord by several arenaceous taxa, the most important being Textularia earlandi. Cassidulina reniforme, the dominant living calcareous species, shows about a three fold increase in relative abundance over the six year interval. Grab sample observations also suggest a recolonization of some formerly barren benthic environments near the head of the fiord by foraminiferal species between 1982 and 1988. This recolonization may reflect the combined effect of government regulations imposed on local industrial polluters in the early 1970's and the capping of a large area of contaminated sediment by a layer of clay that was transported to the basin at the head of the fiord as the result of a catastrophic landslide in 1971. X-radiographs of core sections from a basin at the head of the fiord show sharp laminations that reflect both the absence of bioturbators and the seasonal variation of fluvial depositional processes. Organic waste deposition from pulp and paper mill outfalls first increased around 1910 and shows a first order inverse relationship to benthonic foraminiferal assemblage diversity. The presence of only allochthonous thecamoebian and reworked planktonic Foraminifera tests in many benthonic Foraminifera-barren core intervals supports the idea that common indigenous estuarine species such as Spiroplectammina biformis were excluded from these areas at certain times as a consequence of pollution "stress" rather than having been removed from the sediment record as a result of post-depositional diagenetic effects. However, future studies of estuarine pollution history based on proxy foraminiferal data from cores must give greater emphasis to distinguishing ecological stress responses from diagenetic process (i.e. test dissolution effects) since both mechanisms can be reflected in the proxy pollution "signal" in a similar way.