Seabed responses to wood waste in Northumberland Channel
Date
1987
Authors
Ostrovsky, Irina
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Abstract
A study of Northumberland Channel situated between Vancouver and Gabriola Islands in British Columbia, Canada, was undertaken to assess the status of benthic communities present and to relate their condition to chemical-physical sedimentary processes occurring under continuous deposition of wood waste material from a pulp mill underwater outfall.
A mid- channel transect of stations located at distances increasing in a geometrical progression elucidated an organic enrichment gradient, which was marked by decreasing levels of undegraded woody byproducts (mainly fly ash). The presence of fly ash, in three stations closest to the diffuser, as a densely packed layer buried under 5 to 10 cm of recent sediments indicated average sedimentation rates (1.25- 2.25 cm/ year) in the channel. Large variability of environmental parameters, greatest in stations closest to the outfall, suggests a non-homogeneous environment.
A benthic community exhibiting a variety of transitional stages and dominated by three small deposit feeding Polychaete families (Capitellidae, Cossuridae, Cirratulidae) was desc ribed. An ordination analysis (DCA) on Polychaete data from a 0.5 mm screen separation produced a first axis significantly correlated with percentage of coarse wood (by volume) in grab samples.
A failure of cluster analysis to separate distinct station clusters and high similarity levels indicate a data continuum with high within station variability. It is proposed that such variability is partially based on the patchy deposition of woody compounds whose degradation forms the basis of a sulfuretum in Northumberland Channel.
The presence of a Beggiatoa mat on the sediment-water interface at station Tl, in front of the diffuser, was associated with the highest sulfide levels in the sediment pore water and well oxygenated water column, as well as the high levels of cellulose in the surface sediments. A corresponding decrease in abundance and number of taxa of nonmotile macrobenthos in this station is attributed to increased sulfide levels. No accumulation of pulp fiber in the sediments was observed. High rates of cellulose degradation encountered in the first few centimeters of sediment are in accord with the Vance model.
It is therefore concluded that due to well-flushed oceanographic conditions in the channel and the tendency of pulp mill effluent to flocculate in sea water, sediments of Northumberland Channel receive highly variable amounts of mill-derived organic loading. Such loadings lead to the development of variable levels of sulfide accumulation and corresponding anoxia, which is reflected in elimination of highly sensitive species and proliferation of fast breeding opportunists, characteristic of transitional stages of impacted communities.