I'r - Memorial University of Newfoundland

5.1.4 and Section 4.1.2). This cluster is observed in all three basins and can generally be
explained in tcnns ofsurface and bottom circulation patterns.
The incorporation ofsites located in the Central Basin into Cluster 3 can be
expl ained by the absence ofmajor fluvial input along the shore andspecific circulation
pattern in this part of the lake. Most ofthe stations within the cluster are found in the
northern part ofthe lake. There arc no major rivers or cities along this shore which could
introduce signi ficant pollution signal. A study at Wheatley Harbor showed that minor
tri butaries are unlikely to significantly contribute to the PAH pollution ofthe offshore
sediments (Appendix C3) . The surface flow in the Central Basin is directed away from
the northe rn shore (Fig. 5. 1.10), while compensatory bottom currents intensive at the
sou thern shore slow down and drop most ofthe suspended load by the time they reach the
north ern locat ions (Fig. 5.l.8). Furthermore. the lon gshore currents are directed in such a
way that no pollution penetrates this part ofthe lake from the Western Basin (Fig. 5. 1.7).
The trace level PAH pollution observed within this cluster (Fig. 4.1.1, 4.1043, 5. 1.3) can
poss ibly be considered as some background characteristic of the lake sediments.
The inclusion of the two stations from the Western Basin into this cluster possibly
has a different explanation. The isclared position ofstation 967 (Fig. 5. 1.1) can again be
explaine d in term s of surface circulation. Before entering the Pelee Passage the flow of
the Detroit River splits into two arms due 10the complicated bottom topography (Fig .
5.1.11) The northern branch passes closer to the shore while the southern part is
deflect ed towards Pelee Island (Fig. 5.1.12). Thi s pattern leaves site 967 relatively
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