Environmental Assessment
Volume E-3.9
Tailings Facility
Oceanography
Ambatovy Project
106
January 2006
Water Quality Monitoring
In order to quantify the changes in regional water quality, the sample strategy
currently underway to assess the baseline conditions of the study must continue
into the operational phase. Currently, the focus is on sampling the waters in and
around the reefs (reference sites), but once operations begin, water samples will
also be taken within the outfall area.
Table 3.9-2 presents a summary of the of proposed target water guidelines, based
on known impacts of the various constituents on marine life. Although the
Malagasy water quality guidelines were used as the basis of the table, where
international limits were more stringent, these were selected. The rationale being
that these guidelines were selected based on a sensitive organism known to occur
in the Toamasina region. The trophic levels indicated in Table 3.9-2 will be
useful in selecting suitable indicator organisms, which are sensitive enough to a
particular constituent and could be used in a biological monitoring programme.
Species which are frequently monitored in these programmes include algae,
mussels and territorial reef fish. Selected sites on Nosy Faho and Le Grand Recif
would be ideal long-term monitoring sites.
3.9.4
Marine Outfall Impact Assessment
3.9.4.1 Key Issue - Construction of the Effluent Disposal Pipeline
Issue 1: Specific Impacts on the Nearshore Environment
Impact 1 - : Increased Turbidity As A Result Of Construction
Construction will require the burying of the effluent disposal pipeline above the
high water mark as well as sinking the pipeline into the sediments below the low
water mark for a short distance. This will require earthworks using heavy
machinery along the sandy beach habitats, as well as the re-suspension of
underwater sediments using a water jet in order to sink the pipeline to the
required depth. This will lead to increased turbidity during the construction
phase. Increased turbidity may influence marine organisms by restricting light
penetration and by smothering of smaller sessile organisms when sediment
resettles. This will lead to a decrease in the availability of food organisms for
larger species targeted by local fishermen. The increase in turbidity may also
result in the movement of fish away from the construction area.
