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Would the ocean be any better?
If the city’s wastewater discharge is no longer acceptable in
the Estuary, why should it be acceptable in the ocean? The Estuary is acknowledged as having international
significance as a wetland, and although the present discharge
removes 99.9 per cent of pathogens, the nutrients within the
discharge have a significant effect on the ecology of the
Estuary. Because the Estuary is a shallow, relatively enclosed body
of water, it supports a wide range of flora and fauna which
is affected in different ways due to the low dilution the
Estuary provides for these nutrients. Removal of the
nutrients, it is believed, will reduce sea lettuce growth by a
minimum of 50%, and reduce anoxic areas where sea lettuce
accumulates. Juvenile fish have also been identified as likely to benefit
from removal of exposure to the low levels of ammonia in
the discharge. The colour and clarity of water within the
Estuary will also improve by removal of the discharge which
contains green algae. From an ocean outfall the dilution achieved by the time the
discharge reaches the surface would be approximately 100
times, making the effect of nutrients and any remaining
pathogens minor. The modeling conducted on an ocean outfall to date
indicates that on the infrequent occasions the discharge
would go directly to the New Brighton beach (under certain
conditions, over a period of about four tides) it will be safe
to gather shellfish at the foreshore. In fact the model
suggests that an ocean outfall will have significantly less
impact on shellfish on the beaches than an Estuary outfall. |