Application 124771 - Ministry of Fisheries

MAY 2012 REPORT NO. 2134 | CAWTHRON INSTITUTE
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5.5. Water column properties
A snap-shot of water column properties at the reference farm and control sites using
replicate CTD casts showed that the water column was well mixed at some reference
farm and control sites, but that a weak thermo- and halo- cline (stratification of
temperature or salinity) was present between 5-10 m at several sites (Figure 10). The
greatest range in salinity and temperatures was observed in the top 5-10 m of the
water column.
The range in chl-a, measured as fluorescence, was similar between control and farm
sites throughout much of the water column (Figures 11 and 12). Chl-a concentrations
were centred on 0.1 µg/L throughout much of the water column, but were significantly
higher at reference farm sites than control sites between 4-11 m depth (Figure 12).
Water column turbidity (as Formazin Turbidity Units, FTU) was similar between farm
and control sites in the top 3 m of the water column (Figure 11), but between 3-5 m
farm sites were less turbid; and below 12 m, farm sites were more turbid. This could
be attributed to filtration of the upper water column by mussels, and release of pseudo
faeces toward the lower water column.
In general, the top 10 m of the water column had the greatest variability in salinity and
temperature, but no consistent patterns or differences were observed in chl-a.
Wider-scale and longer-term monitoring and validated models will be necessary to
provide a greater understanding of the contribution of aquaculture to water column
properties in the Coromandel region.