The impact of stormwater discharges on freshwater, marine water and marine sediments and the implications for environmental management of the Pauatahanui Inlet, Porirua, New Zealand: A thesis prepared in partial fulfilment of Masters of Applied Science (Natural Resource Management), Massey University.
A survey of Cu, Pb, Zn and Cr levels in sediment cores taken at
four locations in the
Pauatahanui Inlet has been undertaken in conjunction with a
freshwater and marine
water quality survey.
Levels of heavy metals in sediment were within the Australian
and New Zealand
Guidelines for Fresh and Marine Water Quality for the protection
Ecosystems, [Interim Sediment Quality Guideline (ISQG) (high
level of protection)].
Sediments in the vicinity of discharges from suburban catchments
levels of Cu, Pb, Zn and Cr than those in the vicinity of rural
Levels of Cu, Pb and Zn in streams in the suburban catchments
levels for 99% species protection on occasions, and guidelines
for Cu, Pb and Cd
were exceeded in marine water. Elevated concentrations of heavy
metals in marine
and freshwater coincided with rainfall events and increased
levels, indicating stormwater discharges as a contributing
source of the contaminants.
Levels of N and P exceeded guideline trigger values in
freshwater tributaries on
occasions. There was no distinct difference between the rural
catchments in terms of nutrient levels detected.
Levels of bacteria present (E-Coli and Enterococci) exceeded NZ
guideline levels for
contact recreation purposes after rainfall events.
Heavy metals in stormwater were attributed to transport sources.
Control of these
discharges will likely be ‘end of pipe’ in nature due to the
diffuse nature of the heavy
metal inputs, and the difficulties in controlling emissions from
vehicles at source.