New Zealand Journal of Marine and Freshwater Research abstracts

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Residence times of Manukau Harbour, New Zealand

W.N.VANT B. L. WILLIAMS

Water Quality Centre National Institute of Water and
Atmospheric Research Ltd P.O. Box 11-115 Hamilton, New Zealand

Abstract Residence times of the three main channel systems of Manukau Harbour were calculated by methods based on the salinity measured in 10 tidal excursion segments: the freshwater replacement technique and a volume exchange model. The amount of freshwater present in the segments at high water was low (< 11% throughout the year), so salinities were high, with minimum values (winter) in each segment being in the range 30.1-34.0 (compared with a median value of 34.5 in the nearby coastal waters). The proportion of each segments' volume which was exchanged with an adjacent segment during a tidal cycle varied markedly across the harbour, from < 5 % in several shallow inner harbour segments to 65% in a deep segment adjacent to the entrance channel. For annual average conditions the freshwater replacement times of the channels were 11-18 days. Slightly longer residence times - 12-26 days - were obtained from the volume exchange model. Calculated replacement times for two non-conservative tracers - inorganic phosphorus and nitrogen - were approximately half those for freshwater, as 5-12% of these species disappeared from the water column each day.

Keywords residence time; flushing; salinity; freshwater replacement; volume exchange; phytoplankton; Manukau Harbour M92022 Received 28 April 1992; accepted 28 September 1992

New Zealand Journal of Marine and Freshwater Research, 1992, Vol. 26:The Royal Society of New Zealand 1992
Received 28 April 1992; accepted 28 September 1992 Vol. 26:393-404 The Royal Society of New Zealand 1992

PDF file of entire paper: medium quality (947K); (scanned from paper original: notes about this process)

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