New Zealand Journal of Marine and Freshwater Research abstracts

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Changes in water quality in Lake Horowhenua following sewage diversion

W. N. VANT

Water Quality Centre
DSIR Marine and Freshwater
Department of Scientific and Industrial Research
P. O. Box 11-115, Hamilton, New Zealand

B. W. GILLILAND

Manawatu Wanganui Regional Council Private Bag, Palmerston North, New Zealand

Abstract Sewage effluent was diverted away from Lake Horowhenua in 1987, and external loads of nitrogen and phosphorus are estimated to have since dropped by about 20% and 90%, respectively. Lakewater quality was monitored sporadically before 1984, and routinely since then. In the first 3 years since diversion, water quality in the winter has not improved (levels of TP, TN, chlorophyll a, and Secchi depth unchanged), although DRP levels are now low. Summer chlorophyll a level has halved, and it covaries significantly with TN level which has also fallen substantially. Summer TP and DRP levels have also more than halved, but remain very high (mean TP 420 mg m~³), primarily because of a large internal P load. Water clarity is still poor because levels of inorganic suspensoids and detritus have remained high.

Keywords eutrophication; chlorophyll a; nutrients; clarity; Lake Horowhenua M90044 Received 28 August 1990; accepted 29 November 1990

New Zealand Journal of Marine and Freshwater Research, 1991, Vol. 25: 57-61 0028-8330/2501-0057 $2.50A) © Crown copyright 1991
Received 28 August 1990; accepted 29 November 1990

PDF file of entire paper: medium quality (308K); (scanned from paper original: notes about this process)

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