New Zealand Journal of Marine and Freshwater Research abstracts

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Water quality of the Waiohewa Stream, Rotorua

R. B. WILLIAMSON

J. G. COOKE

Water and Soil Science Centre Ministry of Works and Development Private Bag Hamilton, New Zealand

Abstract The chemical quality of the Waiohewa stream, Rotorua, was assessed from the results of 2 longitudinal surveys in summer 1978-79. In particular, changes in nitrogen concentration were examined. The quantity of ammonia increased downstream from unmonitored geothermal inputs, but, after dilution and neutralisation by a larger inflow of freshwater, considerable proportions of ammonia were converted to nitrate. In the first survey ammonia concentrations decreased from 4.48 to 2.47 g m~³ and nitrate concentrations increased from 0.59 to 1.13 g "³ in a 3-km stretch of the stream. Mass flow calculations show that nitrification could account for at least 55% of the ammonia decrease, the rest probably being lost through assimilation or denitrification. Laboratory incubation experiments showed that nitrification occurred in the stream bed. The geothermal waters contained low concentrations of boron (l.l^t.O g m"³), filterable mercury (0.1-0.8 mg m~³) and arsenic (10-14 mg m"³).

Keywords Waiohewa Stream; Rotorua; water quality; geothermal; nitrogen; nutrients; toxicants; oxygen demand; water analysis; water sampling; nitrogen cycle

New Zealand Journal of Marine and Freshwater Research, 1982, Vol. 16 : 327-337
Received 24 February 1982; accepted 27 May 1982

PDF file of entire paper: medium quality (703K); (scanned from paper original: notes about this process)

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