Water quality of the Waiohewa Stream, Rotorua

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Abstract
The chemical quality of the Waiohewa Stream, Rotorua, was assessed from the results of 2 longitudinal surveys in summer, 1978-1979. Changes in N concentration were examined. The quantity of ammonia increased downstream from unmonitored geothermal inputs but, after dilution and neutralization by a larger inflow of freshwater, considerable proportions of ammonia were converted to nitrate. In the 1st survey ammonia concentrations decreased from 4.48 to 2.47 g/m3 and nitrate concentrations increased from 0.59 to 1.13/g3 in a 3 km stretch of the stream. Mass flow calculations showed that nitrification could have accounted 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 B (1.1-4.0 g/m3), filterable Hg (0.1-0.8 mg/m3) and As (10-14 mg/m3).