Nitrogen and phosphorus in the Ngongotaha Stream

Abstract

This paper gives the data and methods used to calculate the nitrogen and phosphorus loads of the Ngongotaha Stream, near Rotorua, New Zealand. The variations in concentration with time and with flow rate are given in some detail, as examples of what may happen in other streams of the central volcanic plateau, and a novel way to define a flow-concentration curve is described. Nitrate, ammonia, dissolved reactive phosphorus (DRP), total phosphorus (TP), and total Kjeldahl nitrogen (TKN) concentrations were measured, and mean concentrations in 1976 base flow were found to be 527, 25, 32, 48, and! 162 mg m -3 respectively. Nitrate concentrations showed seasonal variations, and although changes occurred during floods, they were not correlated with flow rate. DRP concentrations showed little variation, except that they dropped at the peak of the largest floods. TP was strongly correlated with flow rate during floods, and TP loads could best be calculated by allowing for a curvilinear relationship between concentration and flow rate. The logarithms of the TP load carried by a flood and the peak flow rate of the flood were highly correlated

Trends in lake Rotorua water quality

“…Stream nutrient concentrations and mass flow rates were estimated by Fish (1975Fish ( ) in 1968Fish ( -1970 and again by Hoare (1980a) in 1976 has made a careful comparison of the results and concluded that, although slightly different analytical and sampling methods were employed, phosphorus and ammonia concentrations had not changed significantly. Fish's mean nitrate concentrations were, however, 25-50% lower than Hoare's values and Fish reported an increase with time in some streams (Fish & Andrew 1971).…”

“…I assumed that stream nutrient concentrations did not change, during the course of the study, from the average values measured by Hoare in 1976Hoare in -1977 For streams known to drain through urban areas served by septic tanks, nitrate concentrations measured upstream from the housing areas were used to avoid including sewage nitrogen twice. Although a seasonal pattern was detected in nitrate concentrations (Hoare 1982), constant average values were used for all nutrient species.…”

“…Nutrient concentrations in rainfall measured by Fish (1977) were assumed constant over the study period and were multiplied by rainfall at Rotorua Airport (scaled by 1.2 to give the average over the lake (Hoare 1980b)) and lake area, to give total direct nutrient input.…”

Hypolimnetic oxygen consumption in Lake Taupo, New Zealand: A preliminary assessment

“…Hoare (1982) found for the Ngongotaha River, which is the main inflow to Lake Rotorua, that flood conditions in 1976 provided 42% of the total P, almost all of which was in paniculate form (plus dissolved organic) in 3 days. 25% was supplied during only 16 h of the year.…”

Water chemistry dynamics as affected by rainstorms in a high‐elevation stream, South Island, New Zealand

“…In addition, recent concerns about nutrient enrichment and eutrophication of surface waters have resulted in considerable effort being directed toward studies in which N and P have been the primary focus (Hoare 1982;Smith 1987;Cooper & Thomsen 1988). Significantly, a large-scale systematic survey of water chemistry in New Zealand rivers was recently reported and provided an extensive data set defining baseflow water quality conditions.…”