Chemical runoff from pasture: The influence of (Fertiliser and riparian zones

Abstract

Runoff of phosphorus, nitrate, ammonium, calcium, magnesium, sodium, potassium, chloride, and sulphate was measured in 15 storms and at low flows in 3 “nested” experimental catchments converted from scrub to pasture. Multiple regression analysis suggested that over 2#fr1/2> y, fertiliser application had a cumulative effect on the concentrations of calcium, potassium, and sulphate in storm waters leaving the experimental basin, but only in the flood waters from the small wholly‐grassed sub‐catchment (Pukeiti) was there an increase in phosphorus concentrations. A similar pattern was observed at baseflows. Reactive phosphorus losses of up to 1 kg.ha^?1 left Pukeiti in post‐fertiliser storm events but mean losses from the whole basin were only about 0.004 kg.ha^?1 per storm and there was little evidence of any fertiliser effect. The stream below Pukeiti has well developed riparian vegetation with marsh and scrub.

The phosphorus losses from the basin seem of little significance agriculturally and environmentally. Although the losses from Pukeiti sub‐catchment were of siufficient magnitude to have a strong impact on water quality in waterways and lakes (mean total phosphorus concentration in post‐fertiliser floods 1.91 g.m^?3) this sub‐catchment appeared to have little effect on the quality of water eventually leaving the whole basin.

The results are discussed in relation to sub‐catchment differences and it is suggested that they give support to the use of riparian zones along streams to reduce phosphorus runoff.