Water quality of a lowland stream in a New Zealand dairy farming catchment

A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m ‐3 in winter, with the bulk comprising nitrate nitrogen (NO ‐ 3 ‐N). During summer NO ‐ 3 ‐N was near zero and TN mostly comprised organic nitrogen. Maximum concentrations of total phosphorus (TP) and dissolved reactive phosphorus (DRP) were 1.64 and 0.555 g m ‐3 , respectively, and peaks coincided with spring and autumn applications of phosphorus fertiliser. Ammoniacal nitrogen concentrations exceeded 1 g m ‐3 on several occasions and mean concentrations at the three sites were 0.165–0.272 g m ‐3 . Faecal coliform and enterococci bacteria concentrations were 64–26000 and 7–23000 cfu per 100 ml, respectively. Specific yields of TN and NO ‐ 3 ‐N (35.3 and 30.7 kg ha yr ‐1 , respectively) were much greater than any previously reported for New Zealand pasture catchments, whereas TP and DRP yields (1.16 and 0.54 kg ha yr ‐1 , respectively) were more in accord with other studies. Greater use of land treatment of liquid wastes will reduce stream inputs of faecal organisms, NH 4 ‐N and P.