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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 -3in 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 cfuper 100 Received 23 March 1999; accepted 23 June 1999 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. M99015

Water quality monitoring in Toenepi Stream, New Zealand, started in 1995 in a study of dairy farming influences on lowland stream quality and has continued since then with brief interruptions. Surveys have provided information about changes in farm and soil management practices as they relate to environmental sustainability. Although average water quality in Toenepi Stream has changed little during 1995-2004, there have been some notable improvements. Water clarity measured by black disc has improved from 0.6m to 1.5m, and median ammonia-N and nitrate-N concentrations have declined by 70% and 57%, respectively. The frequency and magnitude of extreme concentrations have declined-most notably for nitrogen (N) forms, which also had decreased mean values. Specific yields for suspended solids (SS) and phosphorus (P) forms in 2002-04 were 47-67% of 1995-97 values, mainly because of lower water yields. Reduced specific yields for N forms in 2002-04 (34-37% of 1995-97 yields) were also attributable to lower mean concentrations in stream water. Faecal bacteria concentrations have not abated and are on average 2-3 times recommended guideline values for contact recreation. Fewer dairy farms and an increased proportion irrigating dairyshed effluent to land, rather than discharging it to the stream via twopond systems, were likely causes of improvement in water quality. Water quality targets were developed for Toenepi Stream to achieve contact recreation criteria for the Piako River (downstream) and for intrinsic habitat values for Toenepi Stream. A range of mitigation measures has been formulated to meet these targets, but substantial uptake of sustainable farming practices is needed to improve water quality in Toenepi Stream.

Lentic wetlands are usually regarded as the most important natural freshwater sources of methane (CH 4 ) and nitrous oxide (N 2 O) to the atmosphere, and very few studies have quantified the importance of lowland streams in trace gas emissions. In this study, we estimated fluxes of CH 4 and N 2 O in three macrophyte-rich, lowland agricultural streams in New Zealand, to place their trace gas emissions in context with other sources and investigate the value of minimising their emissions from agricultural land. All three streams were net sources of both gases, with emission of CH 4 ranging from <1 to 500 μmol m −2 h −1 and of N 2 O ranging from <1 to 100 μmol m −2 h −1 during mid-summer. For CH 4 , both turbulent diffusion across the surface and ebullition of sediment gas bubbles were important transport processes, with ebullition accounting for 20-60% of the emissions at different sites. The emissions were similar on a per area basis to other major global sources of CH 4 and N 2 O. Although small on a catchment scale compared to emissions from intensively grazed pastures, they were significant relative to low-intensity pastures and other agricultural land uses. Because hydraulic variables (viz. depth, velocity and slope) strongly influence turbulent diffusion, complete denitrification can best proceed to N 2 as the dominant end-product (rather than N 2 O) in riparian wetlands, rather than in open stream channels where N 2 O fluxes are sometimes very large.