Using constructed wetlands to treat subsurface drainage from intensively grazed dairy pastures in New Zealand.
Performance data, during the start-up period, are presented for constructed wetlands treating subsurface drainage from dairy pastures in Waikato (rain-fed) and Northland (irrigated), North Island, New Zealand. The wetlands comprised an estimated 1 and 2% of the drained catchment areas, respectively. Nitrate concentrations were high in the drainage inflows at both sites (medians 10 g m(-3) at Waikato and 6.5 g m(-3) at Northland), but organic N was also an important form of N at Waikato (37% of TN). Comparison of wetland inflow and outflow nutrient concentrations showed overall nutrient reductions during passage through the wetlands for NO3-N (34 and 94% for medians, respectively), TN (56 and 33%, respectively), and DRP (80%, Northland only). Median NH4-N (both sites) and DRP (Waikato) concentrations showed apparent increases between the wetland inlets and outlets. However, a mass balance calculated for the 3 month preliminary monitoring periods showed substantial mass removal of DRP (80%) and all measured forms of N (NO3-N 78%, NH4-N 41%, Org-N 99.8% and TN 96%) in the Waikato wetland. Monitoring of these systems needs to be continued through a range of seasons and years to fully assess their long-term performance.
Tanner
C C
CC
National Institute of Water and Atmospheric Research, PO Box 11-115, Hamilton, New Zealand. c.tanner@niwa.cri.nz
Nguyen
M Long
ML
Sukias
J P S
JP
D000818:Animals; D001673:Biodegradation, Environmental; D002417:Cattle; D003612:Dairying; D017753:Ecosystem; D005160:Facility Design and Construction; D005374:Filtration; D009520:New Zealand; D009584:Nitrogen / Q000302:isolation & purification*; D014865:Waste Disposal, Fluid / Q000379:methods*; D018508:Water Purification / Q000379:methods*
D009584:Nitrogen