Multiyear nutrient removal performance of three constructed wetlands intercepting tile drain flows from grazed pastures.

摘要: Subsurface tile drain flows can be a major s ource of nurient loss from agricultural landscapes. This study quantifies and nitrogen phosphorus yields drains at three intensively grazed dairy pasture sites over 3- to 5-yr periods evaluates the capacity constructed wetlands occupying 0.66 1.6% drained catchments too reduce nutrient loads. Continuous flow records are combined with automated flow-proportional sampling concentrations calculate wetland mass removal rates. Annual drainage water rangedfrom 193 564 mm (16-51% rainfall) two rain-fed 827 853 (43-51% rainfall + irrigation) an irrigated site. Annually, exported 14 109 kg ha(-1) total N (TN), which 58 90% was nitrate-N. Constructed intercepting these removed 30 369 gTN m(-2) (7-63%) influent loadings annually. Seasonal percentage nitrate-N TN were negatively associated loadings. Wetland P poor in all wetlands, 12 115% more annually overall than received. 0.12 1.38 ha P, 15 93% dissolved reactive P. Additional measures required losses or provide supplementary removal. performance could improved by modifying systems release gradually improving irrigation practices losses.