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This article in JEQ

  1. Vol. 40 No. 2, p. 620-633
     
    Received: Nov 28, 2011


    * Corresponding author(s): c.tanner@niwa.co.nz
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doi:10.2134/jeq2009.0470

Multiyear Nutrient Removal Performance of Three Constructed Wetlands Intercepting Tile Drain Flows from Grazed Pastures

  1. Chris C. Tanner * and
  2. James P. S. Sukias
  1. National Institute of Water & Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand. Assigned to Associate Editor Gary Feyereisen

Abstract

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

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Copyright © 2011. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyAmerican Society of Agronomy, Crop Science Society of America, and Soil Science Society of America