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

 

Situation: High nutrient loads from agricultural runoff can degrade water quality and ecosystem health. Drainage systems in agricultural landscapes can rapidly transport large quantities of dissolved nutrients to surrounding streams, bypassing the natural attenuation processes of shallow groundwater and riparian zones. Using constructed wetlands to intercept agricultural drainage can help to improve water quality. 

 

Actions: A study conducted by the National Institute of Water and Atmospheric Research in Hamilton, New Zealand evaluated the ability of constructed wetlands to remove nitrogen (N) and phosphorus (P) from three intensively grazed dairy pasture sites over a 3 to 5 year period. 

 

Take-home message: 

• All three wetlands removed significant amounts of N.
• None of the wetlands effectively removed P.
• N removal was limited during colder months.
• Controlling the rate of flow from the tile drains into the wetlands to extend the contact time during high-flow events would increase the effectiveness of wetlands.

 

For more information:

• Tanner, C.C. and J.P.S. Sukias. 2011. Multiyear nutrient removal performance of three constructed wetlands intercepting tile drain flows from grazed pastures. Journal of Environmental Quality 40:620-633.
• Email Chris C. Tanner c.tanner@niwa.co.nz