Tuesday, November 14, 2006 - 9:15 AM

Greenhouse Gas Emissions fom Agricultural Treatment Constructed Wetlands: Growing Season vs. Non-Growing Season.

V.M. Glass1, R.J. Gordon1, and C. Wagner-Riddle2. (1) Nova Scotia Agricultural College, P.O. Box 550, Truro, NS B2N 5E3, Canada, (2) Univ of Guelph, Dept of Land Resource Sciece, Richards Building, Guelph, ON N1G 2W1, Canada

In Nova Scotia, a shift has occurred focusing on constructed wetland systems as an effective treatment option for agricultural wastewater.  Although much research has examined the water quality treatment aspects of these systems, there has been limited interest in examining the air quality effects.  As such, the objectives of this study were to examine the changes between growing season (GS) and non-growing season (NGS) greenhouse gas emissions from these living treatment systems.  Six pilot-scale (6.6 m2) constructed treatment wetlands were established at the Nova Scotia Agricultural College's Bio-Environmental Engineering Centre in Truro, Nova Scotia, Canada.  The wetlands were constructed to allow for continuous wastewater loading at two rates: typical (70 L d-1) and high (140 L d-1) and contained either aquatic vegetation (cattails) or no vegetation.  Each wetland had a removable chamber to allow for continuous measurements of CO2, CH4, and N2O emissions using a mass balance approach.  During the GS, average CO2 uptakes were large (approximately -40 g CO2 m-2 d-1) for the wetlands with dense vegetation (approximately 100% cover) at the typical loading rate.  For those wetlands at higher loading rates, CO2 emissions were observed to be as high as +11 g CO2 m-2 d-1.  Methane emissions from the wetlands were closely related to the presence of plants and wastewater strength.  Wetlands with typical wastewater loading rates and an abundance of aquatic vegetation produced average CH4 fluxes of approximately 35 mg m-2 d-1, while higher wastewater strength systems with little vegetation approached 85 mg m-2 d-1.  During the NGS, all vegetated wetlands exhibited higher CH4 emissions than the non vegetated systems.  Nitrous oxide emissions were generally negligible for all the wetlands, regardless of time of year.