The Effects of Soil Moisture and Emergent Herbaceous Vegetation on Carbon Emissions from Constructed Wetlands

Abstract

Wetlands serve as sinks for carbon and nutrients but they are also a large source of greenhouse gases. Our objective was to quantify emissions of carbon dioxide (CO2) and methane (CH4) from three free water surface-flow constructed wetlands in the presence and absence of emergent herbaceous vegetation (Typha angustifolia L. and Typha latifolia L.) across a gradient of soil moisture. Measurements were collected on eight sampling dates during June and July, 2014. Similar to previous research, CO2 emissions were higher in vegetated plots, increasing from a median ± std. error of 242 ± 29 to 1612 ± 95 mg m−2 h−1. Emissions of CH4 were also significantly higher in vegetated plots, but the relative magnitude of the effect of plants varied among wetlands. Emissions of CH4 were highest from vegetated plots in the wetland with the highest soil moisture (4.4 ± 1.0 mg m−2 h−1). However, the largest effect of plants on methane emissions occurred in the wetland with intermediate soil moisture, with a 15-fold increase in CH4 emissions from 0.15 ± 0.90 to 2.4 ± 1.2 mg m−2 h−1. Design and management that consider the interactive effects of soil moisture and plants on CH4 emissions may help reduce the greenhouse gas footprint of constructed wetlands.