Metabolism and methane flux of dominant macrophyte communities in created riverine wetlands using open system flow through chambers

Estimating net primary productivity of macrophytes is a common practice in wetland research, but much less is done regarding gross primary productivity (GPP) and respiration (R) of wetland macrophyte communities. The purpose of this project was to estimate metabolism (GPP and R) and greenhouse gas emissions (methane) of wetland macrophyte communities using an open system flow-through chamber to determine the gaseous carbon budget. Large (0.5 m2, 1.6 and 2.6 m tall) flow-through chambers were placed over dominant macrophytes communities (2010: Typha spp., Scirpus fluviatilis, Sparganium eurycarpum, and Phragmites australis; 2011: Typha spp., S. fluviatilis, P. australis, and open water) in two wetlands in central Ohio, USA. Gas samples were collected over a 48-h period monthly from April through September. Samples were collected using a vial and syringe method from the chambers every odd hour between sunrise and sunset to estimate photosynthesis, and twice nightly to estimate respiration. Overall metabolism measurements were similar in the two years: 2010, GPP = 13.9 ± 1.2 g CO2-C m−2 day−1; R = 12.1 ± 1.0 g CO2-C m−2 day−1; 2011, GPP = 13.9 ± 1.1 g CO2-C m−2 day−1; R = 12.9 ± 0.6 g CO2-C m−2 day−1. GPP peaked in June 2010 and in July 2011 and overall was approximately 3.7% of solar radiation. GPP differed by both month sampled and plant community (p < 0.001 and p = 0.002, respectively). P. australis and Typha spp. had higher average GPP than did open water and P. australis had higher GPP than S. fluviatilis. Median methane emissions from the sample plots were 12.8 mg CH4-C m−2 h−1 and differed by month (p < 0.001) and soil temperature (p = 0.049). Based on this study, net retention of carbon in the two experimental wetlands ranged from 160 to 195 g C m−2 yr−1; these values compared well with other published estimates for the same wetlands.