Methane And Carbon Dioxide Emissions From Different Types Of Riverine Wetlands

Wetlands are important ecosystems involved in global carbon cycle. Wetlands are both producers and consumers of the greenhouse gases. Controlling methane (CH4) and carbon dioxide (CO2) emissions from temperate zone wetlands created and restored for habitat replacement and water quality improvement is important. The objective of our study is to estimate and compare temporal and spatial patterns of methane emissions from wetlands and riparian ecosystems with different vegetations types and hydroperiods; to filter out the environmental parameters controlling net CH4 and CO2 emissions. For the study took place in the same area, it is better for the quantitative study of CH4 and CO2 emissions.In the research conducted for this dissertation, investigations were carried out in riparian wetlands at the Wilma H. Schiermeier Olentangy River Wetland Research Park (ORWRP) in Columbus, Ohio, USA. The 20 ha ORWRP includes several wetlands that are differing in vegetation type and water conditions, which are human-planted experimental freshwater marshes (wetland 1), naturally colonized experimental freshwater marshes (wetland 2), a river diversion oxbow (oxbow) and a riverside bottomland (riverside). A non-steady-state chamber design was used for gas sampling, with permanent chamber bases located in dry and shallow water zones, and a portable floating chamber deployed in deeper, permanently inundated zones. Sampling locations were chosen according to hydrology and different types of wetlands. Gas fluxes were measured from November 2008 to October 2009. Plots were distributed along longitudinal (from inflow to outflow) and transverse (from shallow transition edges to deepwater open water zones).At ORWRP, CH4 and CO2 emissions varied remarkably in both temporal and spatial terms. The range of median value methane emissions:riverside (0.33-85.7 mg-CH4-C m-2 h-1)＞wetland 1 and wetland 2 (0.02-20.5 mg CH4-C m-2 h-1)＞oxbow (-0.04-0.09 mg CH4-C m 2 h-1); The median (average) values of CO2 emission rates for wetland 1, wetland 2, oxbow and riverside were 9.8(19.2),13.5(20.6),24.7(36.0) and 33.7(40.3) mg CO2-C m-2 h-1 respectively. Soil temperature had a significant relationship with CH4 emissions in wetland 1 (R2=0.88), wetland 2 (R2=0.86) and riverside (R2=0.85), while the relationship was not significant between CH4 emissions and soil temperature in oxbow siteSoil temperature had a significant relationship with CO2 emissions in wetland 1(R2=0.63), wetland 2 (R2=0.54) and oxbow (R2=0.67) as well. There was a negative relationship between CO2 emissions and soil water content in different types of wetlands (R2=0.72). Nature wetlands have the higher CH4 and CO2 emission rates than created wetlands in river riparian zone here. Overall, our results showed that the edge of a river in a bottomland hardwood forest had the much higher CH4 and CO2 emissions than did created river diversion marshes. The spatial variation of the different types of riverine wetlands is caused by a combination of flood frequency, sediment organic carbon content, groundwater fluxes, and wetland productivity.Methane fluxes from the created oxbow were extremely low, with no more than 0.09 mg CH4-C m-2hr-1. The oxbow had distinct wet and dry seasons led to the low CH4 emissions. Another reason for the low CH4 production at the oxbow may be related to its low soil C content and the lacks of emergent vegetation. There was a seasonal pattern of CO2 emissions. The CH4 emission rates of open water zone and transition zone of oxbow were not different (p=0.593), were 0.03 (0.06) and 0.03 (0.12) mg m-2 hr-1. The CO2 emission effluxes was significantly lower in open water zone (15.5(20.9) mg CO2-C m-2 h-1) than in transition zone (38.7(63.0) mg CO2-C m-2 h-1). For the two created wetlands, there were significantly high rates of CH4 and CO2 emissions from deep water zones compared to transition zones during steady-flow conditions (p=0.000).Thus, hudrologic dynamics must be carefully planned in created and restored wetlands. It would be worth replicating this wetland design with in its long and shallow shape and wet-dry-wet pulsing conditions throughout the world's river floodplains.When the two experimental wetlands were compared, the natural-colonizing wetland has more methane emissions than human-planted wetland (p=0.047), which were 114 g CH4-C m-2 y-1 and 68 g CH4-C m-2 y-1. The reason may be due to its history higher net primary productivity and the higher biodiversity of wetland 1. We also found that from 2004 to 2009, mean annual methane emissions for wetland 1 increased from 16 g CH4-C m -2 y-1to 68 g CH4-C m-2 y-1, and for wetland 2, from 31 g CH4-C m-2 y-1to 114 g CH4-C m-2 y-1, maybe for the cumulative productivity and higher carbon content in soil. Comparison among the nature-planted and human-planted wetlands suggested that methane emissions from created freshwater riverine wetlands greatly depend on the NPP and hydrology. Riparian created wetlands can be designed to emit less CH4 and CO2 gas possibly by providing the proper vegetation development.