Spatial variability of CO2 efflux in a drained cropped peatland south of Venice, Italy

A field experimental study has been performed in a drained cropped peatland located in the Zennare Basin (south of the Venice Lagoon, Italy), to measure land subsidence due to peat oxidation and to address the primary relationships between the hydrological regime, the soil mass loss (in form of CO2 efflux to the atmosphere), and the settlement rate. The latter, of the order of 0.01-0.02 m/a, has been proved to be related to soil CO2 efflux due to organic matter oxidation. A series of CO2 emission measurement campaigns has been performed between the years 2003 and 2005. The non-steady-state chamber method was employed to assess the efflux spatial variability and detect its relationship with the main hydrological parameters controlling the oxidation reaction, i.e., soil temperature, soil moisture, and organic matter content. The measurements, carried out in two sites located 1.5 km apart, point out a great variability of the CO2 emissions both in space and time. While the time-dependent behavior can be explained by the seasonal fluctuation of soil temperature, spatial variability shows a weak correlation with the variation of environmental variables. Statistical data analyses show that CO2 efflux can be considered lognormally distributed and that the process is stationary within each site but not in the whole basin, though the properties of the outcropping peat layer and the soil surface seem apparently uniform. A geostatistical analysis reveals two different spatial correlation structures, with scales of spatial dependence of approximate to 30 m and approximate to 180 m. Finally, the collected data show that invasive agricultural practices such as deep plowing, tilling, and harrowing, largely used in the Zennare Basin, induce significant disturbances that are not easily recognizable during the flux surveys and that casually affect the temporal and spatial variability of the oxidation process.