Diurnal and seasonal CO2-C flux from soil as related to erosion phases in central Ohio

The CO2-C flux from soil is an important part of the global C cycle, whose dependence on erosion is as yet largely unknown. We hypothesized that the magnitude of diurnal and seasonal C flux is related to soil erosion phase and is influenced by soil water and temperature regimes. The CO2-C flux from the surface of a Miamlan silt loam soil (fine, mixed, active, mesic Oxyaquic Hapludalf) in central Ohio was monitored using the static chamber method. Gas samples were collected four times daily (at 0900, 1200, 1500 and 1800 h) at approximate to 2-wk intervals between July 1995 and June 1997, The CO2 evolved from the soil surface varied significantly among seasons ranging from 0 g C m(-2) d(-1) in the winter to approximate to 1.6 g C m(-2) d(-1) during the summer. Soil erosion phase had no direct effect on C flux from the soil, although depositional areas had 20 to 25% higher water content than other phases, while severely eroded and depositional areas generally had higher soil temperatures than slightly and moderately eroded phases. Soil C flux exhibited diurnal variations with high values differing from lows by as much as 0.04 g C m(-2) h(-1). Peak flux rates as high as 0.082 g C m(-2) h(-1) occurred during the mid afternoon during the spring, summer, and autumn seasons. Soil C flux was significantly correlated with soil temperature (r(2) = 0.804) and air temperature (r(2) = 0.806) but not with soil moisture content.