Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 12/10/1998
Publication Date: N/A
Technical Abstract: Soil CO2 efflux rate (soil respiration) was measured during the snow-free dormant season on forest and agricultural (conventional-tillage soybeans) loess-derived soils in Mississippi and Iowa. Efflux rates were measured periodically with a non-steady state chamber technique using an infrared gas analyzer. Differences in the response curves for CO2 efflux as a function of soil temperature among sites were related to landscape position, soil organic carbon (SOC), and land use. CO2 efflux rates increased faster with increasing temperature in toe slope positions compared with hillslope positions at most sites. In agricultural watersheds, toe slope positions had higher SOC than hillslope positions and higher CO2 efflux rates over most of the measured temperature range. In contrast, in two forested watersheds, CO2 efflux rates were similar between toe slope and hillslope positions over the observed temperature ranges. In none forested watershed, SOC levels were similar between toe slope and hillslope positions. In another forested watershed, the toe slope positions had higher SOC than the hillslope position. Soil temperature-CO2 efflux response curves showed lower soil CO2 efflux rates in agricultural watersheds in Iowa than in Mississippi at both landscape positions. Long-term measurements of sediment export rates in Mississippi watersheds indicate that sediment export is about two orders of magnitude greater in agricultural compared with forested systems. Higher CO2 efflux rates in toe slopes on agricultural watersheds may be partially explained by the internal redistribution of soil eroded from hillslopes and deposited in toe slope positions within the watershed. Toe slope positions may also support higher plant productivity and associated organic carbon inputs to soils.