Do erosional and depositional processes in agricultural landscapes sequester carbon?

Abstract

There are many reasons for reducing erosion in agricultural landscapes, but there has yet to be a definitive answer as to whether carbon sequestration is among them. Previous studies have shown that agricultural erosion is neither a sink nor source of soil organic carbon (SOC) categorically; rather, it may vary between the two depending on field conditions and management practices. This study sought to better understand the effects of soil movement mechanisms on SOC by combining measurements of SOC and 137Cs (produced during atmospheric testing of nuclear bombs in the 1960s). As a radioisotope, this nuclear fallout becomes strongly adsorbed to soil particles and functions as a conservative tracer for soil movement over the past approximately 50 years. For this study, soil samples were collected from both croplands and grasslands in southeastern Minnesota. Preliminary results show a 137Cs/SOC ratio in cropland soils that is consistently less than the observed ratio for grasslands, suggesting that despite erosional tendencies, agricultural soils are preferential SOC sinks. Overall, the data suggest that SOC is effectively sequestered via burial due to erosional and depositional processes, rather than physically decomposed to be lost as CO2.