Carbon Sequestration Potential at Central Wisconsin Wetland Reserve Program Sites

Abstract

Wetlands provide many valuable functions on the landscape; however, many wetlands have been drained over the past two centuries. The historical shift of native wetlands to agriculture has led to the depletion of soil organic carbon (SOC). Restoring wetlands may shift C from the atmosphere back to the soil. Farm bill programs such as the Wetland Reserve Program (WRP) have helped restore some farmed wetlands. This study seeks to quantify the amount of SOC that has accumulated since restoration of WRP sites. Composite soil samples were taken from 32 different WRP sites (maximum age of restoration was 17 yr) located in central Wisconsin. The success of the restoration efforts, in terms of SOC content, was determined through comparison to several undisturbed wetlands within the same geologic area. The SOC concentration was quantified through combustion of organic materials using a C and N analyzer (Costech Analytical Technologies Inc., Valencia, CA). Soil organic C concentration levels varied from 20 to 362 g kg−1 with a weak positive correlation (r2 = 0.26) between SOC concentration and time since restoration at WRP sites with histic epipedons. No significant trend was found for total SOC content and time since restoration. It appears that bulk density and depth of organic rich horizons are the components of total SOC content that are recovering slowly and causing the low correlation for SOC content. Given the relatively young age of the restorations in this study it is also possible that pre-restoration factors (such as disturbance level) are affecting SOC levels.