Vegetation and Soil Nutrient Dynamics, and Carbon Sequestration Potential at Central Wisconsin Wetland Restoration Locations
Besasie, Nicholas J.
University of Wisconsin-Stevens Point, College of Natural Resources
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Wetlands provide many valuable functions on the landscape, but many wetlands have been severely altered over the last two centuries by changes in land use. Farm bill programs such as the Wetland Reserve Program (WRP) and Conservation Reserve Program have allowed wetlands to be restored or protected. Studies have indicated overall landowner satisfaction with the programs, but scientists have not done significant monitoring to determine if the wetlands are functioning properly. This study seeks to evaluate the state of wetland restoration attempts in central Wisconsin and establish baseline data to enhance and enable future comparison. Two separate investigations into the success of wetland restorations were conducted. In the first investigation to better understand the success of restoration attempts, two young restorations and a native wetland were surveyed for vegetation, soil physical characteristics (bulk density, depth of organic rich horizons), and soil nutrient levels (nitrogen [N], phosphorus [P], sulfur [S], and carbon [C]). Analysis revealed that vegetative communities differed between native and restored wetlands, with native wetlands having the greatest biodiversity and species richness. However, planting of vegetation appears to increase biodiversity and vegetative community structure within restorations. Comparison of soil physical parameters demonstrated that native wetlands have deeper organic horizons and lower soil bulk density. Analysis of soil nutrient levels showed that native wetlands overall have greater and less varied amounts of N, S, and C. The historical shift of native wetlands to agriculture has lead to the depletion of organic soil carbon. Restoring wetlands may shift carbon from the atmosphere back to the soil. The second part of this study seeks to quantify the amount of organic soil carbon that has accumulated since restoration of WRP sites. Composite soil samples have been taken from 32 different WRP sites (varying in age from pre-restoration to 16 yrs post restoration) located in Central Wisconsin. The success of the restoration efforts, in terms of organic soil carbon content, were determined through comparison to several undisturbed wetlands within the same geologic area. The soil organic carbon (SOC) concentration was quantified through combustion of organic materials using a Carbon and Nitrogen Analyzer. Soil organic carbon concentration levels were highly variable throughout the study area (22 to 305 g kg-1). A weak positive correlation (r^2 = 0.28) between SOC concentration and time since restoration at WRP sites with histosols or histic epipedons was discovered. No significant trend was found for total carbon content of the soil profile and time at WRP locations. Depth of organic rich horizons appears to be limiting the recovery of SOC content. Given the relatively young age of the restorations in this study it is possible that the level of pre-restoration disturbance is still the dominating factor determining SOC levels.