The Influence of Agricultural Drainage Practices On Carbon Emissions From Cultivated Organic Soils in Kankakee River Basin, Indiana.

Widespread drainage of organic soil in the Kankakee River basin in northern Indiana for agriculture has significantly altered hydrological pattern as well the carbon balance since mid-1800s. Over 80% of natural wetland areas were drained to facilitate better crop production through agricultural managements including surface (ditch) and subsurface (tile) drainage applications. Most of cultivated organic-rich soils in this basin contain at least 20-30% organic matter by weight with highly variable depth. The water table position acts as the dominant control on CH₄ and CO₂ emissions and the soil organic matter can be switched from a net C sink to a source. Lower water tables caused by drainage generally increase CO₂ emissions and reduce atmospheric CH­₄ fluxes. Lowering the water table depth by artificial drainage may have significantly affected the rate of subsidence and decomposition of these soils but the size of the effect is not yet known.

We have attempted to quantify the influence of water management on carbon dynamics on cultivated organic soils in this study. To approach this, the Variable Infiltration Capacity (VIC) macroscale hydrologic model has been modified to represent net primary productivity, sub-field variability in water table position, and subsurface drainage. Methane and carbon dioxide emissions are simulated using soil temperature, water table position and NPP generated from the VIC model and evaluated using field CO₂ flux measurements from a site in Pulaski, IN, combined with periodic measures of water table height and soil moisture and temperature from May to October 2006. Long term simulation at the watershed scale is used to estimate the drainage rates and carbon emissions for the region under different drainage intensities. This study concludes that cultivated organic soil under the intensive drained management has significantly higher CO₂ emission rate, net subsidence and C source compared to undrained management.