Conference Name: Geological Society of America Conference 2011
MULLING, Adam D.1, HOWARD, Samuel M.1, and COLGAN, Patrick M.2, (1) Geology, Grand Valley State University, 118 Padnos Hall of Science, Allendale, MI 49401-9403, email@example.com, (2) Geology, Grand Valley State University, 132 Padnos Hall of Science, 1 Campus Drive, Allendale, MI 49401-9403
Humans cause erosion through deforestation, urbanization, and poor agriculture practices, filling many stream valleys with sediment and storing soil organic carbon (SOC). This project has two primary goals: first, to estimate the mass of SOC in post-settlement (~1830 CE) alluvium in Ottawa County; and second, to calculate the rate of deposition and SOC storage since 1963 to 1964. About 230 samples were collected in stream valleys filled with the Sloan Loam. Percent SOC was estimated by the loss on ignition method, and using a calibration curve developed for fine textured glacial parent materials. Cesium-137 activity in soil profiles was measured to estimate the thickness of sediment deposited since 1963 to 1964.
Our preliminary data show that mean percent SOC in the Sloan Loam is 2.0 ± 2 %, and dry densities averaged 1300 ± 230 kg per m3. Sloan Loam covers an area in Ottawa County of about 2.4 x 107 m2. Thickness of post-settlement sediment ranges from 0.5 to 2 meters, yielding 1.2 to 4.8 x 107 m3 of sediment in Ottawa County. We estimate that a total mass of 0.3 to 1.3 x 106 tonnes of carbon has been stored in the Sloan Loam in Ottawa County since settlement (~1830 CE). The thickness of sediment deposited since 1963 to 1964 in three profiles is about 180 mm, 360 mm, and 500 mm based on Cesium-137 activity. This yields a sediment deposition rate of 3.8 to 10 mm per year, or a rate of SOC storage of approximately 2.4 to 6.5 x 103 tonnes per year in the Sloan Loam. Our data demonstrate that post-settlement alluvial soils contain significant stores of SOC.