Organic soil subsidence

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Abstract
Organic soil subsidence occurs mainly with drainage and development of peat for agriculture. Subsidence occurs either from densification (loss of buoyancy, shrinkage, and compaction) or from actual loss of mass (biological oxidation, burning, hydrolysis and leaching, erosion, and mining). Densification usully occurs soon after drainage is established. Slow, continuous loss of mass is due mainly to biological oxidation. Erosion is minor except in specific sites. Mining losses vary greatly and depend upon direct removal of the materials. Subsidence rates are determined mainly by type of peat, depth to water table, and temperature. Subsidence losses have been carefully measured in several locations (e.g., the Florida Everglades), and predictions of future subsidence developed in 1950 have proved reliable. Peat drainage and subsidence have several consequences: loss of plant rooting depth where the substrate is unfavorable (stony, acidic, saline), increased pumping for drainage, instability of roads and other structures, increase in nutrient outflows, colder surface temperature during winter nights, and increase of CO2 flux to the global atmosphere The water table for organic soils should be held as high as crop and field conditions allow to reduce subsidence. Computer models offer methods for refining oxidation rate processes and prediction of subsidence losses where adequate calibration data are available. Remote sensing offers a method of assessing organic soil area and drainage changes. These new technologies should improve our assessment, and guide our management, of organic soil resources.

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