Tuesday, November 14, 2006

An Explanation of the Hydric Soil Technical Standard and Normal Precipitation.

G. W. Hurt, Univ of Florida, PO Box 110290, Gainesville, FL 32611-0290 and M.J. Vepraskas, North Carolina State Univ, P.O. Box 7619, Raleigh, NC 27695-7619.

Field Indicators have been developed for on-site identification of hydric soils. These indicators have been established by combining the best professional judgment of practicing wetland soil scientists with data generated by participating research soil scientists. In most cases, soils with a field indicator are hydric and soils without a field indicator are nonhydric. However, in some instances a soil with an indicator may not, in fact, meet the official definition of a hydric soil. Conversely a soil without an indicator may, in fact, meet the definition. Therefore, it is necessary to have a technical standard based on soil measurements that reflect the hydric soil definition. The National Technical Committee for Hydric Soils (NTCHS) has developed specific requirements for measurement of saturation, reduction/oxidation potential, reduced iron (Fe++), in-situ pH, and on-site precipitation data. The technical standard for hydric soils establishes threshold value requirements and instrumentation methodology for data collection. Guidelines have been developed by the NTCHS for the interpretation of each data set. To be most useful for improving the field indicators or proving the hydric status of a specific site, the data must be collected during Anormal@ precipitation months. There are several NTCHS approved methods for computation of “normal” precipitation and examples will be presented.