Effect of Growing Season on the Criterion for Wetland Hydrology

A study was conducted to determine effects of using two different methods of approximating the growing season (GS) on the hydrology of lands that satisfy the wetland hydrologic criterion. The two GS considered were the frost-free GS defined by medium dates of 28 A degrees F air temperatures (28F), and a 365-day GS (365D) based on soil temperature. Analyses on 5 hydric soils near Plymouth, NC showed that using the 365D rather than the 28F GS will substantially reduce saturation requirements for wetland hydrology. A site that would have a water table within 30 cm of the surface for a continuous period of 14 days or more in 50 % of the years during a 365D GS would satisfy the same criterion for only 4 % of the years during the 28F GS; it would have water table less than 30 cm deep for a continuous period of only 7 days in 50 % of the years during the 28F GS. Use of the 365D rather than the 28F GS would substantially reduce saturation requirements at the wet end of the wetland hydrology spectrum (12.5 % of GS) which is typically required for wetland restoration in mitigation projects. Research is needed to develop a scientifically rigorous criterion for wetland hydrology.