Use of Field Indicators of Hydric Soils to Characterize Slope Wetland Hydroperiods and Water Quality Services.

A signature characteristic of an individual wetland is its hydroperiod for it impacts the wetland functions related to biogeochemical cycling, water retention, plant community composition, and wildlife habitat. Wetland assessment for functional capacity or condition is conducted to characterize a state’s wetlands, or for purposes of wetland mitigation, restoration, or enhancement. Hydroperiod characterization has relied on monitoring wells to assess water table depths. This approach is either expensive, time consuming, or both. Field Indicators of Hydric Soils were developed to assist in jurisdictional determinations of wetlands. Conceptually, hydric soil indicators reflect long-term hydrologic conditions, and their presence in an individual soil does not change in response to individual years of above- or below-normal precipitation. Although intended to determine whether a soil is hydric, Field Indicators represent soil morphologies that develop under a range of hydrologic conditions. Therefore, a study was conducted in the mid-Atlantic Piedmont Region, U.S.A. to evaluate the potential use of Field Indicators to (i) characterize hydroperiods beyond the standard jurisdictional criteria and (ii) assess the capacity of wetlands to remove nitrate and orthophosphate from the water column. Twenty-one slope wetlands were assessed for water table depths (twice daily for a minimum of 39 months) and presence of Field Indicators. Seven Field Indicators were identified. A six-site subset was chosen for intensive water sampling for nitrate and orthophosphate. The sites were chosen to represent a range of hydrologic conditions and a range in potential nutrient loading. Some Field Indicators were consistently associated with specific hydroperiod classes (permanently-inundated, permanently-saturated, and seasonally-saturated) and characteristic water table fluxes (static or dynamic). Efficiency of nitrate and orthophosphate removal was associated with Field Indicators F3. Depleted Matrix and A11. Depleted Below Dark Surface., which in turn were associated with dynamic water tables.