Development of Soil and Site Reconstruction Guidance for Created Non-Tidal Wetland Sites in the Mid-Atlantic USA.

Many non-tidal wetlands created before 2000 in the mid-Atlantic USA exhibited adequate site hydrology (hydroperiod), but were plagued by a combination of high soil bulk density, low organic matter levels and other inter-related factors which limited development of appropriate soil biogeochemical conditions and associated hydrophytic plant species.  However, many of these earlier created wetlands also suffered from an inappropriate hydroperiod due to (a) excessive groundwater discharge leading to long-term ponding, or (b) compaction of subsoil layers creating unusual localized epiaquic conditions, or (c) inappropriate dry upland locations.  In several replicated field experiments, we noted dramatic increases in soil redoximorphic features in response to tillage and compost additions. Bald cypress (Taxodium distchum L.) also responded significantly to installation of micro-topography (e.g. pits and mounds). Overall survival and performance of woody tree species is most strongly affected by recreation of an appropriate hydroperiod and soil physical properties and less affected by organic matter additions.  To maximize wetland creation success, appropriate site water budgeting procedures must be applied that account for hydrogeomorphic setting and associated groundwater fluxes. This requires some level of pre-construction groundwater monitoring.  Next, pre-construction soil morphology, chemical and physical properties must be detailed and then described again after soil reconstruction to establish baseline comparative conditions. Post-construction subsoil bulk density should not exceed 1.45 Mg/m³ for fine textured soils and 1.75 Mg/m³ for coarser textures, and should be corrected by tillage as necessary. If returned topsoil is low in organic matter, or not available, suitable organic amendments should be added at moderate rates (< 75 Mg/ha). Finally, micro-topography should be installed to mimic local conditions, and locally available organic litter and woody debris should be surface-applied.  Implementation of these procedures can be greatly complicated by certain wetland designs, particularly those involving heavily compacted subsurface zones without suitable rooting depth.