Spring 2008 Seminar Series

W. Lee Daniels

Abstract

Construction of created non-tidal wetlands to mitigate for highway impacts usually requires more than $100,000 per ha of impact. A detailed study of soil, hydrologic, and vegetation parameters at 10 recently constructed VDOT non-tidal mitigation sites indicates excessive soil compaction and a lack of organic matter continue to limit mitigation success. Detailed hydrologic studies at two mitigation sites (Charles City and Sandy Bottom) pointed out significant differences in their hydrologic regime vs. adjacent natural wetlands related to soil reconstruction procedures. Results from two compost amendment experiments at Charles City indicated that approximately 100 Mg/ha of organic amendment is optimal for reconstructing hydric soil conditions when natural organic enriched soil materials cannot be returned.  A parallel field plot study at Shirley Plantation has revealed significant effects of installed micro-topographic variability on early growth and vigor of Taxodium distichum L. (bald cypress), along with further support for the use of organic amendments to favor establishment of herbaceous wetland vegetation. Overall mitigation success would improve from (1) utilization of appropriate organic amendments, (2) tillage/ripping protocols at all sites to meet target density specifications, and (3) reconstruction of a soil-geologic profile that is similar in texture and permeability to natural wetland soils.