Browsing by Author "Speiran, Gary K."
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- Evaluation of Methods to Calculate a Wetlands Water BalanceDaniels, W. Lee; Cummings, Angela R.; Schmidt, Mike; Fomchenko, Nicole; Speiran, Gary K.; Focazio, Mike; Fitch, G. Michael (Virginia Center for Transportation Innovation and Research, 2000-08)The development of a workable approach to estimating mitigation site water budgets is a high priority for VDOT and the wetlands research and design community in general as they attempt to create successful mitigation sites. Additionally, correct soil physical, chemical and biological properties must be restored that are appropriate to the intended wetlands biota in order for the sites to function similar to a natural sites that they are replacing. The major objectives of this research program were to evaluate the currently recommended procedures for estimating wetland water balances and to characterize the soil and hydrologic regime present at natural and constructed sites and their interaction with wetlands biota. This report records our efforts to develop an estimated overall water budget at VDOT's Ft. Lee mitigation site along with a summary of our previous water budget studies at Manassas. Detail on supporting studies is also provided along with an overall summary of multi-year research results and implications. In this report, the terms water balance and water budget are used almost interchangeably. In our view, however, water budgets are developed by humans to interpret actual wetland water balances. It was concluded that the use of the Pierce (1993) approach for developing mitigation wetland water budgets is prone to a number of errors in surface water charging estimates and ET estimates via the Thornthwaite method. The Pierce approach is most appropriate for estimating water budgets in surface water driven emergent/shrub-scrub systems with little ground water flux that rely upon berms or other water control structures to detain and pond water over impermeable soils or strata. Additionally it was found that the development of soil redox features, particularly the quantity and distinctness of oxidized rhizospheres can be reliably used to interpret hydric soil development sequences in mitigation wetlands. However, the reestablishment of an appropriate mitigation site wetness regime to one that appears to meet jurisdictional wetness criteria will not always guarantee the success of desirable hydrophytic vegetation over time.
- Linking ecosystem function and hydrologic regime to inform restoration of a forested peatlandSchulte, Morgan L.; McLaughlin, Daniel L.; Wurster, Frederic C.; Balentine, Karen; Speiran, Gary K.; Aust, W. Michael; Stewart, Ryan D.; Varner, J. Morgan; Jones, C. Nathan (2019-03-01)Drainage is a globally common disturbance in forested peatlands that impacts peat soils, forest communities, and associated ecosystem functions, calling for informed hydrologic restoration strategies. The Great Dismal Swamp (GDS), located in Virginia and North Carolina, U.S.A., has been altered since colonial times, particularly by extensive ditch networks installed to lower water levels and facilitate timber harvests. Consequently, peat decomposition rates have accelerated, and red maple has become the dominant tree species, reducing the historical mosaic of bald cypress, Atlantic white-cedar, and pocosin stands. Recent repair and installation of water control structures aim to control drainage and, in doing so, enhance forest community composition and preserve peat depths. To help inform these actions, we established five transects of 15 plots each (75 plots total) along a hydrologic gradient where we measured continuous water levels and ecosystem attributes, including peat depths, microtopography, and forest composition and structure. We found significant differences among transects, with wetter sites having thicker peat, lower red maple importance, greater tree density, and higher overall stand richness. Plot-level analyses comported with these trends, clearly grouping plots by transects (via nonmetric multidimensional scaling) and resulting in significant correlations between specific hydrologic metrics and ecosystem attributes. Our findings highlight hydrologic controls on soil carbon storage, forest structure, and maple dominance, with implications for large-scale hydrologic restoration at GDS and in other degraded forested peatlands more broadly.