A baseline data study of the hydrologic regime and wetland plant communities at Hackett Hill, Manchester, New Hampshire

Hall, Kimberly Paige
Jon Atwood, PhD
Department of Environmental Studies
There were three primary objectives of this study: 1) to document the hydrologic regime for selected Atlantic white cedar, Atlantic white cedar/giant rhododendron, black gum, and red maple swamps on the Hackett Hill property in Manchester, New Hampshire; 2) to document dominant species within the plant communities; and 3) to define a qualitative water budget for each of the three watersheds that encompass the study area. The Hackett Hill Property at the time of writing this document was subject to potential development in the upland surrounding these wetland basins; therefore, it was the intent of this research to provide baseline data documenting existing hydrological conditions and plant community composition within these wetland basins under predevelopment conditions. Previous studies have determined that nearby development can alter wetland hydrology and that the plant communities that comprise these wetland basins have been found to be extremely sensitive to changes in the hydrology of their respective watersheds. To obtain data on existing hydrologic regime for each of the three subwatersheds that contain the plant communities of primary concern, 23 piezometers were installed in seven (7) transects located throughout each of the four wetland basins containing the plant communities of interest to this study. A wetland basin containing a red maple swamp was included in the study as a measure of comparison. The water level at each piezometer was measured once every two weeks for the period of one year to obtain data for one complete hydroperiod. The results of water table monitoring were analyzed to mean water level, water table fluctuation, and inundation/hydroperiod. A one-time vegetation sampling event inclusive of three vegetative strata (ground cover, shrubs, and trees) at each of the 23 monitoring points (piezometer) was conducted. The ground cover and shrub strata were sampled using one (1) and three (3) meter box plots, respectively. The tree stratum was sampled using a five-factor prism. All vegetation sampled was documented and species dominance was determined based upon percent areal coverage, basal area, and density. Dominant species were then assessed and analyzed with respect to mean water level using R² regression analysis to observe trends in species occurrence and “wetlandness.” It is hoped that the monitoring plan set forth in this study and data that has been collected will provide the foundation upon which future long-term hydrological and ecological studies can be based fro the Hackett Hill Wetlands and other ecologically comparable wetlands.

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