Mapping & Surveying: Monitoring the Active Replenishment of Subsiding Habitat Project (MARSH) - Vegetation Survey
The objective of this research is to determine whether a layer of sediment sprayed over the marsh to increase the surface elevation will result in a change in the existing plant communities within portions of the Lee and Hill marshes, which have been recently dominated by arrow arum (Peltandra virginica ).
During the early summer of 2001, replicate transects were established at three locations within the study area; one within Lee marsh (Lee-1) and two within Hill marsh (Hill-east and Hill-west). Transects within Lee marsh where established adjacent to one of the larger tidal creeks running through the marsh. Transects within the Hill-west site were established adjacent to the Pamunkey River while transects within the interior Hill site (Hill-east) were established approximately 200m from the river. Five, 50 meter (m) transects where established early in 2001 at each study site. Transects where aligned parallel to the source of hydrology and placed 10m apart. The odd numbered transects were labeled A, B, and C and sampled using 1m 2 quadrats placed every 5m along their entire length. Sampled plots where randomly selected on either the left or right side along the transect to remove any sampling bias. Percent cover (total amount of vegetation found within each quadrat) was recorded along with the percentage of each species comprising the total vegetated portion of each quadrat. VIMS scientists identified plants in the field to the maximum extent possible and species level identifications were later determined or confirmed in the lab when possible.
Vegetative sampling of the three sites was first conducted during July and August of 2001 prior to the application of the spray dredge material. The purpose of this initial sampling was to characterize the existing plant communities within each site. This information also provided baseline data for future comparison of plant communities following the disturbance associated with the application of the spray dredge material. Surface elevation data for each site was also collected during the summer of 2001 prior to disturbance using a Trimbell Ò Global Positioning System (GPS). Initial data show all three study sites where dominated by arrow arum although sedge (Carex comosa) and giant cordgrass (Spartina cynosuroides) comprised a major percentage of numerous plots within the Hill-west and Lee sites respectively. Wild rice (Zizania aquatica) comprised a large percentage of quadrats within the Hill-east interior site.
Following the application of the spray dredge material in early October 2001, a second survey of surface elevations was conducted at each site. Although the average accumulation of dredge material on the marsh surface at each site was less than 10 in., VIMS scientists were interested in whether the increased surface elevation would result in a change of the dominant plant species. The objective was to convert an arrow arum marsh to habitat dominated by another plant species more valuable to waterfowl, such as a wild rice and/or giant cordgrass marsh.
VIMS scientists recently conducted the first of several samplings planned during the second year of the vegetative community study. For direct comparison, the same 50-m transects and sample plots established last year during the initial sampling protocol were utilized. Data collected during the 2002 early season sampling show that arrow arum remains the dominant plant species found within each of the three sample sites, while sedge and giant cordgrass continue to comprise a large percentage of the quadrats sampled at the Hill-west and Lee marsh sites respectively. Although early season 2002 data (post-spray dredge) appear to indicate no significant change in the plant communities within the three sample sites, VIMS scientists will conduct additional sampling later this summer and continue to evaluate whether species such as wild rice and giant cordgrass increase in abundance in the experimental area. Another post-dredge physical survey will also be conducted later this summer to determine the relative permanence of artificially raising the elevation of the marsh surface. It is hoped that our continued study will provide valuable insight into the feasibility of successfully altering an existing plant community with the application of sprayed dredge material or that when performed correctly, this technology represents an acceptable method for the disposal of dredged material without long-term adverse environmental effects.
|
