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Home My WebLink About20081615 Ver 4_Monitoring Plans_20131231Topsail Beach Winter 2013 Nourishment Project Final Biological Monitoring Plan — December 2013 Town of Topsail Beach Purpose This plan outlines biological monitoring offered by the Town of Topsail Beach as part of its Winter 2013 Nourishment Project and in association with proposed excavation in adjacent federally - maintained channels. The goal of this plan, in combination with physical monitoring conducted as part of the Town's storm damage reduction and long term management plan, is to assess whether any appreciable biological effects result from the increased dredge depths and widths proposed by the project. As part of the proposed action, the Town intends to obtain beach compatible sand from the adjacent federally- maintained channels of New Topsail Inlet, Topsail Creek, the Connector Channel between the inlet and Topsail Creek, and Banks Channel. Since the proposed width and depth in New Topsail Inlet and Topsail Creek would exceed federally- authorized dimensions, this biological monitoring plan is designed to assess whether proposed dredging will impact biological resources important to fisheries and the estuarine system. Biological Monitoring Components In New Topsail Inlet and the Connector Channel, the federally- maintained channel abuts subtidal, sandy bottom and un- vegetated, intertidal sand flats. Due to the nature of these habitat areas, any changes in intertidal shoals at the mouth of the inlet will be best assessed by the physical monitoring program. Historic aerial photographs, annual aerial photography updates, and annual hydrographic surveys will describe and quantify any shoaling changes at the mouth of the inlet. Given the naturally dynamic nature of the inlet system, there is limted coastal marsh directly adjacent to these sections of channel. Benthic infauna present in shallow subtidal bottom and intertidal shoals adjacent to the dredge area are expected to quickly colonize any shifting shoals. Source sediment for any changing shoals will be native sands and would not be the result of man- made deposition or incompatible sediment. Therefore, benthic infauna are expected to recover at natural rates in these areas. For this reason, no biological sampling is proposed along the New Topsail Inlet or the Connector Channel where physical sampling will be more descriptive. Biological Monitoring Plan 1 Winter 2013 Nourishment Project Town of Topsail Beach Proposed dredging in Banks Channel will not exceed authorized federal depths, and no biological monitoring is proposed along this channel. It is noted that Banks Channel is also included in the physical monitoring program. The back barrier marsh complex along Topsail Creek is typical of the region and consists of tidally inundated salt marsh occuring in patches along a network of small tidal creeks. Marsh exists almost entirely in the low marsh position and is dominated by Spartina alterniflora. Along the southeastern edge of the mouth Topsail Creek (the edge of the complex facing the inlet) a narrow sandy beach and limited shrub hammock is present (Figure 1). Ecosystem state change from low marsh to intertidal flats, or intertidal flat to shallow subtidal bottom, is expected to occur on a relatively slower temporal scale than at the mouth of the inlet due to resistance of the vegetative structure. Due to the extent of natural variability associated with the inlet and its immediate environs, biological sampling will occur within the interior marsh complex and adjacent to the proposed dredging channel alignment in Topsail Creek. In addition, the Town's long term physical monitoring program, particularly the aerial photography, will capture any spatial changes in the overall marsh -creek complex. Since dredging would occur largely within the footprint of existing federally- maintained channels, monitoring will be conducted in areas directly adjacent to, rather than within, the excavation area. Sampling efforts will focus on biological and physical conditions that are most likely to be affected by dredging and any altered flooding regime or sedimentation. Any effects on tidal marsh would be expected to manifest in system responses distributed linearly from Topsail Creek. Therefore, the biological monitoring plan proposes to sample along transects extending from the channel of Topsail Creek into the adjacent marsh /creek complex on the western side nearest the channel (Figures 2 and 3). Parameters to be sampled relate to marsh structure, the benthic infauna community, and physical sediment characteristics. Low marsh areas intermixed with small tidal creeks are known to provide cover and feeding areas for juvenile fish, and marshes in this area do function as nursery areas. Marsh biomass is also an important contributor of organic matter to the estuarine system, supporting the system's overall primary productivity. Sampling marsh density and stem height will quantify any changes in Biological Monitoring Plan 2 Winter 2013 Nourishment Project Town of Topsail Beach biomass or structure, and the data will be evaluated in conjunction with any changes apparent in aerial photography. Benthic infauna are often utilized as a potential indicator of biological health in estuarine communities, particularly in response to natural or human - induced changes. Characteristics of benthic infauna that make them particularly well- suited for samping include their low motility and close association with sediment substrates. Benthic infauna are important sources of food for fish and birds, and play an important role in the transfer of energy to higher trophic levels. For these reasons, the benthic infauna community will be sampled for abundance and species diversity. Sediment samples will also be collected to quantify any changes in sediment texture (changes in percent sand and organic matter) that may result from erosion or deposition. Sampling Plan and Methodology Six sampling transects have been identified on the western shore of Topsail Creek along the section of channel between transects 38 +00 and 45 +00 (application Sheet 17 of 28). The section of channel along Topsail Creek between channel transect 62 +00 and 46 +00 abuts that portion of the back barrier complex with a sandy beach and shrub hammock. Since these features are expected to provide protection to marsh areas behind them, sampling transects were not aligned along this section of channel. The western side of the creek was chosen for sampling since the channel is aligned closer to this side. Sampling transects would be located roughly at channel transects 45 +00, 44 +00, 41 +00, 39 +00, 38 +50 and 38 +00 (Figure 3). These transects will be labeled TC1, TC2, TC3, TC4, TC5, and TC6, respectively. Transects would begin at the edge of the marsh abutting the channel and extend 300 -ft into the marsh. Five sampling stations will be established along each transect, and would be located at 5, 50, 100, 150 and 300 feet away from the edge of Topsail Creek. The station located furthest from Topsail Creek (300 -ft) will serve as the control plot for each transect. Exact transect locations will be finalized based on field- specific conditions during pre- construction monitoring. For example, a transect location maybe refined if a sampling station occurs within open water rather than the target low marsh habitat. Transects and sampling stations will be located on a geo- rectified aerial and uploaded on a mobile GPS unit for location in the field. Biological Monitoring Plan 3 Winter 2013 Nourishment Project Town of Topsail Beach Parameters to be sampled along the transects will include: (1) Spartina stem density (2) Mature ( >30 cm height) Spartina stem height (3) Distance (ft) loss or gain of intertidal marsh habitat at transect locations (4) Percent sand, silt, and clay of surface substrate (5) Percent organic content of surface substrate (6) Benthic infauna abundance and (7) Benthic infauna species. In addition to the identified quantitative sampling, qualitative observations of marsh and/or intertidal habitat will be noted. One -meter square quadrats will be sampled for stem density and height range of S. alterniflora at each station. Stem heights will be grouped in categories based upon pre- determined ranges (30- 60 cm, 60 -90 cm, 90 -120 cm, >120 cm). Each height range will be assigned a value (1, 2, 3, and 4, respectively). The number of stems in each category will then be multiplied by the corresponding height value to obtain a height index. Cumulative height indices for each quadrat will be calculated and recorded. Sediments will be characterized according to percent sand /silt /clay and percent organic matter (OM). One sediment sample will be collected at each of the fixed stations (5, 50, 100, and 150, and 300 -ft plots). Sediment samples will be transferred to A &L Agricultural Labs (Richmond, VA) for particle size analysis and OM by combustion. Benthic infaunal will be sampled at three observation points (i.e. at 5', 150', and 300' from creek edge) along three of the six transects (TC2, TC4, and TC6) (N =27). Three replicates of 15 cm- deep cores (10 cm diameter) will be collected within 10 -ft of the permanent vegetative quadrat at a randomly - generated bearing. Individual core samples will be transferred to sample bags and labeled. Samples will be fixed using a 10% formalin solution and sieved through a 0.5 mm screen mesh to separate infauna from sediment and vegetative material. All samples will be transferred to UNCW- Center for Marine Science benthic laboratory or to a similarly qualified benthic ecologist for processing and identification. Benthic infaunal organisms will be enumerated and identified to the Biological Monitoring Plan 4 Winter 2013 Nourishment Project Town of Topsail Beach lowest reliable taxonomic level. Additional statistical analyses may be performed for species richness and diversity. Diversity will be calculated using the Shannon Weiner Diversity Index. Sampling will be done at the end of the growing season between September and early October of 2013. It is recommended that annual sampling at the end of the growing season continue until the next dredging event is required, at which time, existing data will be evaluated for any trends and further data collection needs can be reassessed. 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