RECENT FIELD STUDIES in DYKE MARSH Soils Size Using the Hydrometer Method (Gee in August of 2003, an Orthophoto of and Bauder 1986)
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Recent Studies in Dyke Marsh Preserve In this section we discuss several studies that have taken place in Dyke Marsh since the early 1990s. This section will help us to understand the current knowledge that exists on Dyke Marsh, which can help us determine what still needs to be known. Some of the studies may also help provide insight into our primary concerns and fundamental questions for restoration in the discussion section. Soils 17-19 Elevation 19-21 Bathymetry 22-23 Hydrology 22 Water Quality 24 Tidal Gauge 24-25 Vegetation 25-28 1991 25-26 2003 25-28 2004 26-28 Relationship of Vegetation & Elevation 28-29 Seed Germination 29-35 Seed Trawls 29 Seed Bank 30-35 Invertebrates 35-36 Fish 36 Breeding Bird Surveys 36-37 Marsh Wren 37 Literature Cited 38 16 RECENT FIELD STUDIES IN DYKE MARSH Soils size using the Hydrometer Method (Gee In August of 2003, an orthophoto of and Bauder 1986). Most samples had DMP was used to select five transects higher than 70% organic matter, and all that traversed a diversity of vegetation samples had higher than 60%. Samples communities and topographic positions were composed largely of silt and clay, within the marsh. Soil core samples with little, if any, sand. Soil types were collected at the start, middle and include silty clay, silty clay loam, clay, end of each transect in March 2004 silt loam, and clay loam, with the (Figure 10). A total of 15 samples, each majority of samples being silty clay and 10-cm long, were analyzed for particle silty clay loam (Table 1 and Figure 11). Figure 10. Orthophoto of DMP with 5 transects used for soil cores and vegetation sampling. 17 Table 1. Particle-size analysis data of soil samples from DMP in March 2004. Organic Sample ID Location description Sand (%) Clay (%) Silt (%) matter (%) Soil Type near forest edge, dominated by TR1 B Impatiens and Peltandra 0 46 54 89 silty clay middle of marsh/ edge of Typha, dominated by Peltandra, Nuphar and TR1 M Typha 0 44 56 70 silty clay near river, dominated by Acorus and TR1 E Peltandra 12 38 50 72 silty clay loam TR2 B near river, dominated by Impatiens 20 45 35 84 clay middle of marsh, dominated by TR2 M Peltandra and Nuphar 6 39 55 74 silty clay loam near forest edge, dominated by TR2 E Nuphar 0 36 64 81 silty clay loam TR3 B near river, dominated by Impatiens 0 56 44 86 silty clay middle of marsh, dominated by Typha, Impatiens, Peltandra and TR3 M Nuphar 0 49 51 76 silty clay near forest edge, dominated by Typha TR3 E and Acorus 0 45 55 78 silty clay middle of marsh, dominated by TR4 B Phragmites and Peltandra 4 41 55 73 silty clay middle of marsh, dominated by TR4 M Impatiens and Typha 7 44 50 70 silty clay near wood buffer of Haul road, dominated by S. fluviatilis, Typha, TR4 E and Impatiens 0 71 29 79 clay near forest edge, dominated by TR5 B Impatiens 25 34 41 76 clay loam middle of marsh, dominated by TR5 M Peltandra, Bidens, and Sagittaria 17 28 55 62 silt loam middle of marsh, dominated by TR5 E Impatiens and S. fluviatilis 8 27 64 84 silt loam 18 100 90 80 70 60 Sand (%) Clay (%) 50 cent (%) Silt (%) r e P Organic matter (%) 40 30 20 10 0 TR1 B TR1 M TR1 E TR2 B TR2 M TR2 E TR3 B TR3 M TR3 E TR4 B TR4 M TR4 E TR5 B TR5 M TR5 E Sample ID Figure 11. Distribution of percent sand, clay, silt, and organic matter for each soil sample. Elevation were established, and from these Harper and Heliotis (1992) surveyed stations, 132 spot elevations were taken elevations of Dyke Marsh that they during low tide periods. incorporated into a hydrologic model of Elevation throughout the marsh was the marsh (see below). They surveyed found to be relatively flat with the spot elevations, using a Topcon exception of the tidal guts. Relatively Geodetic Total Station GTS-2 to flat areas of the main marsh occupy 93 establish horizontal and vertical control acres between elevations of 1.0 foot points in DMP. Four control stations (0.3 m) to 2.6 feet (0.8 m) (Figure 12). 4 3 2 1 Feet 0 -1 -2 0 20406080100120140 Acres Figure 12. Cumulative distribution of elevation at DMP (Harper and Heliotis 1992). 19 The Harper and Heliotis (1992) ft. included the spring tidal range of 0.0 hydrologic study also examined the to 3.0 ft. and extended from 2% to 99% elevations of 22 species along a of inundation time (Figure 13). These permanent transect throughout the results show that a variety of species marsh proper and along Hog Island Gut can coexist along an elevation gradient (Table 2). They found that the overall ranging from low marsh to high marsh. intertidal vegetation range of –0.5 to 3.3 Table 2. Elevation survey of DMP vegetation. Elevation range (ft) Elevation range (ft) Species (Harper and Heliotis 1992) (UMCES-AL unpublished) Acorus calamus 1.6 - 2.6 0.1 - 2.1 Amaranthus cannabinus 1.7 - 2.5 0.1 - 1.2 Apios americana -- 0.9 - 2.0 Bidens sp. 1.4 - 2.7 0.6 - 1.6 Boehmeria cylindrica -- 1.1 - 1.6 Calystegia sepium 2.3 - 2.7 0.8 - 2.0 Cephalanthus occidentalis 2.0 -- Cuscuta grovonii -- 0.9 - 2.0 Fraxinus sp. -0.2 - 2.4 -- Hibiscus moscheutos -- 1.3 - 1.4 Hydrilla verticillata -- -1.1 - 0 Impatiens capensis 1.7 - 2.8 0.5 - 2.1 Leersia oryzoides 1.7 - 2.7 0.9 - 1.7 Najas minor -- -0.4 - -0.1 Nuphar lutea -0.5 - 2.7 -1.1 - 1.6 Onoclea sensibilis -- 1.5 Peltandra virginica 0.3 - 2.8 -0.3 - 1.8 Phragmites australis 1.2 - 2.1 -- Pilea pumilia -- 0.9 - 2.0 Polygonum arifolium 1.5 - 2.7 0.9 - 2.1 Polygonum persicaria -- 0.1 - 1.6 Polygonum punctatum 1.4 - 2.1 0.6 - 1.0 Polygonum sagittatum -- 1.1 - 1.6 Pontederia cordata 1.2 - 1.7 0.1 Sagittaria latifolia 2.0 - 2.7 0.1 - 1.6 Scirpus fluviatilus 2.1 - 2.7 0.1 - 2.0 Sicyos angulatis -- 1.9 Sparganium americanum 2.7 -- Thalictrum polygamum 2.1 -- Typha sp. 1.2 - 2.8 0.1 - 2.1 Vitas sp. -- 1.2 - 1.6 Zizania aquatica 0.6 - 3.3 0.1 - 0.9 20 120 100 80 on i 60 dat nun 40 % I 20 0 -2 -1 0 1 2 3 4 5 E lev atio n (ft) Figure 13. Percent time of inundation for DMP elevations (Harper and Heliotis 1992). The UMCES Appalachian Lab surveyed the emergent marsh in July 2004. Topcon GPS equipment was used to obtain 129 spot elevations. Vegetation data consisting of percent cover of each species in a 1-m2 plot was also obtained at each of the 129 points (Table 2). A total of 27 species were observed throughout the marsh. The majority of these species were found in a broad range of elevations. Points surveyed ranged from -0.33 to 0.64 m in elevation. The majority of the points sampled throughout the marsh were between 0.25 and 0.49 m (Figure 14). Percent inundation time may be derived using the elevation data that Harper and Heliotis (1992) modeled (Figure 13). Researchers at UMCES Appalachian Lab will continue to work with modeling the 2004 elevation data in the near future. Specifically, they will model the effects of inundation frequency on plant community structure and incorporate scenarios of sea level Figure 14. Elevation ranges from point rise and freshwater pulses from the elevation survey, July 2004. watershed. 21 Bathymetry of DMP. Consultation with the USACE Much of the emergent marsh at can help to determine the approximate DMP lies on a plateau 3-4 ft. above amount of fill needed for a complete mean low tide and is not inundated by restoration of dredged areas, and the the typical 3 ft. tidal cycle. This shelf of timing, location and volume of future shallow water formerly extended Potomac River dredging operations that outward to the dredged shipping lane in match the fill needs of potential the middle of the Potomac River (NPS restoration projects at DMP. 1977). Two bathymetric surveys of DMP from 1974 and 1992 show the Hydrology underwater topographic pattern left by Harper and Heliotis (1992) designed sand and gravel dredging to be highly a hydrologic simulation model for Dyke variable with several deep holes (up to Marsh to enhance ecosystem 30 ft. below mean low tide) present monitoring and provide information for (Figure 15). Once past the dredged future restoration projects. They found area, the bottom contour apparently that the overall flushing rate per tidal recovers to a more shallow depth before cycle for the main marsh, based on reaching the 25-40 ft deep shipping values of mean low and high tide channel maintained by the U.S. Army volume was 0.92 m3/s. The highest Corps of Engineers (USACE). velocity was found along Hog Island Gut The 1992 bathymetric survey is now in the mid channel (21-35 cm/s), 12 years old and likely not entirely although tidal velocity was not observed accurate owing to natural causes such to be disruptive to inter-tidal vegetation. as sediment scouring and deposition Mean tide ranged between 0.2 and 2.8 over the years and also due to extensive feet, with an average of 1.5 feet.