The Distribution of Submersed Aquatic Vegetation in the Fresh and Oligohaline Tidal Potomac River, 2004 By Nancy B. Rybicki, Sarah H. Yoon, Edward R. Schenk and Julie B. Baldizar Open-File Report 2007-1198 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia 2007 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Rybicki, N.B., Yoon, S.H., Schenk, E.R., and Baldizar, J.B., 2007, The Distribution of Submersed Aquatic Vegetation in the Fresh and Oligohaline Tidal Potomac River, 2004, U.S. Geological Survey, Reston VA, Open-Fi1e Report 2007-1198, 27 pgs. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. ii Contents Introduction ....................................................................................................................................................1 Methods………………………………………………………………………………………………….…..1 Results……………………………………………………………………………………………………….3 Upper tidal Potomac River………………………………………………………………………..............3 Lower tidal Potomac River……………………………………………………………………………..…4 Upper oligohaline Potomac River estuary………………………………………………………………...4 References ......................................................................................................................................................5 Figures 1. Percent cover of hydrilla in SAV beds located in the tidal Potomac River from Washington, DC to Broad Creek, MD, 2004………………………………………………………………….…6 2. Percent cover of hydrilla in SAV beds located in the tidal Potomac River from Broad Creek, MD to Chicamuxen Creek, MD, 2004……………………………..………………………………7 3. Percent cover of hydrilla in SAV beds located in the tidal Potomac River from Chopawamsic Creek, VA to the end of the river segment, 2004……….………………………………………….8 4. Location of each field bed in a continuous shoreline survey of Washington, DC, 2004……………….9 5. Location of each field bed in a continuous shoreline survey from Washington, DC to Broad Creek, MD, 2004……………...………………………………………………………..………....10 6. Location of each field bed in a continuous shoreline survey from Swan Creek, MD to Gunston Cove, VA, 2004……………………………………………………………………...………..…..11 7. Location of each field bed in a continuous shoreline survey from Mason Neck, VA to Quantico Creek, VA, 2004……….…………………………………………..…………………………....…12 8. Location of each field bed in a continuous shoreline survey near Quantico, VA, and Mallows Bay, MD 2004…………………………………………….…………………………………………..13 9. Location of each field bed in a continuous shoreline survey from Wades Bay, MD to Potomac Creek, VA, 2004……………………………………………………….…………………………..14 10. Location of each field bed in a continuous shoreline survey from Aquia Creek, VA to the end of the river segment, 2004…………………………………………………………..…………….15 11. Distribution and density of submersed aquatic vegetation and the location of the Aquatic Plant Management harvest sites in the tidal Potomac River from Washington, DC to Broad Creek, MD, 2004…………………………………………………………………………..16 12. Distribution and density of submersed aquatic vegetation and the location of the Aquatic Plant Management harvest sites in the tidal Potomac River from Broad Creek, MD to Chopawamsic Creek, VA, 2004………………………………………………………..….17 iii 13. Distribution and density of submersed aquatic vegetation and the location of the Aquatic Plant Management harvest sites in the tidal Potomac River from Chopawamsic Creek, VA to the downstream extent of the study, 2004………………………………………………...…..18 14. Percent of available habitat (area less than 2m in depth) that was vegetated in each river segment (UTR, LTR, and UOE) from 1985 to 2004 .........................................................................19 15. Area occupied by submersed aquatic vegetation for each river segment (UTR, LTR, and UOE) from 1985 to 2004………………………………………………………………………………19 Tables 1. Percent canopy cover of each species and Shannon diversity index for field beds located in the tidal Potomac River, 2004.. ......................................................................................................................20 Conversion Factors Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) mile, nautical (nmi) 1.852 kilometer (km) yard (yd) 0.9144 meter (m) Area acre 4,047 square meter (m2) acre 0.4047 hectare (ha) acre 0.4047 square hectometer (hm2) acre 0.004047 square kilometer (km2) hectare 0.01 square kilometer (km2) square foot (ft2) 929 square centimeter (cm2) square foot (ft2) 0.0929 square meter (m2) square inch (in2) 6.452 square centimeter (cm2) section (640 acres or 1 square mile) 259 square hectometer (hm2) square mile (mi2) 259 hectare (ha) square mile (mi2) 2.59 square kilometer (km2) iv The Distribution of Submersed Aquatic Vegetation in the Fresh and Oligohaline Tidal Potomac River, 2004 By Nancy B. Rybicki, Sarah H. Yoon, Edward R. Schenk, and Julie B. Baldizar INTRODUCTION Submersed aquatic vegetation (SAV) is a critical component of the Potomac River ecosystem. Though SAV provides important habitat for fauna and stabilizes bottom sediment, very dense beds may restrict recreational and commercial navigation. Exotic species of SAV are managed by the Metropolitan Washington Council of Governments Potomac Aquatic Plant Management Program (PAPMP). Selected beds of exotic SAV species that limit navigation are harvested mechanically. The program began in 1986 when approximately 40 acres of plants were harvested from 18 sites (Metropolitan Washington Council of Governments 1987). Monitoring efforts are an effective means of quantifying the distribution and abundance of the exotic species, Hydrilla verticillata (hydrilla) and other SAV species. These annual surveys provide a basis for identifying large-scale changes throughout the ecosystem and allow managers to evaluate the effectiveness of resource management policies based on a reliable scientific foundation. The U.S. Geological Survey (USGS) has monitored the distribution and composition of SAV beds in the fresh and oligohaline (salinity 0.5 to 5) tidal Potomac River since 1978 using transect sampling (1978 to 1981, 1985 to 1987, and 2002) and shoreline surveys (1983 to 2004). Shoreline survey data from the tidal Potomac River are incorporated into the Virginia Institute of Marine Science (VIMS) annual report on SAV distribution in Chesapeake Bay. The VIMS report and methods are available at http://www.vims.edu/bio/sav. Additional publications concerning SAV distribution in the Potomac River can be found at http://water.usgs.gov/nrp/proj.bib/sav/wethome.htm. METHODS The study area in the Potomac River was divided into three reaches: 1) upper tidal river (UTR) from Washington, DC to Dogue Creek, VA; 2) lower tidal river (LTR) from Dogue Creek, VA to Quantico, VA; and 3) upper oligohaline estuary (UOE) from Quantico, VA to the downriver side of Maryland Point, MD (Figs. 1 to 3). Observations of species composition in SAV beds were done by boat at approximately low tide (± 2 hrs) so that plants were visible from the water surface. Surveys were conducted between August and October 2004. We identified submersed plants to species level, recorded species composition of each bed, and estimated percent cover of each species within the bed. As in previous years, USGS monitored areas downriver of the Woodrow Wilson Bridge while colleagues at the Fisheries Division of the District of Columbia Department of Health (DCDOH) examined Washington, DC waters in the tidal Anacostia and Potomac River to the Maryland border near the Woodrow Wilson Bridge (Fig. 1, Rottman 1999; Ryan 2005). The monitoring effort in 2004 consisted of a continuous survey of all shoals and observations of SAV beds within the multi-year study area (Figs. 4 to 10). SAV field beds are the isolated or contiguous SAV beds of different species composition sampled by boat. USGS personnel outlined SAV beds on 1:24,000 scale USGS quadrangle maps indicating location of all observations including unvegetated shoals (see Ruhl et al. 1998). DCDOH personnel used a global positioning system (GPS) to delineate the perimeter or length of beds and to record locations of each field bed. The SAV beds documented by the USGS and DCDOH were then entered into a geographic information system (GIS) to create maps of distribution and abundance (Figs. 1 to 10). The percent of each species, the Shannon diversity index, and the bed density for each field bed are listed in Table 1. The Shannon diversity index for each field bed is calculated as: M Diversity = -1 * Σ ((Pv/100) * ln (Pv/100)) 1 v=1 where M represents richness (the total number of species observed) and Pv represents the proportional coverage of each species. Diversity in each bed can range from 0.00 (if one species is present) to 2.49 (if all 12 species commonly found in the Potomac are present in equal percentages). Field bed observations, classified