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 

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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. 

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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
iv

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) 
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 Pvrepresents 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 by the percent cover of Hydrilla 

verticillata, are shown in figures 1 to 3. 

SAV beds shown in figures 11, 12, and 13 were delineated by VIMS based on 

aerial photographs, then digitized and classified for ground cover density. Density was 

determined using the Crown Density Scale adapted from Paine (1981). Bed densities 

range from one to four with one corresponding to less than 10% vegetation coverage, two 

representing between 10 and 40% coverage, three representing between 41 and 70% 

coverage and four corresponding to 71 to 100% coverage. The area and density of each 

photo-interpreted (PI) bed was determined by VIMS. The VIMS delineation process 

resulted in bed area outlines to which we have added corresponding field data on species 

composition. However, the VIMS SAV coverage data did not include field beds below 

their detection limit (approximately 5 m2

). 

The percent of each species in the three river reaches of the continuous shoreline 

survey is summarized in the results section. The area of each species is computed based 

on a weighted-average formula. During the shoreline survey, we made field observations 

of species composition within a VIMS PI bed. Using GIS software, we aligned each of 

the field beds with the PI beds to determine the area of each field bed and subsequently to 

calculate the coverage by species in each PI bed where species data were available. If 

more than one field observation was made in a PI bed, we sub-divided the PI bed area 

according to the relative size of each field bed and averaged species data proportionally 

to determine the percentage of each species in a PI bed and in the cumulative area of the 

study in each river reach (Rybicki 2000, Rybicki and Landwehr, 2007). 

2 
RESULTS 

SAV coverage increased in all three river reaches between 2003 and 2004 (Figs. 

14 and 15). Hydrilla dominated many of the field beds (Fig. 1 to 3). The shoreline 

survey included 170 observations of field beds of various sizes (12 m2 to approximately 

236 ha) and density (Table 1). The species and percent cover data shown in Table 1 

correspond to field bed locations shown in Figs. 4 to 10. Several of the harvest sites in 

the UTR, LTR, and UOE had SAV densities of 70 to 100 % cover (Fig. 11 to 13) and the 

beds were comprised of exotic species (Table 1; Figs. 1 to 3). Of the nine species 

observed in the Potomac River in 2004, three are exotic (hydrilla, Myriophyllum spicatum

[milfoil], Najas minor [naiad]). Hydrilla dominated (> 40 % of the coverage) the UTR 

and the LTR, and milfoil dominated the UOE. Naiad coverage was minimal (< 1 %) in 

the UTR and UOE but was 7 % of the LTR SAV coverage. Two native species, 

Vallisneria americana (wild celery) and Ceratophyllum demersum (coontail) were 

abundant but did not dominate any river segment. Wild celery comprised 15 % of the 

UTR, 19 % of the LTR, and only 1 % of the UOE SAV coverage. Coontail coverage was 

10 % of the UTR and LTR, but only 2% of the UOE SAV coverage. Some species were 

relatively rare, namely the macroalga Chara vulgaris (muskgrass), Najas quadalupensis

(southern naiad), Elodea canadensis (waterweed), and Heteranthera dubia (stargrass)). 

In 2004, precipitation and river flow were above average, yet the total SAV coverage 

increased. 

UPPER TIDAL POTOMAC RIVER (UTR)

 

In the UTR, we found the following seven SAV species, in order from most to 

least abundant: 65 % hydrilla, 15 % wild celery, 10 % milfoil, 10 % coontail, <1 % naiad 

or southern naiad, and traces of muskgrass. Compared to 2003, hydrilla, coontail, and 

wild celery coverage increased substantially in this region. 

In Washington, DC, SAV coverage fell sharply in 2003 but recovered somewhat 

in 2004. VIMS photo-interpretation did not register a single bed in 2004 (Fig. 11) and 

field observations revealed only 18 beds (Fig. 1): all less than 70 % cover (Table 1). The 

few beds that were present were typically single-species beds and contained either 

hydrilla or wild celery (Figs. 1 and 4; Table 1). 

For the second year in a row, large, dense beds were absent in the middle of the 

Potomac River around the Woodrow Wilson Bridge and at the mouth of Hunting Creek 

(Figs. 5 and 11). Vegetation was patchy and consisted mostly of hydrilla along the 

Virginia side of the Potomac River downstream of Hunting Creek (Figs. 1, 2, 11, and 12). 

Many beds on the mainstem of the Potomac were dominated by wild celery or 

milfoil, whereas hydrilla alone dominated beds within Broad, Piscataway, and Dogue 

Creeks (Figs. 2 and 6; Table 1). A substantial bed at the mouth of Dogue Creek 

contained 80 % wild celery (Figs. 2 and 6). Wild celery also was the dominant species in 

beds in the main stem of the Potomac River downstream of Dogue Creek to the end of 

the UTR reach (Figs. 2 and 6). 

3 
Swan Creek supported one of the few populations of muskgrass in the study area. 

Muskgrass was present in several beds opposite Broad Creek. Coontail rarely dominated 

field beds except in one site along Swan Creek. Southern naiad was present in Dogue 

Creek and in the mouth of Little Hunting Creek. 

 

LOWER TIDAL POTOMAC RIVER (LTR) 

In the LTR we found seven SAV species: 49 % hydrilla, 19 % wild celery, 15 % 

milfoil, 10 % coontail, 7 % naiad, and <1 % southern naiad or muskgrass. Wild celery, 

coontail, and naiad coverage increased between 2003 and 2004 at the expense of hydrilla 

and milfoil. In contrast to 2003, muskgrass was present and stargrass was absent in 2004. 

Wild celery was dominant along the upstream shore of Gunston Cove whereas 

hydrilla was abundant in the large, innermost beds (Figs. 2 and 6; Table 1). The narrow, 

fringing beds on the downstream shore of Gunston Cove were dominated by milfoil. In 

2003 milfoil dominated, but in 2004, wildcelery dominated the Maryland side of the 

Potomac, across from Gunston Cove and south to Pomonkey Creek (Figs. 2 and 6; Table 

1). 

The vegetation around Mason Neck and in Pomonkey Creek was primarily wild 

celery (Figs. 2, 6) as it was in 2003. SAV was sparse at Indian Head and between 

Pomonkey Creek and Mattawoman Creek, and consisted mainly of milfoil. Little change 

in species composition was observed between 2003 and 2004 (Figs. 2 and 7; Table 1). 

The majority of shoals in Mattawoman Creek were vegetated in 2004, as in 2003 

(Fig. 12). At the mouth of the creek, milfoil and wild celery were abundant, although 

dominance by hydrilla was noted for most beds further upstream (Figs. 2 and 7; Table 1). 

Southern naid and coontail dominated several beds in this creek. 

Chicamuxen Creek was densely vegetated in 2004, as in most years, and 

contained large amounts of milfoil (Figs. 2, 8, and 12; Table 1). Chicamuxen Creek had 

some of the more diverse beds in 2004 and included southern naiad and muskgrass; two 

of the rarest species in the three study reaches. 

Hydrilla was the most abundant species in the Occoquan River and naiad 

dominated Belmont Bay (Figs. 2 and 7; Table 1). Hydrilla also was the dominant species 

in beds at the mouth of Neabsco Creek and in Powells Creek (Figs. 2 and 7). Wild celery 

was the dominant SAV in outer beds and hydrilla dominated inner, nearshore beds in the 

Potomac River upstream of Quantico Creek (Fig. 7). Hydrilla was dominant in Quantico 

Creek. 

UPPER OLIGOHALINE POTOMAC RIVER ESTUARY (UOE) 

Seven SAV species were present in 2004 in this reach with the following 

composition: 63 % milfoil, 32 % hydrilla, 1 % wild celery, 2 % coontail, < 1 % naiad, 

and a trace of waterweed and stargrass. The percentage of milfoil has increased 

substantially in recent years in this river segment. In contrast to 2003, waterweed and 

stargrass were present in 2004 and southern naiad was absent. 

Milfoil was dominant on the Maryland side of the Potomac, present within 4 km 

of the upstream boundary of the UOE and in the bay north of Wades Bay (Figs. 3 and 8; 

4 
5 

Table 1). Milfoil and wild celery were common in Wades Bay (Figs. 3, 8, 9, and 10; 

Table 1) whereas hydrilla dominated the Mallows Bay bed (Figs. 3 and 8). 

Hydrilla was the most abundant species in the cove just south of Quantico, VA. 

South from Quantico, for approximately 6 km, beds of hydrilla and milfoil were equally 

abundant or alternated dominance. Milfoil dominated the Virginia shoreline for the 6 km 

north of the mouth of Aquia Creek (Figs. 3, 8, and 9). Within Aquia Creek, hydrilla or 

milfoil were the dominant species (Figs. 3 and 9; Table 1). 

Between Aquia and Potomac Creeks, and in the mouth of Potomac Creek, milfoil 

was common and there were small amounts of hydrilla, coontail, and naiad (Figs. 3, 9, 

10; Table 1). In the upper portion of Potomac Creek, hydrilla was the lone species in 

2004 (Fig. 10). 

REFERENCES 

Metropolitan Washington Council of Governments. 1987. Potomac SAV news, no. 2 

Summer 1987. 

Paine, D.P. 1981. Aerial photography and image interpretation for resource 

management. John Wiley and Sons, Inc., New York City, NY. 571 pp. 

Rottman, A. 1999. Aquatic Vegetation Monitoring 1998. Submitted to U.S. Fish and 

Wildlife Service for the Fisheries and Wildlife Division of the Government of the 

District of Columbia. Report F-2-8-13. 

Ruhl H.A., Rybicki N.B., Reel J.T., and Carter V. 1999. Distribution and abundance of 

submersed aquatic vegetation in the tidal Potomac River and upper Potomac 

Estuary, Maryland, Virginia, and the District of Columbia, 1993-1998 (U. S. 

Geological Survey Open-File Report 99-233). 

Rybicki N.B. 2000. Relationships between environmental variables and submersed 

aquatic vegetation in the Potomac River, 1985-1997 (Ph. D Thesis, George Mason 

University, Fairfax, VA). 

Rybicki, N. B., and Landwehr, J.M. 2007. Long-term changes in abundance and 

diversity of macrophyte and waterfowl populations in an estuary with exotic 

macrophytes and improving water quality, Limnology and Oceanography, 52(3): 

p. 1195-1207. 

 

Ryan, D. 2005. 2004 submerged aquatic vegetation survey of the Potomac and Anacostia 

Rivers within the District of Columbia. Submitted to U.S. Fish and Wildlife 

Service for the Fisheries and Wildlife Division of the Government of the District 

of Columbia. Report F-2-8-19. 
Figure 1 Percent cover of hydrilla in SAV beds located in the tidal Potomac River from Washington, DC to 

Broad Creek, MD, 2004. UTR is the Upper Tidal River study segment. 

6
Figure 2 Percent cover of hydrilla in SAV beds located in the tidal Potomac River from Broad Creek, MD to Chicamuxen Cre

Study segments are the Upper Tidal River (UTR), Lower Tidal River (LTR), and Upper Oligohaline Estuary (UOE). 

7
Figure 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. UOE is the Upper Oligohaline Estuary study segment. 

8
Figure 4 Location of each field bed in a continuous shoreline survey of Washington, DC, 2004. UTR is the Upper Tidal River 

9
Figure 5 Location of each field bed in a continuous shoreline survey from Washington, DC to Broad Creek, MD, 2004. 

10
Figure 6 Location of each field bed in a continuous shoreline survey from Swan Creek, MD to Gunston Cove, VA, 2004. 

River segments are the Upper Tidal River (UTR) and Lower Tidal River (LTR). 

11
Figure 7 Location of each field bed in a continuous shoreline survey from Mason Neck, VA to Quantico Creek, VA, 2004. 

12
LTR

UOE

Figure 8 Location of each field bed in a continuous shoreline survey near Quantico, VA and Mallows Bay, MD, 2004. 

River segments are the Lower Tidal River (LTR) and Upper Oligohaline Estuary (UOE). 

13
Figure 9 Location of each field bed in a continuous shoreline survey from Wades Bay, MD to Potomac Creek, VA, 2004. 

14
Figure 10 Location of each field bed in a continuous shoreline survey from Aquia Creek, VA to the end of the river segment, 20

UOE is the Upper Oligohaline Estuary river segment. 

15
Figure 11 Distribution and density of submersed aquatic vegetation and the locations of the Aquatic Plant Management harvest 

Potomac River from Washington, DC to Broad Creek, MD, 2004. UTR is the Upper Tidal River study segment. 

16
Figure 12 Distribution and density of submersed aquatic vegetation and the locations of the Aquatic Plant Management harvest 

River from Broad Creek, MD to Chopawamsic Creek, VA, 2004. The river segments are the Upper Tidal River (UTR(LTR), and the Upper Oligohaline Estuary (UOE). 

17
18

Figure 13 Distribution and density of submersed aquatic vegetation and the locations of the Aquatic Plant Management harvest 

River from Chopawamsic Creek, VA to the downstream extent of the study, 2004. UOE is the Upper Oligohaline Es
0

10

20

30

40

50

60

19851986198719881989199019911992199319941995199619971998199920002001200220032004

Year

Pecent of available habitat with SAV

UTR LTR UOE

Figure 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. The UTR, LTR, and UOE have 

2956, 5173, and 3,355 hectares of available habitat, respectively. 

0

200

400

600

800

1000

1200

1400

1600

1800

19851986198719881989199019911992199319941995199619971998199920002001200220032004

Year

SAV area (ha)

UTR LTR UOE

Figure 15 Area occupied by submersed aquatic vegetation (SAV) for each river segment (UTR, 

LTR, and UOE) from 1985 to 2004. SAV area from Virginia Institute of Marine Science 

(http://www.vims.edu/bio/sav/historical.html) except from US Geological Survey in 1988 

(Rybicki and Landwehr, 2007). 

19 
Table 1. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the shoreline in th

2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Braun-Blanquet c1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed is abbreviated as: P_H(milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (common waterwee

(muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD 

8/10/2004 1 USGS Ft. Belvoir 4 100 0 0 0 0 0 0 8/10/2004 2 USGS Ft. Belvoir 3 99 1 0 0 0 0 0 

8/10/2004 3 USGS Ft. Belvoir 3 100 0 0 0 0 0 0 

8/10/2004 4 USGS Ft. Belvoir 4 99 0 0 1 0 0 0 

8/10/2004 5 USGS Ft. Belvoir 3 99 0 0 1 0 0 0 

8/10/2004 6 USGS Ft. Belvoir 1 100 0 0 0 0 0 0 

8/10/2004 7 USGS Ft. Belvoir 3 45 50 5 0 0 0 0 

8/10/2004 8 USGS Ft. Belvoir 1 25 75 0 0 0 0 0 

8/10/2004 9 USGS Ft. Belvoir 4 0 0 100 0 0 0 0 

8/10/2004 10 USGS Ft. Belvoir 4 5 0 40 10 45 0 0 

8/10/2004 11 USGS Ft. Belvoir 4 0 0 75 0 25 0 0 

8/16/2004 12 USGS Quantico 3 0 0 95 0 5 0 0 

8/16/2004 13 USGS Indian Head 3 40 19 40 0 1 0 0 

8/16/2004 14 USGS Indian Head 4 0 100 0 0 0 0 0 

8/16/2004 15 USGS Indian Head 4 45 5 5 15 20 5 0 

8/16/2004 16 USGS Indian Head 4 3 60 0 35 3 0 0 8/16/2004 17 USGS Indian Head 4 34 5 0 30 31 0 0 8/16/2004 18 USGS Indian Head 3 10 0 90 0 0 0 0 

8/16/2004 19 USGS Indian Head 2 0 40 60 0 0 0 0 

8/16/2004 20 USGS Indian Head 4 10 20 70 0 0 0 0 

8/16/2004 21 USGS Indian Head 1 0 0 100 0 0 0 0 

8/16/2004 22 USGS Indian Head 1 0 100 0 0 0 0 0 

8/16/2004 23 USGS Indian Head 1 15 75 10 0 0 0 0 

20 
Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Bcover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD 

8/16/2004 24 USGS Indian Head 2 0 50 50 0 0 0 0 

9/8/2004 25 USGS Indian Head 4 99 0 0 1 0 0 0 

9/8/2004 26 USGS Indian Head 4 75 0 20 3 3 0 0 

9/8/2004 27 USGS Indian Head 4 90 0 0 3 8 0 0 

9/8/2004 28 USGS Indian Head 3 95 0 0 5 0 0 0 9/8/2004 29 USGS Indian Head 4 70 3 3 3 23 0 0 

9/8/2004 30 USGS Indian Head 4 30 0 0 70 0 0 0 

9/24/2004 32 USGS Widewater 4 99 1 0 0 0 0 0 

9/24/2004 33 USGS Widewater 3 97 2 0 1 0 0 0 

9/24/2004 34 USGS Widewater 3 1 99 0 0 0 0 0 

9/24/2004 35 USGS Widewater 4 25 70 5 0 0 0 0 

9/24/2004 36 USGS Widewater 4 43 50 1 1 5 0 1 

9/24/2004 37 USGS Widewater 4 40 57 0 2 1 0 0 

9/24/2004 38 USGS Widewater 4 10 89 1 1 1 0 0 

9/24/2004 39 USGS Widewater 4 20 80 0 0 0 0 0 

9/24/2004 40 USGS Widewater 4 98 2 0 0 0 0 0 

9/24/2004 41 USGS Widewater 4 1 99 0 0 0 0 0 

9/24/2004 42 USGS Widewater 3 0 100 0 0 0 0 0 

10/12/2004 43 USGS Widewater 2 30 70 0 0 0 0 0 

10/12/2004 44 USGS Widewater 2 0 0 40 60 0 0 0 

10/12/2004 45 USGS Widewater 2 30 65 0 5 0 0 0 

10/12/2004 46 USGS Widewater 3 60 30 0 10 0 0 0 

21 
Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Bcover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD 

10/12/2004 47 USGS Widewater 2 0 99 0 0 0 0 0 10/12/2004 48 USGS Widewater 4 0 100 0 0 0 0 0 

10/12/2004 49 USGS Widewater 3 0 100 0 0 0 0 0 

10/12/2004 50 USGS Widewater 2 0 65 30 0 0 0 0 

10/12/2004 51 USGS Widewater 4 0 50 50 0 0 0 0 

10/12/2004 52 USGS Widewater 3 0 40 60 0 0 0 0 

10/12/2004 53 USGS Widewater 3 0 5 95 0 0 0 0 

10/14/2004 54 USGS Indian Head 4 70 1 2 25 2 0 0 

10/14/2004 55 USGS Indian Head 3 0 0 95 5 0 0 0 

10/14/2004 56 USGS Indian Head 4 25 1 3 70 1 0 0 

10/14/2004 57 USGS Indian Head 4 95 5 0 0 0 0 0 

10/14/2004 58 USGS Indian Head 2 0 10 90 0 0 0 0 

10/14/2004 59 USGS Indian Head 3 0 70 30 0 0 0 0 

10/14/2004 60 USGS Indian Head 4 0 100 0 0 0 0 0 

10/14/2004 61 USGS Indian Head 2 0 60 40 0 0 0 0 

10/14/2004 62 USGS Indian Head 3 0 20 80 0 0 0 0 

10/14/2004 63 USGS Indian Head 4 30 40 5 15 10 0 0 

10/20/2004 64 USGS Passapatanzy 2 0 100 0 0 0 0 0 

10/20/2004 65 USGS Passapatanzy 3 0 100 0 0 0 0 0 

10/20/2004 66 USGS Passapatanzy 1 0 95 0 5 0 0 0 

10/20/2004 67 USGS Passapatanzy 2 35 0 0 35 30 0 0 

22 
Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Bcover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD 

10/20/2004 68 USGS Passapatanzy 3 100 0 0 0 0 0 0 10/20/2004 69 USGS Passapatanzy 1 100 0 0 0 0 0 0 

10/21/2004 70 USGS Mt. Vernon 4 10 0 80 10 0 0 0 

10/21/2004 71 USGS Mt. Vernon 4 40 30 0 30 0 0 0 

10/21/2004 72 USGS Mt. Vernon 3 60 0 0 40 0 0 0 10/21/2004 73 USGS Mt. Vernon 4 60 20 0 20 0 0 0 

10/21/2004 74 USGS Mt. Vernon 4 95 0 0 5 0 0 0 10/21/2004 75 USGS Mt. Vernon 4 65 0 0 35 0 0 0 10/21/2004 76 USGS Mt. Vernon 4 50 30 0 20 0 0 0 

10/21/2004 77 USGS Mt. Vernon 4 5 0 95 0 0 0 0 

10/21/2004 78 USGS Mt. Vernon 4 60 30 0 10 0 0 0 

10/21/2004 79 USGS Mt. Vernon 3 0 0 100 0 0 0 0 

10/21/2004 80 USGS Mt. Vernon 2 50 50 0 0 0 0 0 

10/21/2004 81 USGS Mt. Vernon 2 30 40 20 10 0 0 0 

10/21/2004 82 USGS Mt. Vernon 3 40 0 60 0 0 0 0 10/21/2004 83 USGS Mt. Vernon 4 25 5 60 10 0 0 0 

10/21/2004 84 USGS Mt. Vernon 2 80 0 0 20 0 0 0 

10/21/2004 85 USGS Mt. Vernon 3 0 0 100 0 0 0 0 

10/21/2004 86 USGS Port Tobacco 3 0 0 100 0 0 0 0 

10/22/2004 87 USGS Mt. Vernon 3 0 15 85 0 0 0 0 

10/22/2004 88 USGS Mt. Vernon 3 20 60 10 10 0 0 0 10/22/2004 89 USGS Mt. Vernon 4 10 0 0 90 0 0 0 10/22/2004 90 USGS Mt. Vernon 2 5 0 90 5 0 0 0 

23 
Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Bcover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD P_

10/22/2004 91 USGS Mt. Vernon 3 0 15 85 0 0 0 0 10/22/2004 92 USGS Mt. Vernon 2 0 100 0 0 0 0 0 

10/22/2004 93 USGS Mt. Vernon 3 0 0 100 0 0 0 0 

10/22/2004 94 USGS Mt. Vernon 2 60 0 40 0 0 0 0 

10/22/2004 95 USGS Mt. Vernon 4 100 0 0 0 0 0 0 

10/22/2004 96 USGS Alexandria 4 100 0 0 0 0 0 0 

10/25/2004 97 USGS Quantico 2 100 0 0 0 0 0 0 10/25/2004 98 USGS Quantico 1 100 0 0 0 0 0 0 10/25/2004 99 USGS Quantico 1 0 0 100 0 0 0 0 

10/25/2004 100 USGS Quantico 2 100 0 0 0 0 0 0 

10/25/2004 101 USGS Quantico 3 95 0 0 5 0 0 0 

10/25/2004 102 USGS Quantico 4 16 0 80 2 2 0 0 

10/25/2004 103 USGS Quantico 1 0 0 100 0 0 0 0 

10/25/2004 104 USGS Quantico 4 92 2 2 2 2 0 0 

10/25/2004 105 USGS Quantico 2 0 0 100 0 0 0 0 

10/25/2004 106 USGS Quantico 4 85 10 0 3 2 0 0 

10/25/2004 107 USGS Quantico 4 0 0 100 0 0 0 0 

10/25/2004 108 USGS Quantico 4 96 0 0 2 2 0 0 

10/25/2004 109 USGS Quantico 4 70 0 0 2 28 0 0 

10/25/2004 110 USGS Quantico 4 98 0 0 1 1 0 0 

10/25/2004 111 USGS Quantico 4 60 0 5 30 5 0 0 

10/25/2004 112 USGS Quantico 4 80 5 5 10 0 0 0 

Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a B

24 
cover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i

(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD 

10/25/2004 113 USGS Quantico 4 0 0 100 0 0 0 0 10/25/2004 114 USGS Quantico 4 90 5 0 5 0 0 0 

10/25/2004 115 USGS Quantico 1 40 29 30 1 0 0 0 

10/25/2004 116 USGS Quantico 4 60 10 0 25 5 0 0 10/25/2004 117 USGS Quantico 2 0 100 0 0 0 0 0 10/25/2004 118 USGS Ft. Belvoir 4 99 0 0 0 1 0 0 

10/26/2004 119 USGS Ft. Belvoir 3 0 0 100 0 0 0 0 

10/26/2004 120 USGS Mt. Vernon 3 0 0 100 0 0 0 0 10/26/2004 121 USGS Mt. Vernon 4 90 0 0 6 2 2 0 

10/26/2004 122 USGS Mt. Vernon 1 0 0 100 0 0 0 0 

10/26/2004 123 USGS Ft. Belvoir 4 90 0 0 6 2 2 0 

10/26/2004 124 USGS Mt. Vernon 4 70 1 20 5 4 0 0 10/26/2004 125 USGS Mt. Vernon 4 5 10 80 5 0 0 0 

10/26/2004 126 USGS Mt. Vernon 2 85 10 0 3 0 2 0 10/26/2004 127 USGS Mt. Vernon 1 0 100 0 0 0 0 0 

10/26/2004 128 USGS Mt. Vernon 4 5 5 90 0 0 0 0 

10/26/2004 129 USGS Mt. Vernon 2 20 60 20 0 0 0 0 

10/26/2004 130 USGS Mt. Vernon 3 10 10 75 5 0 0 0 

10/26/2004 131 USGS Mt. Vernon 4 25 50 0 25 0 0 0 

10/26/2004 132 USGS Mt. Vernon 4 20 0 80 0 0 0 0 10/26/2004 133 USGS Mt. Vernon 4 60 0 0 40 0 0 0 10/26/2004 134 USGS Alexandria 4 75 0 15 10 0 0 0 10/26/2004 135 USGS Alexandria 2 80 0 0 0 20 0 0 

Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Bcover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i

25 
(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source USGS quad Density class P_HV P_MS P_VA P_CD P_NM P_NGU P_HD P

10/27/2004 136 USGS Ft. Belvoir 1 0 100 0 0 0 0 0 10/27/2004 137 USGS Ft. Belvoir 2 0 30 50 20 0 0 0 10/27/2004 138 USGS Ft. Belvoir 2 5 0 95 0 0 0 0 10/27/2004 139 USGS Ft. Belvoir 4 90 5 5 0 0 0 0 10/27/2004 140 USGS Ft. Belvoir 4 0 5 95 0 0 0 0 10/27/2004 141 USGS Ft. Belvoir 4 0 40 60 0 0 0 0 10/27/2004 142 USGS Ft. Belvoir 4 30 0 0 0 70 0 0 10/14/2004 143 USGS Mattawoman Cr. 3 50 0 20 30 0 0 0 10/14/2004 144 USGS Mattawoman Cr. 2 0 0 90 10 0 0 0 10/14/2004 145 USGS Mattawoman Cr. 3 90 0 0 10 0 0 0 10/14/2004 146 USGS Mattawoman Cr. 4 0 0 95 5 0 0 0 10/14/2004 147 USGS Mattawoman Cr. 2 80 0 0 10 5 5 0 10/14/2004 148 USGS Mattawoman Cr. 1 0 0 100 0 0 0 0 10/14/2004 149 USGS Mattawoman Cr. 3 95 5 0 0 0 0 0 10/14/2004 150 USGS Mattawoman Cr. 3 0 100 0 0 0 0 0 10/14/2004 151 USGS Mattawoman Cr. 1 10 0 90 0 0 0 0 10/14/2004 152 USGS Mattawoman Cr. 3 0 10 90 0 0 0 0 

9/23/2004 153 DOH Alexandria 1 100 0 0 0 0 0 0 

9/23/2004 154 DOH Alexandria 3 99 0 0 1 0 0 0 

9/23/2004 155 DOH Washington West 1 100 0 0 0 0 0 0 

9/23/2004 156 DOH Washington West 1 100 0 0 0 0 0 0 9/23/2004 157 DOH Washington West 1 100 0 0 0 0 0 0 9/24/2004 158 DOH Alexandria 1 100 0 0 0 0 0 0 

Table 1 – continued. Percent canopy cover of each species and Shannon diversity index for field beds located continuously along the sh

Potomac River, 2004. Field bed numbers correspond to the numbers in Figs. 4 to 10. Density classes are USGS field data based on a Bcover model where: 1 = 1 to 10 %, 2 = 11 to 40 %, 3 = 41 to 70 %, and 4 = 71 to 100 % cover. Percent cover of each species in a bed i

26 
27 

(hydrilla), P_MS (milfoil), P_VA (wild celery), P_CD (coontail), P_NM (naiad), P_NGU (southern naiad), P_HD (stargrass), P_EC (co

P_CV (muskgrass). USGS is U.S. Geological Survey and DOH is DC Dept. of Health. 

Survey 

date 

Field 

bed 

number 

Data 

source 

USGS quad Density 

class 

P_HV P_MS P_VA P_CD P_NM P_NGU P_HD P

9/24/2004 159 DOH Alexandria 1 0 0 100 0 0 0 0 9/24/2004 160 DOH Alexandria 2 0 0 100 0 0 0 0 9/24/2004 161 DOH Alexandria 2 0 0 100 0 0 0 0 9/24/2004 162 DOH Washington West 2 0 0 100 0 0 0 0 

9/24/2004 163 DOH Washington West 3 100 0 0 0 0 0 0 9/24/2004 164 DOH Washington West 1 100 0 0 0 0 0 0 9/27/2004 165 DOH Washington West 2 100 0 0 0 0 0 0 9/27/2004 166 DOH Washington West 1 100 0 0 0 0 0 0 9/27/2004 167 DOH Washington West 2 100 0 0 0 0 0 0 9/27/2004 168 DOH Washington West 1 100 0 0 0 0 0 0 

9/27/2004 169 DOH Washington West 1 100 0 0 0 0 0 0 

10/1/2004 170 DOH Alexandria 2 0 0 100 0 0 0 0