Ecology of the Potomac Watershed

1. Ecology of the Potomac Watershed Tidal Potomac Teacher Training Workshop Summer 2008

2. What is a Watershed? • An area of land that drains to a common point • Watersheds can be large (the entire Mississippi River) or small (the part of the campus that drains into the GMU pond) • Includes both terrestrial and aquatic areas • Often cross political boundaries

3. Functions of Importance in Watersheds • Storage, Collection and Transport of Water (Hydrology) • Storage, Transformation, and Transport of Chemical (Biogeochemistry) • Energy Flow through Ecosystems • Maintenance of Terrestrial and Aquatic Biodiversity

4. Agents of Watershed Change • Natural Agents of Change • Flooding, drought, fire, windstorms, climate change, glaciers, volcanoes, earthquakes • Human Agents of Change • Flow modification, agricultural, timber harvest, urbanization, fire suppression, mining, harvesting of fish and wildlife, introduction of exotic species, accelerated climate change

5. The Hydrologic Cycle

6. Stream Ordering System • We can define where we are at in the longitudinal drainage network by determining stream orders • The rules for stream ordering are fairly simple: • Headwater streams are order 1 • Stream order increases by 1 when two stream of the same order come together.

7. Potomac Watershed • Potomac is a subwatershed of the Chesapeake Bay • The second largest

8. Potomac Watershed • Length: 383 miles (616 km) • Area: 14,679 mi2 • 4 states and DC • 17 counties and 9 cities in VA • 9 counties in MD • 8 counties in WVa • 5 counties in Pa

9. Potomac Watershed • Virginia has the largest area and the most people • Maryland is second in area and people • DC has the lowest area, but the highest density of people • West Virginia and Pennsylvania are largely rural

10. Potomac Watershed • Human population is concentrated in the lower middle section of the Potomac near the fall line • Above that is an area of intensive farming and beyond that forests are dominant

11. Potomac Watershed • The watershed has 4 major physiographic (terrain) provinces • The Coastal Plain consists of unconsolidated rocks (marine deposits that have never been compressed into rock) • The boundary between the Coastal Plain and the Piedmont is called the Fall Line

12. Potomac Watershed • The Piedmont consists of rolling hills and mainly crystalline rocks • It extends from the Fall Line to the base of the Blue Ridge • The Mason Fairfax campus is in the Piedmont • The Blue Ridge is a narrow area of uplifted crystalline rocks, remnant of an ancient mountain range • Shenandoah National Park is located on the Blue Ridge

13. Potomac Watershed • The Valley and Ridge Province contains the greatest portion of the watershed • It consists of the Shenandoah Valley (carbonate rocks) and ridges and smaller valleys (siliclastic rocks) paralleling it to the west into WVa • Interstate 81 traverses the Ridge and Valley Province • To the far west is a small piece of the Appalachian Plateaus Province, again siliclastic rocks

14. Potomac Watershed • Climatically, the Potomac Watershed is considered Human Subtropical to Humid Temperate • Temperature varies seasonally, mean from near freezing in January to about 80oF in July and August • Rainfall is fairly evenly distributed throughout the year with about 3-4 inches per month

15. Fate of Precipitation in a Watershed • Interception • Depression Storage • Infiltration • Surface Runoff • Interflow • Groundwater • Stormflow • Baseflow

16. Seasonal Water Budget Diagrams • Link climate and vegetation to runoff and hydrology • Look at Potential Evaporation (Temp. related), Precipitation, and soil moisture • Soil moisture utilization and water deficiency occur when Potential Evaporation exceeds Precipitation • Soil moisture recharge and water surplus occurs when Precipitation exceeds Potential Evaporation • Water surplus is what is available for runoff and stream and river flow which runs through the watershed

17. Seasonal Water Budget Diagrams • Water surplus is what is available for runoff and stream and river flow which runs through the watershed • While this diagram is for South Carolina, it is similar to what we would find in the Potomac Watershed, just a little cooler in the summer • Note that times of water surplus are Dec-April • So even though rainfall is evenly distributed seasonally, streamflow is not

18. Storm Hydrograph • A storm hydrograph shows the response stream discharge (Q) to a single storm • Basin lag is the time between the peak of precipitation and the peak of runoff • Stormflow/storm runoff is the surface runoff directly attributable to the storm

19. Effect of Urbanization on Storm Hydrograph • Urbanization results in less infiltration due to paved surfaces • This decreases basin lag time and increases peak discharge • The result is more high flow events including flooding

20. Watershed size influences the response time and flashiness of the hydrograph Characteristics of Stream & River Flow Large Watershed Small Watershed

21. Potomac Watershed • Interannual variation certainly occurs • Here we see 5 not really extreme years varying over a factor of 3 in average flow

22. Potomac Watershed • This graph shows the entire period of record • Flow has been as low as 500 cfs and as high as 400,000 cfs

23. Potomac Watershed • Last 10 years of flow data • Note annual pattern is generally consistent, but never exactly the same

24. Potomac Watershed • Ridge and Valley Province in WVa • The South Branch Potomac River viewed from Frenches Station Road near South Branch Depot in Hampshire County.

25. Potomac Watershed • Fall Line at Great Falls • River changes from flowing to tidal

26. Tidal Potomac River • Part of the Chesapeake Bay tidal system • Salinity zones • Tidal Freshwater (tidal river) <0.5 ppt • Oligohaline (transition zone) 0.5-6 ppt • Mesohaline (estuary) 6-14 ppt

27. Tidal Freshwater Potomac • Tidal freshwater Potomac consists of deep channel, shallower flanks, and much shallower embayments • Being a heavily urbanized area (about 4 million people), numerous sewage treatment plants discharge effluent • Note Blue Plains and Lower Potomac • Study area is Gunston Cove located about 2/3 down the tidal fresh section of the river

28. Historic Distribution of Submersed Macrophytes in the Tidal Potomac • According to maps and early papers summarized by Carter et al. (1985), submersed macrophytes occupied virtually all shallow water habitat at the turn of the 20th century • Gunston Cove was included

29. Macrophyte Distribution in 1980 • Anecdotal records indicate that by 1939, submersed macrophytes had declined strongly and disappeared from much of their original habitat • An outbreak of water chestnut (floating macrophyte) was observed in the 1940’s and in the lower tidal river, Myriophyllum spicatum invaded for a brief time • Surveys done in 1978-81 indicate only very sparse and widely scattered beds • Note no submersed macrophytes were found in Gunston Cove

30. P Loading and Cyanobacterial Blooms • Point Source P Loading to the Tidal Potomac (kg/day) • 32,200 • 7,700 • 1984 400 • Fueled by nutrient inputs from a burgeoning human population and resulting increases in P inputs, phytoplankton took over as dominant primary producers by about 1930. • By the 1960’s large blooms of cyanobacteria were present over most of the tidal freshwater Potomac River during late summer months

31. Potomac Watershed • Issues of Concern • Land Use • Urban Development • Point Sources • Nonpoint sources • Transportation impacts • Smart Growth vs Dumb Growth • Agriculture • Fertilizers and manure applications • Cattle grazing and feedlots • Stream bank erosion

32. Potomac Watershed • Issues of Concern • Exotic species • Hydrilla • Molluscs • Fish • Species Restorations • Hormone Pollution • Nutrients and Sediment • PCB’s

33. Potomac Watershed • Issues of Concern • Name some others?