Watersheds and Aquatic Ecosystems

1. Watersheds and Aquatic Ecosystems Introduction to Fire Effects, RX-310 Fire Effects and Resource Management

2. Outline • Introduction • Watershed Components • Fire and Fire Regime Effects • Watershed Response to FOFE • Management Practices • Summary

3. 1. Introduction • Goals • Objectives • Definitions

4. Goals • Understand the effects of fire and fire regimes on watersheds and aquatic ecosystems • Understand how fire affects the resource management of watersheds and aquatic ecosystems • Understand how fire management practices can modify or alter watershed responses

5. Objectives • Identify and describe the physical, chemical, and biological components of watersheds and aquatic ecosystems • Identify how fire and fire regimes influence the physical, chemical, and biological properties of watersheds and aquatic ecosystems • Identify key responses used to evaluate the first order fire effectson watersheds and aquatic ecosystems • Discuss appropriate management practices for modifying first order fire effects on watersheds and aquatic ecosystems

6. Definitions Watershed – land area that captures precipitation, delivers the water to a stream channel network, and sends it on to a larger river, lake, or the ocean Aquatic Ecosystem – habitat for plants and animals that is dominated by water (springs, creeks, rivers, ponds, lakes, oceans, marshes, and wetlands)

7. Watersheds • Fill space • Nested hierarchies

8. 2. Watershed Components • Physical Watershed – water and sediment • Chemical Watershed – chemicals and nutrients • Biological Watershed – ecosystems and habitats

9. The Physical Watershed Movement of water and sediment through the landscape Hillsides Streams

10. The Hydrologic Cycle From Dunne and Leopold, 1978

11. Precipitation • Movement of water from the sky to the ground • Primarily fall as rain and snow • Both amounts and intensities are important • Results in rainsplash on the ground surface

12. Canopy Interception Precipitation Throughfall Litter Interception (evaporated back to the atmosphere) Stemflow Interception The process of vegetation interrupting the fall of precipitation onto the soil surface

13. Interception • Reduces raindrop impact, which reduces the detachment of soil particles • Large effect in small, low intensity storms • It is insignificant in very large rainstorms

14. Infiltration/Overland Flow Precipitation Overland Flow Infiltration Soil Column

15. Infiltration • The movement of water into the soil • Measured as a depth per unit time (1.5 cm/hr) • Governed by rain intensity, ground cover, and soil characteristics • Becomes percolation and groundwater flow (0.6 in/hr)

16. Overland Flow • Movement of water over the ground surface • Caused by rainfall exceeding infiltration • Caused by saturating the ground • Results in sheetflow and rill flow

17. Evapotranspiration • Movement of water from the ground to the sky • Evaporation from the surface and the soil • Transpiration from plants • Along with precipitation, controls soil moisture

18. Streamflow • Movement of water in established networks of valleys, canyons, and channels • Occurs where the groundwater table intersects the land surface • Reflects the water balance between precipitation and evapotranspiration

19. Stream Hydrograph 80 0 2 60 4 Rainfall in Millimeters (Inches) Flow Peak 6 40 8 Discharge in Cubic Meters per Second Lag Time (Feet) Storm Flow 20 Base Flow 0 2 0 4 Time in Days

20. Erosion • The movement of soil and sediment by the forces of gravity, wind, and water • Occurs when the available forces overcome the soil resistances (ground cover, soil characteristics, inertia)

21. Hillside Erosion GravityWindWater Dry ravel Rainsplash Mass movement Sheetwash Rilling

22. Stream Erosion • Delivery of water and sediment from the hillsides • Concentrated power • Vertical erosion of the stream bed • Horizontal erosion of the stream banks • Transport and temporary storage

23. Stream Transport • Dissolved load – solutes • Suspended load – fine particles • Saltation load – bounce along the stream bed • Bed load – rolled along the stream bed

24. Sediment Yield • Discharge of sediment at a watershed outlet • Combination of hillslope and stream erosion • An integrated average across all sections of the watershed

25. The Chemical Watershed Movement of chemicals and nutrients through the landscape Hillsides Streams

26. Chemicals and Nutrients • Sources • Decomposed rock material • Decaying plant and animal parts • Smoke and pollution

27. Chemicals and Nutrients OrganicInorganic Carbon Potassium Nitrogen Calcium Phosphorus Magnesium

28. Nutrient Cycling • Weathering of rock material / organic decay • Attached to soil particles • Leached by water moving through the soil • Uptake by plants then animals • Organic decay / fire

29. Nutrients in Streams • Delivery from hillsides and groundwater • Source of materials for aquatic plants • Organic decay • Dilution and flushing during large storms

30. The Biological Watershed Plants and animals on the landscape (ecosystems and habitat) Hillsides Streams

31. Ecosystems and Habitats • As watersheds cover all land area, all non- marine life dwells in a watershed • Ecosystems are the complex web of all life • Habitats are the setting for animal life • Terrestrial ecosystems on land • Aquatic ecosystems in the water

32. Terrestrial Ecosystems • Native species develop together • Macroscopic and microscopic life forms • Influx of exotic flora and fauna from human activities including fire

33. Aquatic Ecosystems • Native species develop together • Macroscopic and microscopic life forms • Aquatic species may spend their whole lives in water, may have an aquatic life stage, or may use streams for shelter and forage • Influx of exotic flora and fauna from human activities including fire

34. 3. Fire Effects and Fire Regime Effects • Fire Effects on Watersheds • Fire Regime Effects on Watershed Components

35. Fire Effects on Watersheds • Physical • Chemical • Biological

36. The Physical Watershed Movement of water and sediment through the landscape Hillsides Streams

37. The Hydrologic Cycle From Dunne and Leopold, 1978

38. The Hydrologic Cycle • More rain reaches the ground (loss of canopy and litter layer) • Soil water repellency reduces infiltration • Less transpiration with plant mortality • Overland flow greatly increases • Stream flow greatly increases

39. Stream Hydrograph 80 0 2 Post-fire 60 4 Rainfall in Millimeters (Inches) 6 40 8 Discharge in Cubic Meters per Second Pre-fire (Feet) 20 0 2 0 4 Time in Days

40. Post-fire Water Quality • Increase in temperature (remove shade) • Increase in turbidity (muddy water)

41. Post-fire Erosion • Erosion increases both on hillsides and in stream channels • All mechanisms of erosion are enhanced (wind, water, gravity) as resistances are removed • Water-driven erosion is particularly enhanced because of the extra runoff

42. Post-fire Erosion Dry Ravel

43. Post-fire Erosion Water Repellent Soils

44. Post-fire Erosion Rilling

45. Post-fire Erosion Headwater Stream Scour

46. Post-fire Erosion Small Stream Erosion

47. Post-fire Erosion Debris Flows

48. Post-fire Erosion Debris Flows

49. Post-fire Sediment Yield 40 30 20 Post-fire Sediment Yield Pre-fire Sediment Yield 10 1 10 1 2 3 4 5 6 7 8 9 Years Since Burning From Rowe et al, 1949

50. Post-fire Sediment Yield “Baseflow” vs. “Accelerated” Flow “Accelerated” Sediment Sediment Yield “Baseflow” Sediment *Fire Time From Swanson, 1981