Lec 11: Stream Ecology- Abiotic Features

4. Lec 11: Stream Ecology- Abiotic Features • Lentic-Lotic Comparisons -Major influences & processes • Hydrology, Morphology, & Discharge • Human Alterations & Sediments • Chemistry & Other Physical Features 1

5. Engineers study water as a commodity which can be stored, moved, or controlled as needed. Stream ecologists study water as a dynamic medium, home to communities of organisms. Hydrology (Biology vs. Engineering) 2

6. Hydrology • Spatial Variation Discharge variation & velocity resistance, impart spatial and thus habitat variation w/in streams -What does channelization do to biodiversity? • Temporal Variation Stream Types: 1. Perennial: Year-round discharge 2. Intermittent: Discharge most of the year 3. Ephemeral: Discharge during & after rainfall/snowmelt 3

7. Global Distribution of Permanent and Intermittent Streams 4

8. 5 Seasonal Discharge Variation Spring Same Location Fall

9. Seasonal Discharge Variation 7 6

10. Morphology: Definitions WC = Wetted Channel ACS = Active Channel FP = Flood Plain 7

11. Morphology: Definitions Channel Units: (must be greater than one active channel width) Riffle: - Moderate gradient, turbulent water surface - Areas of high velocity; Erosional Pool: -Low gradient, little or no surface turbulence -Areas of low velocity; Depositional Riparian Zone: Transition zone between the aquatic system and the adjacent land 8

15. Riffles and Pools Direction of flow Riffle Pool Water surface Porous bedrock Gravel Fine sediments Stream Reach = each riffle-pool sequence (or other repeatable units) 9

16. Riffles and Pools Elevation Pool Riffle Pool Riffle Pool Riffle Pool Downstream a Erosion b Erosion Point bar Thalweg, fastest velocity Riffle a’ b’ Point bar Pool Erosion b’ b a’ a a’ a Current rotation at bend Velocity contour, cross sectional at crossover, maximum in center Velocity contour, cross sectional at bend, maximum to outside 10

18. A - Cross sectional area W - Top width = distance from the water’s edge on one bank to the water’s edge on the other bank P - Wetted Perimeter = distance along stream bed and banks where they contact water R: Hydraulic Radius = the ratio of cross-sectional area to the wetted perimeter: R=A/P D: Hydraulic Depth = the ratio of cross-sectional area to top width: D=A/W Graphic on next frame Morphology: Open-Channel Hydraulics 11

19. Morphology: Open-Channel Hydraulics W A D P 12

22. Water Dynamics The following 3 terms are often misused interchangeably Flow (bad) can mean discharge or velocity Velocity is distance per unit time (m/s) Discharge is a measure of volume per unit time (ft3/s) Hydrology 13

23. Velocities are typically measured at a standard depth Mean Velocity is calculated for each vertical measure. Cross-sectional Velocities are summed and divided by N to get a mean stream velocity. Is mean or variation important for biota? Hydrology: How to Measure Discharge What factors might influence curve shape? 14

24. Q = Discharge= Volume of water passing a point per unit time Q=VA How to measure: Q= v1a1+v2a2+………vnan Morpology (&Hydrology): Discharge W * * ai * * * * * P n portions; Set intervals (e.g. 1m); Mean depth 15

28. Classification systems: Stream order 16

29. There are more small than large streams This is just an example…. How could these relationships vary with different types of watersheds? 17

30. Stream Changes with Distance From Source • decrease in current velocity • increase in temperature range • decrease in oxygen available source rock headstream boulders height above outfall gravel middle course sand mature river silt (estuary) outfall Distance from source 18

31. Effects of Watershed Alteration on Surface Hydrology 19

32. Discharge A Rain Rainfall, Discharge Undisturbed B Urbanized Discharge Time (h) Effects of Watershed Alteration on Surface Hydrology Hydrographs 20

33. 21

34. 1930 1980 The Effect of Dams on Missouri River Discharge 22

35. Sediments 23

36. Sediments 24

37. Embedded Substrate 25

38. Sediments 26

41. Sediments Fine Course Gravel, Silt Sand Sand Pebbles Erosion Transportation Sedimentation Fall Velocity 27

42. Sediments 28

43. Temperature varies more than high volume lentic systems Canopies of forested areas keep waters cooler than they would be in open areas. Prairie streams are almost always hotter than their neighboring forested counterparts. Other: Temperature 29

44. Oxygen is rarely a limiting factor for biota in streams: Turbulence and air friction usually facilitate enough diffusion to keep the oxygen at or near saturation. Heavily vegetated streams can reap oxygen from photosynthesis Oxygen can become reduced in: Very slow rivers Rivers with high organic contents (microbial respiration) tropical streams or rain forests. Other: Oxygen 30

45. Unnatural addition of organic pollutants especially feces from humans or livestock increases the “Biological Oxygen Demand” BOD which is a measure of microbial respiration (How to measure?) Civil engineers and hydrologists use BOD frequently as a measure of organic pollution and to determine if the native biota are in danger of experiencing hypoxic conditions The removal of canopies on traditionally cold water streams has reduced the oxygen concentrations and had adverse affects on cold-water, oxyphilic fish like trout. Other: Oxygen BOD Oxygen, Light, & Heat 31

46. Riparian vegetation & canopies reduce solar radiation -Influences on temperature and lower oxygen Turbidity: Reduce PAR for primary producers, visual predators & predator-prey dynamics Other: Light • Turbidity (scattering of light) is affected by • substrate type • bank erodability • overland runoff • land practices in the catchment basin • velocity • soil types • uniformity of stream channel and stream bed • roughness allows for breaks to settle suspended solids 32

47. Other: Light First Light Filter: Riparian Second “ “ : Water! 33

48. Jordan River – above inflow into Sea of Galilee

49. 34 Abiotic-Biotic Relationships