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Water, Light, and Lakes

Water, Light, and Lakes. Joe Conroy 31 March 2004. Goals. To explore the properties of water germane to Limnology To appreciate the importance of lake water in the global water economy To understand the role of light in providing energy to aquatic ecosystems

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Water, Light, and Lakes

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  1. Water, Light, and Lakes Joe Conroy 31 March 2004

  2. Goals • To explore the properties of water germane to Limnology • To appreciate the importance of lake water in the global water economy • To understand the role of light in providing energy to aquatic ecosystems Overreaching Goal: Explore Ecological Consequences of Topics

  3. Goals • To explore the properties of water germane to Limnology • To appreciate the importance of lake water in the global water economy • To understand the role of light in providing energy to aquatic ecosystems Overreaching Goal: Explore Ecological Consequences of Topics What does this mean for. . .?

  4. Properties of Water • “fulcrum of biochemical metabolism” • Chemistry and Physics = Boundary Conditions • Hydrogen Bonding • Ionic and Covalent character • What properties are important? • Specific Heat • Density • Viscosity • Surface Tension Photo Credit: M. Chaplin For more info and good pics: http://www.lsbu.ac.uk/water/

  5. Specific Heat • “Heatability” or thermal capacity • Extremely high for water • Due to H-bonding • 1.0cal g-1°C-1 for liquid water, 0.5 for ice @ 0°C • Heat of Fusion = 79.72cal g-1 • Heat of Evaporation = 540cal g-1 Einput melts ice -or- E loss forms ice

  6. Specific Heat Ecological Consequences? • Stability of aquatic environments • Temperature fluctuations occur seasonally, not daily

  7. Density • Molecular properties w/ interesting results • Vibrational energy • Bond length • Maximum Density @ 4°C • Ice has open spaces = less dense • Warmer water has greater vibrations = less dense • Density difference per degree lowering • Changes at different temperatures

  8. Density Figure 2-3, p. 12

  9. Density Figure 2-3, p. 12

  10. Density Ecological Consequences? • Work is needed to mix liquids w/ different ρ’s When is less work required to mix water? Winter? Summer? • How does density increase?

  11. Viscosity • Resistance to flow (think honey) •  w/ temperature (flows more easily) • Implications for passive organisms (plankton) • Determined by interactions w/ density, exposure area, speed  Stokes’ Law

  12. Viscosity Ecological Consequences? • Sinking rates of aquatic organisms • Succession of organisms?

  13. Surface Tension • At air-water interface, inward bonding causes water to adhere to itself = Tension

  14. Surface Tension Table 2-2, p. 13

  15. Surface Tension Ecological Consequences? • Habitat for Neuston at air-water interface

  16. Properties of Water - Bibliography • Wetzel – Chapter 2, pp. 8-14 • Class Notes – pp. 16, 20

  17. Sources of inflow Precipitation Surface water from watershed Groundwater seepage Spring Sources of outflow Drainage Seepage Evaporation Evapotranspiration Water Economy LAKE = INFLOW – OUTFLOW Closed Lake: no outlet -versus- Open Lake: outlet or seepage

  18. Water Economy Watershed = drainage basin or catchment area Lake Erie & Lake St. Clair Watersheds Photo Credit: Dr. R.J. Schaetzl, MSU Geology 333

  19. Where is all the Water? Figure 4-2, p. 45

  20. Water Economy Ecological Consequences? • Lake/River water = 0.017% of ocean water • Lake/River water = 0.9% of ice But. . . extremely important for aquatic organisms and humans!

  21. Aside: Storage vs. Turnover • Important concepts to distinguish • Components that store more turnover slowly • Ocean (water) • Fish (biomass) • Components that store less turnover rapidly • Atmosphere (water) • Plankton (biomass)

  22. Water Economy - Bibliography • Wetzel – Chapter 4, pp. 43-48

  23. Light in Lakes Light = Solar Radiation = Energy (Heat) • Lake optical properties affect light penetration • Properties of Energy • Can do work • Neither created or destroyed • Able to be transformed from one form to another • Radiant Energy  Potential Energy through biochemical pathways of organisms

  24. Electromagnetic Spectrum • Sun’s radiation is of various wavelengths Figure 5-1, p. 50

  25. Energy and Wavelength • Where: h = Plank’s constant (6.63x10-34J s) c = speed of light (3x108 m s-1) λ = wavelength of light ν = frequency of light •  wavelength  frequency  E •  wavelength  frequency  E

  26. Net Radiation • Not all of the sun’s radiation hits lake surfaces • 17% absorbed by the atmosphere • Ozone, water vapor, CO2, O2 • Light impinging on lakes • Depends on latitude and season • 5-10% reflected back from the lake surface • 5% scattered once it penetrates a lake • Refraction creates a longer light path length in lakes • Equation on Wetzel, p. 56

  27. Light Attenuation and Absorption • Attenuation = decrease of radiant energy with depth by both scattering and absorption • Absorption = decrease of light energy with depth due to transformation to heat • Important in lakes b/c light at depth determines E input

  28. Measuring Light in Lakes • Percent Transmission • Compares light at depth to light at surface • %Transmission = 100 * ((I0 – Iz)/I0) where: I0 = surface light Iz = light at depth z • Intensity of Radiation at depth • Exponential decrease in light intensity Iz = I0*e-ηz where: η = extinction coefficient z = depth

  29. Extinction Coefficient • Measures how quickly light is attenuated • Composite of factors: ηt = ηw + ηp + ηc where: ηt = total extinction coefficient ηw = water extinction coefficient ηp = particulate extinction coefficient ηc = colored compounds extinction coeff.

  30. Absorption and Extinction Coefficients Table 5-2, p. 57

  31. Absorption and Extinction Coefficients Figure 5-10, p. 60

  32. Special Light Measures • Photosynthetically Active Radiation (PAR) • Portion of the EM spectrum available for Ps • Approximately 400-700nm • Measured using a PAR meter • Compensation Depth • Water depth at which photosynthesis and respiration are just balanced • Approximately 1% Surface Light • Measured using a PAR meter or Secchi Disk

  33. Light Penetration, Secchi Depth, and Productivity Secchi Disk

  34. Light Penetration, Secchi Depth, and Productivity Figure 5-11, p. 61

  35. Light Penetration, Secchi Depth, and Productivity Figure 5-17, p. 66

  36. Light and Lakes Ecological Consequences? • Light provides most energy to lakes • Lake position (globally), watershed, and geology impact biota

  37. Light and Lakes - Bibliography • Wetzel – Chapter 5, pp. 49-69 • Class Notes – pp. 16, 20-23

  38. QUESTIONS?

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