EVPP 550 Waterscape Ecology and Management

1. EVPP 550Waterscape Ecology and Management Professor R. Christian Jones Fall 2007

2. Origins of Lakes • Glacial • Tectonic • Volcanic • Solution • Fluviatile • Impoundments

3. Origin of Lakes - Tectonic • Epeirogenesis or overall crustal uplifting • More complex than graben • Entire section of the crust is uplifted • Caspian Sea: formerly part of the ocean, cut off by crustal uplift • Lake Okeechobee, FL: similar origin, partially maintained by daming with plant material • Lake Titicaca, Peru

4. Origin of Lakes – Tectonic • Earthquake Lakes • Reelfoot Lake, TN-KY • Major earthquake (8 on Richter scale) • Caused surface to uplift in some areas and subside in others • Mississippi R was diverted into a subsidence region for several days forming Reelfoot Lake

5. Origin of Lakes - Tectonic • Landslide Lakes • Mountain Lake, VA • One of two natural lakes in Virginia • Formed when landslide dammed a mountain valley • The lake is estimated to be about 6,000 years old and geologists believe it must have been formed by rock slides and damming

6. Origin of Lakes - Volcanic • Crater/caldera Lakes • Lake occupies a caldera or collapsed volcanic crater/cone • If cone blows out the side like Mt. St. Helens, no basin left • Ex. Crater Lake, OR

7. Origin of Lakes – Volcanic Lakes • Lava dams • Lava flow dams an existing valley • Lake Kivu, Africa • Meromictic Lake, contains high conc of CO2 • Could cause suffocation if overturned

8. Origin of Lakes – Solution Lakes • Carbonate areas • Basin created by dissolution of removal by groundwater of CaCO3 and MgCO3 rocks • Overlying ground eventually collapses: “sinkhole” • May lead to lakes or, if there are seams of carbonate, to a “karst” landscape • Lakes of Central Florida

9. Origin of Lakes – Solution Lakes • Salt collapse basins • Underground seepage dissolves salt lenses, ground collapses and basin fills • Montezuma Well, AZ

10. Origin of Lakes – Fluviatile (river-made) • Ponding by deltas • Lake Pepin: WI-MN • Oxbow Lakes • Isolated meanders of an alluvial river • Lake Chicot, AR • Pothole Lakes • Excavated by streambed erosion • Grand Coulee Lakes, WA

11. Origin of Lakes – Animals • Humans • Intentional reservoirs • Incidental flooding of basins constructed for other purposes • Quarries • Peat diggings • Other agents • Beavers • Alligators

12. Origins of Lakes - Reservoirs • Purposes • Water supply • Human • Livestock • Irrigation • Flood control • Sediment control • Recreational • Power generation • Navigation

13. Origin of Lakes – Lake Districts • Because most of the factors responsible for lake origins or localized or regional, lakes tend to be clustered in “districts” • Glacial Lakes: MN, WI, Ontario, NY, New England • Oxbow Lakes: lower Mississippi Valley (AR, MS, LA, TN) • “English Lake District” • Even reservoirs are clustered due to favorable geology, physiography, demand

14. Morphology of Lakes • Parameters related to surface dimensions • Maximum length • Distance across water between two most separated points on shoreline • Most significant when this corresponds with direction of prevailing winds • Less clear in curved lakes • Maximum width or breadth • Greatest distance across water perpendicular to axis of maximum length

15. Morphology of Lakes • Parameters related to surface dimensions • Surface area • Can be derived from map by planimetry, weighing or counting squares • Determines the amount of solar energy entering the lake and the interface available for heat and gas exchange with the atmosphere • Mean width • Surface area/maximum length

16. Morphology of Lakes • Parameters related to surface dimensions • Shoreline length • Related to the amount of shallow water available for littoral organisms as well as the degree of interaction with adjacent terrestrial system (leaffall) • Shoreline development index, DL • Compares the lakes actual shoreline length with that of a circular lake of the same surface area • Allows comparison among lakes • High DL, elongate latkes, river impoundments • Low DL, calderas, solution basins, simple kettle lakes

17. Morphology of Lakes • Parameters requiring bathymetric or subsurface dimensions • Maximum depth, zmax • Popular and oft-cited datum • Some ecological significance • Relative depth, zr • Ratio of maximum depth to diameter of a circular lake with the same area • Provides a way of comparing large and small lakes

18. Morphology of Lakes • Volume • Total amount of water in the lake • Most easily derived from hypsographic curve • Hypsographic curve: Plot of Area vs. Depth

19. Morphology of Lakes • Volume • Hypsographic curve: Plot of Area vs. Depth • Can derive total water volume or volume of specific strata

20. Morphology of Lakes • Mean Depth, z bar • zbar = V/A • One of the most important and meaningful morphometric parameters • A general index of lake productivity • ↑ zbar  ↑ volume/area, dilution of incoming solar energy, ↑ volume unlit • ↓ zbar  ↓ volume/area, concentration of incoming solar energy, ↓ volume unlit

21. Morphology of Lakes • Deepest lakes are grabens; calderas and some glacial lakes can also be deep • Grabens have the greatest volume

22. Morphology of Lakes • Glacial scour lakes can be large, but not necessarily deep • Note that drift basins are neither large nor deep, but are very numerous

23. Morphology of Lakes • Hydraulic retention time, Tr • Average time spent by water in the lake • “residence time” • Tr = Volume/Outflow rate • Varies greatly, some lakes have no outlet • Superior 184 yrs • Tahoe 700 yrs • Some reservoirs have Tr of only a few days or even hours

24. Morphology of Lakes • Elements also have retention times • If very soluble and not biologically active (Cl), elemental retention time ≈ hydraulic retention time • If associated with particles or biologically reactive (P), elemental retention time >> hydraulic retention time

25. Light in Lakes • Sun is virtually the only source of enerby in natural aquatic habitat: photosynthesis and heat • Solar constant • Rate at which radiation arrives at edge of Earth’s atmosphere • ≈ 2 cal/cm2/min • More than half of this is lost coming through the atmosphere

26. Light in Lakes • Absorption by different chemicals in atmosphere • Water and ozone (O3) are especially important • Ozone is the most important in the UV range

27. Light in Lakes • Spectrum of light, wavelength, λ • Ultraviolet: < 400 nm • Visible: 400-750 nm • Infrared: > 750 nm • Light waves may also be characterized by their frequency, ν • ν = c/λ, where c = speed of light

28. Light in Lakes • Light may be considered to be made up as particles called photons • Energy (E) content of a photon is related to its frequency • E = hν where h=Planck’s constant • Therefore higher frequency (shorted wavelenth) radiation has more energy per photon • Light is often quantified as photon flux density • Moles/m2/sec; 1 mole of photons = 1 Einstein

29. Light in Lakes • Losses of Radiant Energy • Absorptive compounds in atmosphere • Cloud cover • Reflection at Lake’s surface

30. Light in Lakes • Scattering and Absorption • Physically different processes, but usually hard to separate • Scattering • deflection of photons by particles • Includes both side scattering and back scattering • Best measured by “turbidity” • Absorption • Conversion of photon to another form of energy • Usually heat, but sometimes chemical (ex psyn)

31. Light in Lakes • Attenuation • Disappearance of water with depth in a lake • Due to a combination of scattering and absorption • Approximated by the Beer-Bouguer Law • In a homogeneous medium a constant proportion of photons and their energy is absorbed (disappears) with each linear unit of medium

32. Light in Lakes • Attenuation • Mathematical statement of Beer-Bougher Law • I(z) = I(0) x e-kz • where • I(z) is Irradiance (light) at depth z • I(0) is Irradiance (light) at the surface minus reflection • k is the coefficient of attenuation • The rate of light attenuation for each unit of depth is e-k

33. Light in Lakes • K, the rate of light attenuation is due to • Water, kw • Not very large • Greatest for longer wavelengths (red) • Least for short wavelengths (blue) • Explains why in clear water objects have a bluish cast

34. Light in Lakes • K, the rate of light attenuation is due to • Dissolved material • Particulate material • Net result is to shift wavelength of max penetration from blue toward green as attenuation increases

35. Light in Lakes • K, the rate of light attenuation is determined by plotting ln I(z) vs z • Slope is –k, in this case -3.78 m-1

36. Light in Lakes • Light attenuation in lakes is also approximated by determining Secchi disc depth, zSD • Secchi disc depth has been shown to be related inversely to light attenuation coefficient • One equation commonly used is: • K = 1.7/zSD

37. Light in Lakes • Photic zone • Lower limit defined by 1% of surface light • Depth at which I(z)/I(0) = 0.01 • zPZ = - ln 0.01 / k • zPZ = 2.7 zSD