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

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Presentation on theme: "EVPP 550 Waterscape Ecology and Management Professor R. Christian Jones Fall 2007."— Presentation transcript:

1 EVPP 550 Waterscape 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 CaCO 3 and MgCO 3 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, z max Popular and oft-cited datum Some ecological significance –Relative depth, z r 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, T r –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: 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 m -1

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

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


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