EVPP 550 Waterscape Ecology and Management - PowerPoint PPT Presentation

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EVPP 550 Waterscape Ecology and Management

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One of two natural lakes in Virginia. Formed when land dammed a mountain valley ... May lead to lakes or, if there are seams of carbonate, to a 'karst' landscape ... – PowerPoint PPT presentation

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Title: EVPP 550 Waterscape Ecology and Management


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 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 gtgt
    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
    Earths 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, ?
  • Ultraviolet lt 400 nm
  • Visible 400-750 nm
  • Infrared gt 750 nm
  • Light waves may also be characterized by their
    frequency, ?
  • ? c/?, 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 h? where hPlancks 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 Lakes 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
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