Chapter 4: Rivers and Lakes - Their Distribution, Origins, and Forms

Geomorphology

  • Geomorphology of lakes is tied to physical, chemical, and biological processes occurring in waterbodies

    • plays major role in controlling lake’s metabolism of surrounding terrestrial area

    • controls nature of surface and the underground influxes and out-fluxes of the lake

      • ex: the lake’s water renewal rate

Morphometry

  • Morphometry: the geography of lake basins and their catchments

  • Drainage basin, catchment, and watershed = the surrounding land area (ecosystem) draining into a waterbody

  • Lakes always drain downhill because they are affected by everything being brought down by gravity

  • Basin = shape of a lake’s waterbody

    • influences lake’s productivity

    • ex: steep-sided U-shaped or V-shaped basins = unproductive

      • because they smaller volumes of water that are in contact with important sediments

    • ex: shallow basins with greater water % = productive

      • because they have larger volumes of water in contact with sediments

  • The highest order of drainage basins, the ocean drainage basins

    • Canada has 5 major drainage basins

      • the Arctic, Atlantic, Pacific, Hudson Bay, and Gulf of Mexico basins

  • Watershed boundries

    • What are the highest points? = how to find drainages points

    • What happens on land is critical to find out since that is what will happen to ground water in lakes

  • Lakes are downhill from land which will greatly be affected by catchment characteristics (because of gravity)

  • Descriptors of lake morphometry:

    • Length (l) - distant of 2 most distant points

    • Width (b) - maximum distance perpendicular to length

    • Surface Area (SA) - easily measured

    • Volume (V)

    • Max Depth (Zmax) - maximum depth of lake

      • important for knowing what is happening in lake

    • Mean Depth (Zmean) = V/SA

    • Relative Depth (Zr) = Zmax : Mean diameter

      • max depth relative to mean diameter

      • = ratio of the max depth (Zmax) as a % of the mean diameter of the lake at the surface

      • expressed as a %

    • Shoreline length = L

      • bigger shoreline will be different from smaller shoreline even if both have same SA

    • Shoreline development = DL =\frac{L}{2\sqrt{\pi A^{}}} = ratio or the length of a shoreline (L) to the circumference of a circle of area equal to that of the length

      • so very circular lakes (e.g. craters) approach a value of 1.0

      • most lakes have very different shapes from circles, and so they have DL > 1.0

  • Fetch: the distance a wind blows over water without interuption

    • heat + wind = more different environments

    • ex: lakes that have big islands in them will disrupt the fetch

  • depth sounders = instruments used to measure an estimate of depth

    • ex: transducer and receiver constantly measures depth and the symmetry of lakes

  • Bathymetric Maps: used to depict the underwater topography of lakes and oceans, providing critical information for navigation, resource assessment, and environmental studies

  • Physical characteristics of water bodies:

    • mixing

    • thermal stratification (different temperatures have different levels of density)

    • chemistry

    • littoral zone

    • macrophytes

  • lakes can be divided in to distinct horizontal and vertical zones

  • 3 major zones in a lake:

    • 1) Littoral zone: shallow water

      • zone of lake where rooted aquatic macrophytes can grow

        • generally angiosperms

      • offer many different habitats that will all serve different function

        • ex: on rocks, sand, mud, shallow water

    • 2) Pelagic zone: middle of lake (open water)

      • photic zone

      • where most phytoplankton and zooplankton live

    • 3) Profundal zone: deepest part of lake

      • aphotic zone

      • where benthos live

  • Periphyton: algae attached to a substrate (as opposed to phytoplankton)

    • attached in littoral zone

    • epiphytic: attached to plants (live on macrophytes)

    • epilithic: attached to rocks

    • epipsammic: attached to sand grains

      • very adaptive

      • sand is hard to live on = highly specialized organisms

    • epipelic: associated with surface sediments

  • zones defined by light penetration

    • trophogenic zone = PS > R

      • photic zone = >1% incident light

    • tropholytic zone = R > PS

      • aphotic zone = below 1% incident light

    • PS = photosynthesis

    • R = respiration

  • zones defined by temperature

    • epilimnion: The upper layer of water in a stratified lake, characterized by warm temperatures and abundant sunlight, which supports high levels of photosynthesis.

    • metalimnion: The middle layer of water in a stratified lake, where temperatures begin to decrease and light penetration diminishes, leading to a decrease in photosynthesis activity.

    • hypolimnion: The lowest layer of water in a stratified lake, which is typically cold and dark, with minimal photosynthesis occurring due to lack of sunlight and where decomposition processes are more pronounced.

  • Hydrologic Cycle: how water gets to low points of the depth of lake

    • 1) Precipitation: rain or snow

    • 2) Evaporation

    • 3) Surface and groundwater: directly in/out of lake

  • Water balance

    • Water income = precipitation (coming directly into lake), surface runoff (coming from streams and rivers), and groundwater

    • Water losses = outlet, evaporation (brings water back up into percipitation), and seepage (sinking out)

  • Evapotranspiration: water loss through transpiration of vegetation

    • ex. trees taking in vastes amounts of water and then pumping in/out into evaporation

    • causes flooding because the tree is not taking in water from the ground

  • Open basins = inflows and outflows

  • Closes basins = no inflows and outflows

    • lake bowls that are purely dependent on precipitation and evaporation

    • as water evaporates it leaves salt behind so the lake becomes salty

  • Water residence time (flushing time): how long does it take for the water to completely replace itself

    • the longer it takes to flush the more pollution will occur

  • Residence time = Volume/Flow

  • Flow = precipitation + surface water inflow + groundwater inflow