The Structure of Aquatic Ecosystems

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The Structure of Aquatic Ecosystems

• Created by Dave Werner
• MATES

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5 Major Elements of Lake Structure

• 1. Morphometry
• 2. Physical
• 3. Chemical
• 4. Biological
• 5. Watershed Airshed

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Lakes

• 1. Morphometry function of underwater contour
  lines, the shape of the lake, its geologic
  origin.
• Lakes Morphometry is basic to its structure
• For example, when we know the shape and structure
  of a lake basin, we can sometimes predict how
  weather conditions or human-induced events may
  affect water levels in that system.
• Still lakes lentic environments
• Flowing lotic systems, streams

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Hypsographic Curves

• are graphs used to provide a visual
  representation of the relationship between the
  surface area of a lake basin and its depth. With
  these graphs, we can be more accurate in
  predicting how a lakes surface area could change
  based on changes in water depth. Figure 3-2

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Figure 3-1 A bathymetric map created by Florida
LAKEWATCH.

• This approach gives us a visual estimation only.
  If we were to calculate the surface area within
  each one of the contour lines in Figure 3-1and
  then plot them on a graph, wed have a
  hypsographic curve a visual image that can give
  us accurate information at a glance.

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Hypsographic Curve
Figure 3-2 A hypsographic curve drawn for Lake
Denton. Notice that the x-axis is located at the
top of the figure. This is a common format for
this type of graph as it allows depth
measurements to be displayed in a downward
direction.
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Why are hypsographic curvesimportant?

• Used for predicting the best time to implement
  various lake management strategies such as
  aquatic plant management, habitat restoration,
  muck removal activities, etc.
• From a lake residents standpoint, being able to
  visualize and/or predict a lakes surface area
  during high, medium, or low water levels can
  certainly be helpful in planning the location for
  a new lakefront home or dock.
• Useful for comparing lakes and explaining why
  some lakes are more susceptible to changes in
  lake surface area while others of similar size
  (i.e., surface area) may show very little change.

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Scientists use hypsographic curvesfor predicting
two lake dynamics inparticular

• (1) a lakes ability to dilute incoming materials
• (2) the potential for lake water mixing.

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2. Light Temperature

• 2 major zones
• Littoral
• Pelagic or limnetic

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Light Temperature

• Light Zonation
• Photic/Euphotic Zone
• Aphotic Zone/Profundal
• Sublittoral Zone The deepest area of plant
  growth.

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Temperature Zonation

• As light energy is absorbed by water, it is
  converted to heat energy, which results in the
  warming of the lake-surface water.
• During summer, thermally stratified lakes are
  warmer at the top and cooler at the bottom.
• The warm surface layer is called the epilimnion,
  and the cooler bottom layer the hypolimnion.
• The zone of rapid temperature decline in the
  water column from shallow to deep water is called
  the thermocline or the metalimnion.

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3. Chemical Factors

• The depth at which rapid change in a substance
  occurs.
• The Berkeley Pit is a chemically layered system,
  which means that the chemistry of the water
  changes with depth. The brownish-red water at the
  surface is actually the least contaminated water
  in the pit, and the deeper it gets, the worse the
  water quality. The color changes as well, going
  from brownish-red on top to bluish green at the
  bottom.
• At a certain depth, the chemistry of the water
  changes so rapidly that it forms a chemical
  boundary scientists refer to as the chemocline
  (see illustration and graphs). Water above the
  chemocline is chemically lighter (i.e., less
  dense) than the water below. The layering of the
  two waters is like oil floating on water. The
  water above the line is also less acidic (higher
  pH), with lower concentrations of metals. The two
  layers of water (above and below the chemocline)
  act like fresh water floating on salt water,
  never mixing unless stirred.

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4. Biological Zonation

• Plankton
• Nekton
• Neuston - surface
• Pleuston Large floating assemblages
• Attached Algae Littoral Zone
• Aquatic Macrophytes Higher plants, likely to
  dominate sandy or muddy littoral zones
• Aufwuchs - the small animals and plants that
  encrust hard substrates, such as rocks, in
  aquatic environments. Ex Algae, fungi, bacteria,
  protozoa.
• Benthic/Benthos
• Epifaunal
• Infaunal

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5. Watershed Airshed

• The size, slope, geologic composition, climate
  of the lakes drainage basin influence the
  identity quantity of minerals suspended or
  dissolved in the lake or deposited in the
  sediment.

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Ponds vs. Lakes

• Pond generally smaller than a lake.
• Lake A large inland body of water, fresh or
  salt.
• The Manahawkin Lake can be found on the West
  Creek USGS quad topo map. Manahawkin Lake is a
  reservoir in Ocean County in the state of New
  Jersey. The latitude and longitude coordinates
  for this reservoir are 39.6965, -74.2601 and the
  altitude is 23 feet (7 meters).

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Streams Rivers

• River larger fast moving, often warmer.
• Stream smaller, usually lead to larger rivers.
• These are Lotic systems defined by water flow.
• Discharge (volume per time)
• Current (distance per time)

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Meandering
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Example

• http//www.classzone.com/books/earth_science/terc/
  content/visualizations/es1306/es1306page01.cfm?cha
  pter_novisualization

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Biological Structure of Streams

• Drift Living benthic invertebrates algae that
  have released or lost their attachment to
  substrate. Optimum food supply for fish
  inverts.
• Detritus dead organic fragments coated w/
  bacteria, fungi, small protozoans.

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Estuaries

• Where the river meets the sea.
• Structure is modified by
• Morphometry
• Tide
• Inflowing FW
• Salt Wedge

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Salt Wedge

• Salt Wedge Animation

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Wetlands

• Marshes, swamps, or bogs
• Vegetation most important structural elements
  (emergent macrophytes, trees, Sphagnum moss).