Large River Floodplain Ecology

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Large River Floodplain Ecology
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Construction of levees along the Mississippi
River and many of its tributaries has severed the
river from over 90 of its floodplain, denying
fish and other aquatic species access to millions
of acres of foraging, spawning and nursery
habitat. Miss. Dept. of Archives and
History Miss. Dept. of Archives and History
http//www.lmrcc.org/ARMP20folio.pdf
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Wicander and Monroe 1993
Sale Cypremont 4,600 7,000 years
ago Cocodrie 3,500 4,600 years
ago Teche 2,800 3,500 years
ago
St. Bernard 1,000 2,800 years ago Lafourche
300 1,000 years ago Plaquemine 500 750
years ago
Balize present 500 years ago
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Oxygen Level Controls
Photosynthesis produces oxygen Solar Energy
CO2 H20 ? C6H12O6 O2 Respiration consumes
oxygen C6H12O6 O2 ? CO2 H20 chemical
energy(ATP)
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Net Primary Production (measure of produced
energy)
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What is Hypoxia

• Dissolved Oxygen less than 2.0 mg/L
• Normoxic DO gt 2.0 mg/L
• Generally, most fish can not tolerate hypoxic
  conditions for long periods.
• Gar, bowfin (choupique), bullheads can

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Why Hypoxia?

• During low water times, the dry lands are
  extremely fertile and grow a lot of plants.
• When the spring floods come and temperatures
  rise, bacteria begin to decompose the vegetation
  on the floodplain floor.
• Bacterial respiration is what removes the oxygen
  (lack of flushing in backwater habitats
  contributes).
• Respiration rates exceed photosynthetic rates.

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High Water vs. Low Water
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When and Where Is Hypoxia?

• Generally found during high water times when
  temperatures are warm.
• Backwater areas (away from the mainstem river).
• Low flow

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Eventually the swamp drains and backwater areas
become very productive.
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Three General Types of Water

• Brown
• High flow, lots of sediment, fairly high oxygen
  levels, riverine
• Green
• Low flow, stratification, very high surface
  oxygen levels, highly productive, lacustrine
• Black
• Low flow, very low surface oxygen levels, not
  productive, swamp

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December
June
August
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How Do Unproductive Areas Support Living
Populations?

• Submerged Aquatic Vegetation
• Oxygen Refuge
• Productive microhabitats

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Fish and Aquatic Vegetation

• Densities of young fish are often greater in
  aquatic vegetation than in adjacent open water

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Mean Surface Dissolved Oxygen in Open Water and
Plants at Each Site
Green
Brown
Black
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Air-Water Interface
Atmospheric oxygen diffuses into water
Fish pipe at the microsurface layer


Low DO Water
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How Do Unproductive Areas Support Living
Populations?

• Detritus-Based Production
• Decomposers (e.g., bacteria) transfer energy
  stored in old organic matter to consumers
• Insects, crawfish
• Low-oxygen tolerant organisms
• Gar, bowfin (choupique), bullheads

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Energy flow through an aquatic ecosystem.
From Cole 1988, Waveland Press
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Detritus Based Food Web
From Cole 1988, Waveland Press