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Large River Floodplain Ecology. 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. - PowerPoint PPT Presentation
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Large River Floodplain Ecology
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/ARMP%20folio.pdf
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
Oxygen Level Controls
Photosynthesis produces oxygen:Solar Energy + CO2 + H20 C6H12O6 + O2
Respiration consumes oxygen:C6H12O6 + O2 CO2 + H20 + chemical energy(ATP)
Estuaries
Swamps and marshes
Tropical rain forest
Temperate forest
Northern coniferous forest (taiga)
Savanna
Agricultural land
Woodland and shrubland
Temperate grassland
Lakes and streams
Continental shelf
Open ocean
Tundra (arctic and alpine)
Desert scrub
Extreme desert
800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600
Average net primary productivity (kcal/m2/yr)
Net Primary Production (measure of produced energy)
What is Hypoxia• Dissolved Oxygen less than 2.0 mg/L
• Normoxic = DO > 2.0 mg/L
• Generally, most fish can not tolerate hypoxic conditions for long periods.– Gar, bowfin (choupique), bullheads can
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.
High Water vs. Low Water
When and Where Is Hypoxia?
• Generally found during high water times when temperatures are warm.
• Backwater areas (away from the mainstem river).– Low flow
Eventually the swamp drains and backwater areas become very productive.
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
Backwater Interior Lakes Mainstem
December
June
August
6
7
8 9
How Do ‘Unproductive’ Areas Support Living Populations?
• Submerged Aquatic Vegetation
– Oxygen Refuge
– Productive microhabitats
Fish and Aquatic Vegetation
• Densities of young fish are often greater in aquatic vegetation than in adjacent open water
0
2
4
6
8
10
12
14
16
GLN GLS INT FL BL SOC
Diss
olve
d O
xyge
n (m
g/L)
Open
Plant
Normoxic Hypoxic
Mean Surface Dissolved Oxygen in Open Water and Plants at Each Site
Green
Brown Black
Air-Water Interface
Low DO Water
Atmospheric oxygen diffuses into water
Fish ‘pipe’ at the microsurface layer
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
Energy flow through an aquatic ecosystem.
From Cole 1988, Waveland Press
Detritus Based Food Web
From Cole 1988, Waveland Press