Transcript Document

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
Maringouin:
Teche:
St. Bernard Delta:
Lafourche Delta:
6,000 – 7,000 years ago
5,700 – 3,900 years ago
4,600 – 1,800 years ago
3,400 - 400
Oxygen Level Controls
Photosynthesis produces oxygen:
Solar Energy + CO2 + H20  C6H12O6 + O2
Respiration consumes oxygen:
C6H12O6 + O2  CO2 + H20 + chemical energy(ATP)
Net Primary Production (measure
of produced energy)
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
Average net primary productivity (kcal/m2/yr)
8,000
8,800
9,600
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.
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
December
June
August
Interior Lakes
Mainstem
8
9
7
6
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
Mean Surface Dissolved Oxygen in Open
Water and Plants at Each Site
Dissolved Oxygen (mg/L)
16
Green
14
12
Brown
10
Black
Open
8
Plant
6
4
2
0
GLN
GLS
INT
Normoxic
FL
BL
SOC
Hypoxic
Air-Water Interface
Atmospheric oxygen
diffuses into water
Fish ‘pipe’ at the
microsurface layer
Low DO Water
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