Large River Floodplain Ecology

1. Large River FloodplainEcology

3. 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

4. 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

11. Oxygen Level Controls Photosynthesis produces oxygen: Solar Energy + CO2 + H20  C6H12O6 + O2 Respiration consumes oxygen: C6H12O6 + O2 CO2 + H20 + chemical energy(ATP)

12. 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)

13. 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

14. WhyHypoxia? • 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.

16. High Water vs.Low Water

18. When and Where Is Hypoxia? • Generally found during high water times when temperatures are warm. • Backwater areas (away from the mainstem river). • Low flow

19. Eventually the swamp drains and backwater areas become very productive.

20. 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

21. Backwater Interior Lakes Mainstem December June August

22. 8 9 7 6

23. How Do ‘Unproductive’ Areas Support Living Populations? • Submerged Aquatic Vegetation • Oxygen Refuge • Productive microhabitats

24. Fish and Aquatic Vegetation • Densities of young fish are often greater in aquatic vegetation than in adjacent open water

25. Normoxic Hypoxic Mean Surface Dissolved Oxygen in Open Water and Plants at Each Site Green Brown Black

26. Air-Water Interface Atmospheric oxygen diffuses into water Fish ‘pipe’ at the microsurface layer Low DO Water

27. 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

28. Energy flow through an aquatic ecosystem. From Cole 1988, Waveland Press

29. Detritus Based Food Web From Cole 1988, Waveland Press