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Brian O’Neill

Ecological Responses to Hydrogeomorphic Fluctuations in a Sand Bed Prairie River: River Complexity, Habitat Availability, and Benthic Invertebrates. Brian O’Neill. Kansas River. The Kaw upstream of Lawrence. Looking upstream along Lawrence levee. Variability in the Kaw.

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Brian O’Neill

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  1. Ecological Responses to Hydrogeomorphic Fluctuations in a Sand Bed Prairie River: River Complexity, Habitat Availability, and Benthic Invertebrates Brian O’Neill

  2. Kansas River The Kaw upstream of Lawrence Looking upstream along Lawrencelevee

  3. Variability in the Kaw

  4. Complexity in the Kaw Low Water – High Complexity High Water – Low Complexity

  5. Questions • Effect of hydrogeomorphic fluctuations? • Role of complexity and variability? • Coping with continuous habitat rearrangement? • Lack of stable substrate, what habitats are used? • Role of slackwater habitats? • Useful life strategies and adaptations?

  6. Sand Bed Rivers • Prevailing wisdom - woody debris is main habitat for benthos • Up to 1/3 of total habitat is wood • (~0.5m2 wood/m2 sand) • Most studies done in forested rivers of the Southeast Sipsey River, AL

  7. Great Plains Rivers • Kansas River – If found, in extremely local areas • Flushed downstream by large flashy spates. • Very little wood • Estimate only 0.06% of total habitat • 0.0006 m2 wood/m2 sand • Historically Kansas River never had much wood (Tidball, 1853) • Never had de-snagging operations • Where are benthos living? • Slackwaters – Habitat in great abundance in prairie rivers

  8. R2=0.91 Measuring River Complexity Discharge Complexity

  9. Hypotheses • H1 – Different river complexity levels have distinct benthic communities. • H2 –Slackwaters different than main-channel communities. • H3 – Sheltered areas rebound faster and have higher densities of zoobenthos.

  10. Methods

  11. Methods • Collected over 500 zoobenthic cores • 7 dates throughout summer • Elutriated and collected in 100 μm sieve

  12. Results - Benthic Community dominated by: • Diptera • Chironomidae • Ceratopogonidae • Oligochaetes • Other Insects

  13. Insects identified to genus • Chironomids • Tanytarsus • Polypedilum • Rheotanytarsus • Krenosmittia • Partendipes • Lopescladius • Rheosmittia • Saetheria • Ceratopogonids • Culicoides

  14. Polypedilum and Tanytarsus found throughout all areas of the river • Lopescladius and Rheosmittia generally found in main channel

  15. Smaller spikes in flow eliminate community in high stress areas Large pulses completely wipe out community Discharge Complexity

  16. Hypothesis 1 – Different river complexity levels have distinct communities. • NMS – 3d solution • -Low stress (8.8) • -Low Instability • 0.00048, 31 iterations Medium Complexity • MRPP – Three communities significantly different • -Chance within group agreement • A = 0.021, p < 0.001 Low Complexity High Complexity

  17. Natural Experiment • Secondary channel – periodically cut off into a slackwater • NMS allows us to follow community through time • Hypothesis 2 –Slackwaters communities are different from main-channel river. Side-channel Slackwater • Community switches back and forth • Date 7 – Slowly flowing tertiary channel • More similar to slackwater community

  18. Hypothesis 3 – Sheltered areas rebound faster and have higher densities of zoobenthos. • Sheltered areas • - Richness loosely • correlated with • complexity • - r2=0.22, p=0.14 • Main-channel areas • - Richness • correlated • - r2=0.5, p<0.001

  19. Strategies for living in the Kaw

  20. Resisting Disturbance • Few inverts found consistently in the main channel • Some small genera • Krenosmittia, Lopescladius, Rheosmittia • Some larger • Paratendipes, Polypedilum, Robackia, Saetheria • Probably burrowing

  21. Fleeing the System • Desert inverts larger, hard bodied • River is too wide • Desert invertebrates commonly flee flash floods

  22. Finding Refuges • Not all refuges protect from the largest floods • Sandbars create areas for recolonization • Hard substrates unavailable • Unprotected areas lost more species during flow spates • Habitat heterogeneity increase species diversity

  23. Prairie River Inverts • Adapted to exploit the exposed river structures • Small • Short lived • Multivoltine • Many species use river structures as nurseries • Slackwater areas important to benthic community • Sustainable food web needs slackwater areas

  24. Implications of Natural Complexity • Levees greatly reduce complexity of the river • Complexity reduction • Reduces fish stock • Sediment retention is reduced • Deteriorating water quality • Economic losses • Jungwirth 93, Naiman 88 • Dissertation jumps directly into the question of how the food web copes with hydrogeomorphic fluctuations

  25. Funding provided by: • Kansas Biological Survey • Kansas Applied Remote Sensing • Kansas Academy of Science • National Science Foundation • KU EEB • Thanks to • Sarah Schmidt • Brad Williams • Andrea Romero • Munique Webb • PieroProtti

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