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Hydrogeomorphic Fluctuations in a Sand Bed Prairie River: Impacts on Benthic Invertebrate Communities

This study investigates the relationship between hydrogeomorphic fluctuations and benthic invertebrate communities in the Kansas River, a sand bed prairie river. It explores the effects of river complexity and variability, focusing on how habitat use varies between slackwater and main-channel areas. The findings reveal that the community composition is influenced by the hydrology of the river, with significant differences in benthic communities across complexity levels. The research highlights the critical role of slackwater habitats in sustaining aquatic ecosystems amidst natural variability.

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Hydrogeomorphic Fluctuations in a Sand Bed Prairie River: Impacts on Benthic Invertebrate Communities

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  1. Hydrogeomorphic fluctuations in a sand bed prairie river: benthic invertebrates, river complexity, and habitat use Brian O’Neill James H.Thorp

  2. Kansas River River Complexity River Variability Low Water – High Complexity High Water – Low Complexity

  3. Implications of Natural Variability • Dammed tributaries greatly reduced variability • Global climate change expected to increase precipitation variability • Depending on dam managing strategy, increased variability may make hydrology more similar to historic levels

  4. 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

  5. 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

  6. 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?

  7. R2=0.91 Measuring River Complexity Discharge Complexity

  8. 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.

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

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

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

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

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

  14. 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

  15. 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

  16. 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

  17. Implications of Natural Complexity • Slackwater areas important to benthic community • Levees greatly reduce complexity of the river • Sustainable food web needs slackwater areas • Dissertation jumps directly into the question of how the food web copes with hydrogeomorphic fluctuations

  18. 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 • Piero Protti

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