Brenda C' Nieto

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Flow Pulse Effects on the Macroinvertebrate
Community Structure in the Rio Salado, an Arid
Stream Ecosystem

• Brenda C. Nieto

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Outline

• Aim
• Introduction
• Arid land stream ecosystems
• Flow pulses versus floods
• Macroinvertebrate communities
• Hypothesis and specific goals
• Material and methods
• Preliminary results and conclusions

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Aim

• Professional
• Understand the interdisciplinary field of
  Environmental Sciences and Ecology
• Personal
• Have skills and knowledge for future scientific
  research and collaborate with other research and
  colleagues for experience.
• Scientific
• Study the effects of flow pulses on the
  macroinvertebrate community

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Arid Land Stream Ecosystems

• Exist in setting defined by water limitation
• Periods of declining or absent flow
• Extremes in magnitude and variance of discharge
• Warm temperatures and sunlight create high rates
  of production

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Flow Pulses vs. floods
Flow Pulse- high flow that does not exceed the
threshold of sediment motion. Flood- high flow
that involves sediment motion and therefore
becomes a disturbance.
Disturbance threshold
Flow Pulse
Flood
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Flow Pulses vs. floods
Initiation of sediment motion
Surface
Abrasion by bedload
Flow
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Macroinvertebrate communities
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Macroinvertebrate CommunitiesCommon Invertebrates
Culicidae
Mosquitoes
Water Mites
www.ru.ac.za
Midge
Mayflies
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Macroinvertebrate CommunitiesCommon Invertebrates
Water Boatman
Riffle Beetles

• Black Flies
• Filter feeding
• many nutrients (nitrogen and/or phosphorus) in
  water

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Macroinvertebrates and Hydrology

• Rio Salado is a temporal and spatial
  intermittent stream.
• Desert streams are characterized by flash floods
  and droughts.
• Effects of floods and droughts as a disturbance
  are well studied but less is known about flow
  pulses.

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Hypothesis and Specific goals

• The effects of flow pulses after a long drought
  period will increase the density of
  macroinvertebrates and change the composition of
  substrates.
• To see the differential effect of flow pulses in
  different habitats.

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Study Site
Rio Salado
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Study Site
Substrates
Sand 88
Cobble/Gravel 11
Back-waters 1
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Methods and Materials

• Equipment
• 2420cm sample surface border
• Net
• Large Pan
• No. 35 graded sieve
• 26 plastic cups
• Ethanol

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Methods and Materials

• In June and repeated in July
• 5 samples were taken from Sand
• 5 samples from Gravel
• 3 samples from Back-waters

Placed into cups with 70 Ethanol Sorted with
Leica Stereozoom 4 microscope Isolated
macroinvertebrates in cups Identified to family
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Preliminary Results and Conclusions
During Drought (June) 194.9 macroinvertebrates
per m²
After Flow Pulse (July) 418.9 macroinvertebrates
per m²
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Preliminary Results and Conclusions
Density Increased in Cobble Density Decreased
in Back-waters Density Increased in Sand
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Preliminary Results and Conclusions

• Macroinvertebrates By Substrate
• Hyrdracarina appeared in sand and cobble
• Chironomidae largest increase in back-waters
• Culicidae decreased in sand
• Corixidae decreased in back-water
• Simuliidae increase in cobble

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Preliminary Results and Conclusions

• July Results Compared to June
• Hydracarina present
• Increase in Chirononmidae in all 3 substrates
• Culicidae increased in cobbles
• Baetidae remained similar
• Corixidae increased in cobble decreased
  back-waters
• Simuliidae increased in cobble and back-water
• Elmidae decreased

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Preliminary Results and Conclusions

• General Patterns
• Macroinvertebrates density increased after flow
  pulse.
• Massive emergence Chironomidae, may relate with
  an increase of habitat extent and increase in
  sediment moisture
• Eggs in sediment
• Flow pulse involved a change in the community
  composition

• Difference in Substrate
• Some families found in one habitat, are
  specialized
• Reduction in habitat conditions of back-waters
  caused Corixidae decrease
• Sand and cobbles were more stable in terms of
  composition

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Acknowledgements
U.S. Fish and Wildlife Vicenç Acuña
Salazar Jennifer Johnson Mike Friggens John
Craig Alex Benhumea Tara Blackman Tierney
Adamson Caitlin Smith Ashwana Fricker Fred