Transcript Benthic Macroinvertebrate Response to Hydrogeomorphic

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
Complexity in the Kaw
Low Water – High Complexity
High Water – Low Complexity
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?
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
Great Plains Rivers
• Very little wood
• Estimate only 0.06% of
total habitat
– 0.0006 m2 wood/m2
sand
• Kansas River – If found,
in extremely local areas
• Flushed downstream by
large flashy spates.
•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
Measuring River Complexity
R2=0.91
Discharge
Complexity
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.
Methods
7/7 RCR=1.36
8/3 RCR=1.47
8/31 RCR=1.55
7/20 RCR=1.54
8/18 RCR=1.2
9/29 RCR=1.46
Discharge (m3 * s-1)
RCR
6/4 RCR=1.02
Methods
• Collected over 500 zoobenthic cores
– 7 dates throughout summer
– Elutriated and collected in 100 μm sieve
Results - Benthic Community
dominated by:
Other Diptera
1%
Oligochaetes
3%
Ceratopogonidae
9%
– Diptera
• Chironomidae
• Ceratopogonidae
– Oligochaetes
– Other Insects
Chironomidae
85%
Other Invertebrates
2%
• Insects identified to genus
• Chironomids
– Tanytarsus
– Polypedilum
– Rheotanytarsus
– Krenosmittia
– Partendipes
– Lopescladius
– Rheosmittia
– Saetheria
• Ceratopogonids
– Culicoides
• Polypedilum and Tanytarsus found
throughout all areas of the river
•Lopescladius and Rheosmittia generally
found in main channel
Large pulses
completely wipe
out community
Smaller spikes in
flow eliminate
community in high
stress areas
Discharge
Complexity
• Hypothesis 1 – Different river complexity
levels have distinct communities.
Medium Complexity
Low Complexity
High Complexity
•NMS – 3d solution
-Low stress (8.8)
-Low Instability
0.00048, 31 iterations
•MRPP – Three
communities significantly
different
-Chance within group
agreement
A = 0.021, p < 0.001
• Hypothesis 2 –Slackwaters communities
are different from main-channel river.
Side-channel Slackwater
•Natural Experiment
Secondary channel –
periodically cut off into a
slackwater
•NMS allows us to follow
community through time
•Community switches back
and forth
•Date 7 – Slowly flowing
tertiary channel
•More similar to
slackwater community
• 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
Strategies for living in the Kaw
Resisting Disturbance
•Few inverts found
consistently in the
main channel
– Some small genera
• Krenosmittia,
Lopescladius, Rheosmittia
– Some larger
• Paratendipes,
Polypedilum, Robackia,
Saetheria
– Probably burrowing
Fleeing the System
•Desert
invertebrates
commonly flee
flash floods
•Desert inverts
larger, hard
bodied
•River is too
wide
Finding Refuges
• Hard substrates unavailable
• Unprotected areas lost more
species during flow spates
• Habitat heterogeneity increase
species diversity
•Not all refuges protect from
the largest floods
•Sandbars create areas for
recolonization
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
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
• 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