Presentation by Julian D. Olden at the Annual Meeting of the North American Benthnological Society (2009)

1. Turning dreams into reality
Challenges to developing flow-ecological
relationships to support streamflow management
Julian D. Olden
Cathy A. Reidy Liermann
School of Aquatic & Fishery Sciences
University of Washington, Seattle, WA

2. Water and the vitality of rivers
• Flow variability shapes the physical,
chemical and biological attributes and
functioning of riverine systems
– Channel form and habitat complexity
Freshwaters Illustrated
– Life-history patterns
– Lateral and longitudinal connectivity
– Resistance to species invasions
• At the same time, human societies
modify natural flow regimes to provide
dependable ecological services and to
Freshwaters Illustrated
seek protection from floods and
droughts

3. Water links society and nature
• Global concerns about the sustainability of human water use
practices have grown markedly in recent years
• People clearly benefit from the
direct use of water, but there
are limits to the amount of
water that can be withdrawn
from river systems
• There is a need to understand
the relationships between river
flow regimes and the in-stream
aquatic and riparian ecosystems
that they support
Wallace et al. (2003)

4. Challenge Synopsis
• Many of the hierarchical linkages
between the ecological response
to hydrology are poorly
understood, inadequately
validated, and remain expressed
largely as descriptive hypotheses
rather than predictive or
quantitative models.
What must we know, what can we reasonably learn, and
what do we simply need to treat as uncertainty in the
development of flow:ecology relationships for river
management?

5. Major hurdles to linking ecological
responses to riverine hydrology
Devising testable hypotheses
from general principles
Generating models
Informing decision
that are realistic,
support tools
mechanistic and
defendable
Accounting for uncertainty
(data, parameter, model,
knowledge)

6. Characterizing flow regimes
Hydrologic metrics characterize statistical properties of the long-
term hydrologic regime of rivers based on multi-year time series
of discharge data.
Important considerations for metric selection:
– Sensitivity to natural and human drivers of hydrologic change
– Uncertainty in their estimation (bias and precision)
– Amenability to direct or indirect management actions
– Independence from other hydrologic indices (X)
The difficulty in developing predictive flow:ecology relationships
may be due in part to the inappropriate selection or uncertain
estimates of hydrologic metrics used as model predictors.

7. Uncertainty in metric estimation
Uncertainly in metric estimation is a function of:
• Length of flow record
• Period of flow record
• Number of years of overlap Sauk R.
Kettle R.
Quinault R. Stehekin R.
1.0 Skokomish R.
Standardised MSE averaged
across all hydrologic metrics
0.8 American R.
Naselle R.
East Fork Lewis R.
0.6 Cispus R.
0.4
0.2
0.0
0 5 10 15 20 25 30 35 40
Number of years

8. Uncertainty in metric estimation
15 year period of record
0.6
Standardized MSE
0.5
0.4
0.3
0.2
0.1
0.0
Magnitude Frequency Duration Timing RC
General recommendations (Kennard et al., in press, River Res. Appl.)
• Metric estimation must be based on at least 15 years of discharge data
• Metric estimation should be based on overlapping discharge records
contained within a discrete temporal window (ideally >50%)
• Metric uncertainty varies greatly and should be accounted for when
developing flow:ecology relationships.

9. Characterizing ecological response
Ideally, ecological response variables should be:
– Sensitive to existing or proposed flow alterations
– Differentially sensitive to other sources of human impact
– Amenable to monitoring
– Valued by society
Some composite ecological indices may be useful if they correlate
with human-induced changes in streamflow (e.g., Lotic-
invertebrate Index for Flow Evaluation: Extence et al. 1999)
Recent studies have demonstrated that ecological responses to flow
variation and alteration can be inferred based on the biological
attributes of species (e.g., resource and habitat utilization, life
history)

10. Characterizing ecological response
• Taxon-free metrics allows for the comparison of species
compositions that naturally differ due to biogeographic
constraints on regional species pools
• The sensitivity and time scale of ecological change will depend
on the organism, or group of organisms, in question
Habitat specialists Habitat generalists
Freeman and Marcinek (2006)

11. Scales of ecological responses
• There has been few attempts to reconcile the mismatch in scales
between the hydrological change and the ecological response.
Seasonal timing
Inter-annual variability & predictability Flood magnitude
50 50 Flood 50
10 frequency Rate of
10 rise & fall
10
1 1
Discharge
0.1 0.1
1
0.01 0.01 Low
flow Flood
duration duration
0.001 0.001 0.1
1990 April
m
n
1975 1980 1985 1990 1995 2000
r
t
Au
Sp
Wi
Su

12. Scales of ecological responses
• Species occurrence at a particular location and time may be
shaped by long-term flow dynamics, whereas the relative
abundance or biomass of species is more likely driven by
short-term flow events.
Mary River, Australia
Presence-Absence (87%) Abundance (62%) Biomass (58%)
14
14 14
12
12 12
Relative contribution (%)
10 10 10
8 8 8
6 6 6
4 4 4
2 2
2
0 0
Long-term flow regime Short-term flow events Long-term flow regime Short-term flow events 0
Long-term flow regime Short-term flow events
Data from Kennard et al. (2007)

13. Spatial and temporal mismatch
30
• Limited spatial and temporal 25
# gauge-sample pairs
coverage of both stream gauges and 20
biological samples 15
10
5
• e.g., WA REMAP: summer surveys
0
(July-Sept) in 1993-1994 (Coastal) 0 5 10 15 20
and 1999-2000 (Cascades)
20
# of gauge-sample pairs
15
• Observations made on a single scale 10
can, at best, capture only those
riverine patterns and processes 5
pertinent to that scale of observation 0
0 5 10 15 20 25 30
Watercourse distance (km)

14. Multiple limiting factors
• The development of robust flow–ecology relationships will need
to take into account the role that other environmental factors
play in shaping ecological patterns in streams and rivers
• Our ability to disentangle the effects
of multiple limiting factors will
benefit from recent statistical
advancements and targeted
monitoring activities
• We must carefully reconcile the
advantages of more complex
modeling approaches with the need
to develop assessable science that
informs decision support tools
Swift (1979)

15. Summary
• Until we better understand the relationships between ecological
health and the magnitude of hydrological alteration, we will not be
able to mount a convincing argument in support of environmental
flow management.
General recommendations
• Agreement on a core suite of headline ecological and hydrologic
indices
• Modeling that recognize the scales of ecological responses to
hydrologic alteration
• Greater data sharing among the academic community
• Initiation of new monitoring programs that target

16. Acknowledgments
• Tim Beechie, Chris Konrad, NOAA Fisheries