Flows and Transport in Rivers - Hydro-Environmental Analysis: Freshwater Environments - page 115

TABLE 4.8
IHA Parameters and Their Ecosystem Inluences

IHA Parameter
Group Hydrologic Parameters Ecosystem Inluences

1. Magnitude of
monthly water
conditions

Mean or median value for each
calendar month

• Habitat availability for aquatic organisms
• Soil moisture availability for plants
• Availability of water for terrestrial animals
• Availability of food/cover for fur-bearing mammals
• Reliability of water supplies for terrestrial animals
• Access by predators to nesting sites
• Inluences water temperature, oxygen levels, and photosynthesis
in water column

Subtotal 12 parameters

2. Magnitude
and duration
of annual
extreme water
conditions

Annual minima. 1-day mean
Annual minima. 3-day means
Annual minima. 7-day means
Annual minima. 30-day means
Annual minima, 90-day means
Annual maxima. 1-day mean
Annual maxima. 3-day means
Annual maxima. 7-day means
Annual maxima. 30-day means
Annual maxima. 90-day means
Number of zero-low days
Base low index: 7-day minimum
low/mean low for year

• Balance of competitive, ruderal, and stress-tolerant organisms
• Creation of sites for plant colonization
• Structuring of aquatic ecosystems by abiotic vs. biotic factors
• Structuring of river channel morphology and physical habitat
conditions
• Soil moisture stress ill plants
• Dehydration in animals
• Anaerobic stress in plants
• Volume of nutrient exchanges between rivers and loodplains
• Duration of stressful conditions such as low oxygen and
concentrated chemicals in aquatic environments
• Distribution of plant communities in lakes, ponds, and loodplains
• Duration of high lows for waste disposal, aeration of spawning
beds in channel sediments Subtotal 12 parameters

3. Timing of
annual
extreme water
conditions

Julian date of each annual 1-day
maximum
Julian date of each annual 1-day
minimum

• Compatibility with life cycles of organisms
• Predictability/avoidability of stress for organisms
• Access to special habitats during reproduction or to avoid
predation
• Spawning cues for migratory ish
• Evolution of life history strategies, behavioral mechanisms

Subtotal 2 parameters

4. Frequency
and duration
of high and
low pulses

Number of low pulses within
each water year
Mean or median duration of low
pulses (days)
Number of high pulses within
each water year
Mean or median duration of
high pulses (days)

• Frequency and magnitude of soil moisture stress for plants
• Frequency and duration of anaerobic stress for plants
• Availability of loodplain habitats for aquatic organisms
• Nutrient and organic matter exchanges between river and
loodplain
• Soil mineral availability
• Access for waterbirds to feeding, resting, and reproduction sites
• Inluences bedload transport, channel sediment textures, and
duration of substrate disturbance (high pulses) Subtotal 4 parameters

5. Rate and
frequency of
water
condition
changes

Rise rates: Mean or median of
all positive differences between
consecutive daily values
Fall rates: Mean or median of all
negative differences between
consecutive daily values
Number of hydrologic reversals

• Drought stress on plants (falling levels)
• Entrapment of organisms on islands, loodplains (rising levels)
• Desiccation stress on low-mobility stream edge (varial zone)
organisms

Subtotal 3 parameters
Grand total 33 parameters

Source: Nature Conservancy, Indicators of hydrologic alteration, Version 7 user's manual, The Nature Conservancy,
Arlington, VA, 2007. With permission.