Environmental Engineering Reference
In-Depth Information
In order to assess the natural condition, Richter et al. (1996, 1997) developed the indicators
of hydrologic alteration (IHA) method and the corresponding program distributed by The Nature
Conservancy (2007) and discussed in Chapter 4. The IHA method characterizes the range of varia-
tion of discharge at a site by using a suite of 33 hydrologic indices. The RVA typically involves
(available at: http://www.epa.gov/watertrain):
Characterizing the range of lows using a series of hydrologic parameters (such as the IHA
method described in Chapter 4; The Nature Conservancy 2007).
Selecting low management targets based on these parameters.
Designing a management system that will attain these targets.
Implementing the management system and monitoring its effects.
Repeating characterization yearly and comparing new values to the management targets.
Incorporating new monitoring information and revising either the management system or
the RVA targets as necessary.
7.4.3 H ydroecoLoGIcaL I nteGrIty p roceSS
The hydroecological integrity assessment process (HIP) (Henriksen et al. 2006) developed by the
U.S. Geological Survey (USGS) was also designed (as was the IHA method discussed in Section
7.4.2 and in Chapter 4) to determine hydrologic alteration, or to manage streamlow and establish
low standards. The HIP method involves an evaluation and classiication of relatively unmodiied
streams in a geographic area, based on 171 ecologically relevant indices computed from the avail-
able data for daily mean discharges and peak annual lows.
Once the indices are computed, they are evaluated based on a review by Olden and Poff (2003)
of the available hydrologic indices as tested using data from 420 sites around the United States.
Following the analysis of the indices, a series of principal components analyses are used to identify
the most signiicant indices associated with 10 subcomponents of the low regime for each of the
6 stream types:
Magnitude—low, average, high
Frequency—low, high
Duration—low, high
Tim ing—low, h igh
Rate of change—average
The indices can then be used for state or regional stream classiication analyses.
7.5 INDICATOR ORGANISMS
As opposed to habitat or lows, an alternative approach commonly used is to identify certain spe-
cies that, by their presence, are indicators of a healthy aquatic system. Typically, however, it is not
an individual species that is used as an indicator, but groups or types of organisms, where within
each group the individual species can be used as a metric, such as the percentage of occurrence.
An example may be the percentage of a species such as Achnanthes minutissima (a diatom spe-
cies) or groups of species (e.g., a number of Ephemeroptera/Plecoptera/Trichoptera [EPT] taxa).
Some of the more commonly used indicators include ish, aquatic algae, plants (e.g., periphyton
and macrophytes), and invertebrates. Mammals, reptiles and amphibians, birds, woody or wetland
plants, and other organisms may also be used. While there are many rare or endangered species,
it is usually the more common species that are preferable indicators, since they are easier to ind
and monitor. That is, rare and endangered species should be monitored, but probably not for this
speciic purpose. The considerations for the selection and sampling of indicators include their level
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