FACTSHEET ON WATER QUALITY PARAMETERS
Macroinvertebrates
Macroinvertebrates are small organisms without a backbone that are visible to the naked eye and large enough to be
easily collected. Analyzing the macroinvertebrates in a waterbody can heip recognize signs of ecosystem health.
Why do we measure macroinvertebrate communities?
Insects are the most common macroinvertebrates in
aquatic systems, iiving in water as nymphs or larvae at
least until they reach their adult stages. Common insects
in aquatic systems include dragonflys, caddisflies,
stoneflies, beetles, midges, and mayflies. Others, such as
aquatic worms, leeches, and small crustaceans (crayfish
and fairy shrimp), live entirely in water. Most species live
in the bottom sediments of the waterbody or attached
to rocks, vegetation, logs, and sticks. Lifespans range
from a few weeks to several years. Macroinvertebrates
are most frequently used for biological monitoring, or
"biomonitoring," because of their prevalence in aquatic
habitats and their differing sensitivities to chemical
pollution and physical disturbances. Biomonitoring is
the use of organisms to assess the overall quality of
their environment or habitat. Because they generally
have limited mobility and cannot escape pollution,
macroinvertebrates better reflect the long-term water
quality of a site compared to a single sample of chemical
constituents that only provides a snapshot in time. Tabie
1 shows examples of generalized pollution sensitivity
(tolerant or intolerant of pollution) for several common
macroinvertebrates.
Table 1. Examples of macroinvertebrates and their pollution
sensitivity levels.
Macroinvertebrate Poiiution Sensitivity
Stonefly
Intolerant
Mayfly
Intolerant
Crayfish
Moderately Tolerant
Leech
Tolerant
Aquatic worm
Tolerant
Knowing the typical variety and abundance of
macroinvertebrates in a healthy waterbody in a region can
help indicate signs of poor ecosystem health. Generally,
healthy waterbodies support a diverse population of
macroinvertebrates. Samples yielding only pollution
tolerant species, a low abundance of organisms, or very
little diversity (primarily one or two species) might
indicate a degraded waterbody. Figure 1 shows an
example of a mayfly, a type of pollution sensitive
macroinvertebrate.
Source: Maine Department of Education (Nd)
Figure 7. The mayfly, a type of insect, under the view of a
microscope. Credit: Photo courtesy of USGS
An assessment of macroinvertebrates heips to determine
whether a stream's designated uses related to aquatic life
are supported (protection and propagation offish, shellfish,
and wildlife). Unlike other parameters, macroinvertebrates
offer a direct measurement of the condition of the
biological community within a waterbody.
For factsheets on other water quality parameters, visit:
epa.qov/awma/factsheets-water-qualitv-para meters.
For more information about the CWA Section 106 Grants Program, visit:
epa.qov/water-pollution-control-section-106-g rants.

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Macroinvertebrates
What affects macroinvertebrate communities?
Several factors, including streamflow, geology, elevation,
temperature, dissolved oxygen, seasonal life cycle patterns,
substrate, and riparian habitat influence the abundance
and diversity of macroinvertebrates in a waterbody.
Human-induced changes to aquatic ecosystems can
include increased pollution (from urban runoff and point
source discharges) and land use changes that alter natural
streamflow patterns, modify the channel structure, or
contribute to nonpoint source loadings to the waterbody.
Below are some examples of the effects of human-induced changes on macroinvertebrate communities:
Increased turbidity and
sedimentation in the waterbody
from reduced riparian
vegetation or other causes
of erosion can eliminate
food sources and habitat for
macroinvertebrates.
Excess nutrients can
promote algal blooms.
The eventual death and
decomposition of the
excessive algae depletes
dissolved oxygen, reducing
macroinvertebrate survival.
Increased concentrations of
metals, pesticides, or other
toxic pollutants can shift
the relative abundances of
macroinvertebrates toward
more pollution tolerant
species.
Altered pH affects
macroinvertebrate survival
by weakening shells and
exoskeletons (if pH is
decreased) or reducing the
survival of alkaline-intolerant
species (if pH is increased).
What are EPA's recommended criteria for macroinvertebrates?
There are no published EPA recommended water quality
criteria for macroinvertebrates. However, guidance
materials are available to help develop biological
criteria that define specific characteristics of healthy
macroinvertebrate, fish, or algal communities. A useful
example of an approach to setting targets is EPA's A
Practitioner's Guide to the Biological Condition Gradient:
A Framework to Describe Incremental Change in Aquatic
Ecosystems (2016).
A multimetric index approach can be used to set
targets for biological criteria. A macroinvertebrate
multimetric index (MMI) is a numerical value calculated
by combining individual measurements (metrics) of the
macroinvertebrate community in a sample into an overall
index score. This score is intended to reflect the overall
condition of the macroinvertebrate community. There are
often different indices and thresholds for different regions
and waterbody types.
How do we measure macroinvertebrate communities?
Macroinvertebrate samples are collected in the field and
identified in the laboratory (Figure 2 and Figure 3). An MMI
used to characterize samples may include abundance,
richness (number of species present), composition
(proportions of species), number of pollution-sensitive
species, or other measurements appropriate for the
program's data analysis and assessment methods.
There are many examples of the development and use
of macroinvertebrate indices by states, tribes and other
agencies including EPA's National Aquatic Resource
Surveys. This work can be leveraged as ecoregional
indices/MMIs to be used along with their protocols.
Sampling locations and times
Sampling locations can be selected using a targeted
design or random design. For example, river or stream
sampling sites may be located in riffles (shallow, turbulent
sections of a river) or runs (smooth-flowing sections of a
river) to represent the range of macroinvertebrate habitats.
Samples are typically collected by moving upstream
to prevent disturbance. Sampling times, seasons, and
frequencies should be determined by the life cycles of the
macroinvertebrate species as appropriate.
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Macroinvertebrates
Figure 2. Using D-frame and kick net to collect
macroinvertebrates. Credit: Photo courtesy of USEPA
Equipment and methods
Macroinvertebrate sampling requires little equipment, with
methods depending on the waterbody being sampled. For
example, nets such as the D-frame and kick net (Figure 2)
are typically used in streams. After sampling, samples are
sorted and identification is done visually. A microscope
can be connected to a screen to provide higher quality
lighting and magnification (Figure 3). Unless the data are
for educational purposes, it is strongly encouraged that the
samples be reviewed by a trained taxonomist, which may
be a staff member or an outside expert.
Other parameters measured at the same time
Macroinvertebrates are the most commonly measured
organism group for biological assessments, followed by
fish and periphyton (organisms such as algae that attach
to objects in waterbodies). Measurements of basic water
quality parameters (pt I, temperature, turbidity, dissolved
oxygen [DO], nutrients) taken during sampling will give
a more complete picture of the overall status of the
waterbody.
Figure 3. Using a microscope to identify macroinvertebrates.
Credit: Photo courtesy of USGS
What are the challenges of using macroinvertebrates as a water quality
parameter?
Some of the genera! challenges in macroinvertebrate
sampling include ensuring consistency among staff when
collecting samples, taking appropriate sample sizes, and
conducting adequate research to understand and interpret
results. Specific considerations include the following:
Because some macroinvertebrates are small and fast-
moving, adequate training is needed to coiiect them.
Findings can vary based on the method used, sample
size collected, and taxonomic level used. Thus, it may
not be appropriate to average or otherwise combine
data from multiple macroinvertebrate samples when
assessing waterbody health.
Because macroinvertebrates are affected by
multiple pollutants, using them to identify or track
a specific pollutant of concern is challenging. Also,
macroinvertebrates do not respond to all types of
pollutants. For more information, see EPA's Stressor
Identification Guidance Document (2000).
Because macroinvertebrates are affected by
multiple natural factors such as temperature and
streamflow, the absence or presence of certain
macroinvertebrates does not necessarily indicate poor
or healthy water quality. This information should be
considered along with other indicators of long-term
water quality characteristics.
EPA 841F21007E | July 2021
oEPA

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