Environmental Engineering Reference
In-Depth Information
so they may not be representative. In addition, some criteria, such as the extent and percentage of
cover, may not relect the impacts due to species composition, such as that of invasive species.
15.3.2.3 Neuston
The neuston refers to organisms that live in the upper water surface ilm or surface microlayer. The
term neuston was introduced by Naumann (1917) to designate the community of organisms associ-
ated with that surface microlayer. The neuston are typically subdivided into the epineuston, which are
attached to the top of the surface, and the hyponeuston, which are attached to the bottom of the sur-
face. They may also include some organisms that move over the surface ilm (Thorp and Covich 2010).
Organisms of the neuston include bacteria, protozoans, insects such as whirligig beetles and
water striders, some spiders, and others. The neuston is known to accumulate nutrients and the base
of the food chain is typically the layers of organic materials, such as lipids, lipoproteins, and poly-
saccharides (Bolsenda and Herdendorf 1993, Maier et al. 2009).
The neuston live on the water surface and are associated with the surface tension of water, so
organisms such as Cyanobacteria, which rise to the surface because of their gas vacuoles, are excluded
from this group. Some organisms spend only part of their life cycle in this surface microlayer.
15.3.2.4 Benthos
The benthos are the bottom dwellers. The characteristics of the benthos depend largely on the lake
region (littoral zone, profundal) in which they live. In terms of the distribution of bottom-dwelling
organisms, Cole (1979) further subdivides the benthos into the phytobenthos and the zoobenthos.
The phytobenthos is comprised of the periphyton and macrophytes, which were discussed earlier,
so this section will focus on the zoobenthos.
The zoobenthos represent a diverse assemblage of organisms, one of the more important of
which is the insects (SWCSMH 2006):
The freshwater world has more than 500,000 different species of insects. They occur in habitats that
range from hot springs, discarded tin cans, temporary ponds, spring seeps, wetlands, rivers, lakes, to
arctic and mountain pools. In fact, if water will stand for a few days, one or another of the ubiquitous
chironomids will probably be the irst to inhabit that water “… Take a walk down to the lake. It does not
matter what time it is—there will be insect activity somewhere! (Narf 1997)
The type and biomass of zoobenthos depend on factors such as the substrate (e.g., gravel, sand, and
silt), the organic content, etc., which impact their abundance and diversity, as illustrated in Table 15.4.
The zoobenthos may be attached to the bottom, burrow in it, or be associated with aquatic plants.
TABLE 15.4
Abundance and Species Diversity of Aquatic Insects Found in Five Habitats (Characterized
Mainly by Their Substrates) in a Quebec Stream
Habitat
Abundance (no. m -2 )
No. of Species
Diversity = (S - 1)/log e N
Sand
920
61
1.96
Gravel
1300
82
2.31
Cobbles and pebbles
2130
76
2.02
Leaves
3480
92
2.40
Detritus (inely divided leaf material in pools
and along stream margins)
5680
66
1.73
Source: SWCSMH, Chapter 1: Zoobenthos of Freshwaters—An Introduction, Soil & Water Conservation Society of Metro
Halifax, 2006, Available at http://lakes.chebucto.org/ZOOBENTH/BENTHOS/i.html, accessed February 8, 2012.
Note: Values are annual averages.
 
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