Environmental Engineering Reference
In-Depth Information
forest, while the scrappers (Elmidae, Dryopidae) and predators
(Rhyacophilidae, Agrionidae) the pine-oak forest. Trichoptera is abundant
in the forest as well as forest-agriculture land use. They functioned as
shredders, collectors and gatherers in the former, whereas collectors, gather-
ers, fi lterers in the forest-agriculture land use. Scrapers (mainly
Ephemeroptera) occurred in very low percentage in the forest-agriculture
land use. Slope is observed to be an important environmental variable
infl uencing taxonomic composition and distribution of caddisfl y with case
(Limnephilidae, Leptoceridae, Philopotamidae) along with mayfl y
(Leptophlebiidae, Baetidae) and stonefl y (Perlodidae). As slope is a
manifestation of altitude, it indirectly indicates the role of altitude and
hence the forest.
Keywords
Forest type • Himalaya • Ordination techniques • Slope • Trichoptera
Introduction
utes, detritus, sediments and organisms are con-
stantly delivered from upstream to downstream
areas. Odum (
1996
) is of the view that current
velocity is the major limiting factor in the lotic
environment. Thus streams generally exhibit two
major communities, rapids and pools; within
these broad categories the type of bottom whether
sand, pebbles, clay and bedrock determines the
nature of the communities and the population
density of community dominants. The biota of a
river channel resembles that of the rapids, except
the population distribution is highly “clumped”
owing to the frequent absence of fi rm substrates.
The feeding relationships and other interac-
tions form a complex whole often referred to as
the biological community. Community is usually
applied to a group of populations that occur
together, but there ends any similarity among
defi nitions. Ecologists also defi ne communities
on the basis of interactions among associated
populations. This is a functional rather than
descriptive use of the term. Community itself is
a wide term with various meanings, but essen-
tially it is used to denote a collection of species,
living together, and usually linked to a particular
habitat. Kendeigh (
1980
) considered community
or biocenose as an aggregate of organisms,
which form a distinct ecological unit. Association
Odum (
1996
) classifi ed organisms in water
according to their life form or life habit based on
their mode of life into the following:
1. Periphyton or Aufwuchs, the organisms (both
plant and animals) attached or clinging to
streams and leaves of rooted plants or other
surface projecting above the bottom.
2. Plankton, the free-fl oating microscopic organ-
isms of plant or animal origin, which remain
at the mercy of the current and associated with
water-water interface.
3. Benthos, the fl oral or faunal components that
dwell on the bottom or in the bottom sedi-
ments of the stream and are associated with
solid-water interface.
4. Neuston, the organisms associated with air-
water interface and resting or swimming on
the surface of water.
5. Nekton, the fauna associated with water-
water interface capable of performing active
locomotion as they have powerful locomotory
organs (e.g. fi shes).
The rivers are characterised by their unidirec-
tional fl ow and thoroughly mixed waters (Patrick
1948
). Cooper et al. (
1998
) state that streams are
characterised by a unidirectional fl ow, and sol-
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