Geoscience Reference
In-Depth Information
Zoobenthos, benthic algae and macrophytes
- Size criteria: macro-, meso- and meio-benthos
- Feeding criteria:
Shredders
Collectors
Scrapers
Predators
Filter Feeders
Benthic
algae
Substrate
Epiphytic
(grows on plants
or animals)
Epipelic
(grows on/in
sediments)
Epilithic
(grows on
rocks/stones)
Periphyton
(grows on artificial
substrates, e.g. boats)
Littoral zone;
litt
oral sediments
Water surface
Pelagic zone;
profundal sediments
Macrophytes
- Free-floating
- Permanent stands, e.g.
(1) emergent with green
parts above the water
surface,
(2) floating-leaved, or
(3) submerged, with all parts
below the water surface
Thermocline
Fig. 4.5
Compilation of concepts
related to sediment-living organisms
(zoobenthos, benthic algae and
macrophytes) (see also Vollenweider
1968, 1976; Cummings 1973;
Brinkhurst 1974; Wetzel 2001).
2
Areas of transportation (T) prevail where
fine materials are deposited periodically (areas
of mixed sediments). This bottom type generally
dominates where wind/wave action regulates
the bottom dynamic conditions (see Fig. 4.6).
It is sometimes difficult in practice to separate
areas of erosion from areas of transportation.
3
Areas of accumulation (A) prevail where
the fine materials are deposited continuously
(soft bottom areas). Owing to their fine-grained
nature these are the areas (the 'end stations')
where high concentrations of pollutants may
appear (see Table 4.5).
The water content, grain size and/or the com-
position of the material are often used as cri-
teria to distinguish different sediment types (see
Table 4.5; or Sly 1978). From the basic Stokes'
equation for settling particles (see Chapter 1),
as well as for convenience, the limit between
coarse and fine materials can be set at a particle
size of medium silt (0.06 mm). The generally
sandy sediments within the areas of erosion and
transport (ET) often have a low water content,
low organic content and low concentrations
of nutrients, low benthic biomass and few
contaminants (see Table 4.5 and Fig. 4.7). The
conditions within the T areas are, for natural
reasons, variable, especially for the most mobile
substances, such as phosphorus, manganese
and iron, which may react rapidly to alterations
in the sediment chemical 'climate' (as given
e.g. by the redox potential). Fine materials may
be deposited for long periods during stagnant
weather conditions. In connection with a storm
or a mass movement on a slope, this material
may be resuspended and transported, generally
in the direction towards the A areas in the deeper
parts, where continuous deposition occurs. Thus,
