Environmental Engineering Reference
In-Depth Information
2.2.4 Sediment traps
monitored, however, and in this situation the impact
of zooplankton activity, solubilisation of collected
material as well as problems with hydrodynamics
(water flow across the trap mouth) all need to be
considered if the sediment traps are to be used quan-
titatively (Buesseler et al ., 2007).
Sediment traps have been used in lakes for both
short-term and long-term studies. Sigee et al . (2007)
employed traps over a relatively short (9 days) period
in their studies on cell death during late-season bloom
decline in a eutrophic lake. Sedimenting phytoplank-
ton was sampled in sediment traps (1-l plastic bot-
tles with entry funnels) at a depth of 4 m. Bottles
were filled with sterile water before gently lower-
ing to the required depth to prevent filling with lake
water and contamination with suspended phytoplank-
ton. Sediment traps were left in the water column for
successive periods of 3 days during mid-November.
At this late stage in the season, the sedimenting
phytoplankton is dominated by resistant spores of
algae such as Ceratium and Anabaena ,withalot
of organic debris derived from decomposing vegeta-
tive cells (Fig. 2.7). Longer-term studies have been
carried out to investigate seasonal changes in lake
sedimentation. Livingstone and Reynolds (1981), for
example, monitored seasonal changes over a 1.5-
year period, emptying traps at approximately three
Sediment traps have been widely used in fresh water
biology to monitor particle fluxes at the top of the
water column of standing waters. The traps are typi-
cally suspended from a fixed buoy and are positioned
in the lower part (or just below) of the epilimnion for
a fixed length of time to collect algae that are sedi-
menting out of the major productive region (euphotic
zone) of the lake. In addition to sedimenting phyto-
plankton, the traps will also collect organic and inor-
ganic particulates deposited onto the lake's surface
and sediment that has become re-suspended during a
period of lake turbulence.
The traps typically consist of an open bottle, with
a top funnel that directs sedimenting phytoplankton
and other material into the bottle chamber. In some
aquatic studies (particularly oceanographic projects)
sediment traps may be left for a long period of
time (weeks to months). These traps may have mul-
tiple collectors that cycle through time to record
seasonal changes in algae. Over long time periods,
where algal populations are simply being enumer-
ated,chemicalpreservationofmaterialisnecessaryto
prevent algal decomposition and zooplankton inges-
tion of material within the trap. Chemical preserva-
tion cannot be used where nutrient cycling is being
org
d
e
25 μm
10 μm
Figure 2.7 Lake sediment trap collection. Examples of late-season sedimented material, dominated by spores of algae
such as (left) Ceratium hirundinella (SEM image) and (right) Anabaena (light microscope image). A group of spores
(akinetes) of Anabaena are associated with organic debris (org) and appear to be either viable (d, dense contents) or
non-viable (e, empty). The spores of these algae can be compared with actively growing vegetative cells - Figs. 4.56 and
4.24, respectively.
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