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Invertebrates
Benthic invertebrates are animals living in or on bottom sediments
of streams, rivers, lakes, or estuaries. Changes in benthic invertebrate
community structure (species composition and abundance) from a baseline
characterized before disturbance can be use to evaluate impacts
during the operational or closure phase of a mine. For abandoned
mines, a baseline for benthic invertebrate health may not be available
and assessment of environmental impact must be based on other indicators.
In these cases, reference areas with similar physical and chemical
conditions can be used to provide a baseline (e.g. an area upstream
of a discharge source). Because these invertebrates inhabit sediment
bottoms of streams, rivers and lakes, they are directly influenced
by mine related discharges thus, monitoring of changes in benthic
invertebrate community structure over time provides a good means
of detecting impacts due to mining. The study area chosen for monitoring
usually encompasses the region between the origin of a point source
discharge and the boundary where ambient water chemistry conditions
exist (i.e. were mine-related chemistry can no longer be reliably
detected). The number of sampling stations monitored is a function
of the size of the affected area and the amount of variability in
benthic community structure (i.e. variability in community depth,
sediment type, and species diversity) (MEND,
2001).
Stream and River Sampling
Generally, the preferred method for small stream sampling is to
use a net sampler. There are several varieties of net samplers,
of which Hess and Surber samplers are the most common. The net samplers
enclose or delineate a fixed area of substrate upstream of the net.
The net, constructed of mesh, is supported by a frame that directs
the bag in the direction of the flow. To operate, the samplers require
enough current to inflate the net. The net sampler is placed in
a randomly-selected location within the stream, with the net oriented
downstream. The substrate within the enclosed area is hand-stirred
for a fixed length of time (usually one to two minutes) to dislodge
invertebrates from the substrate where they are captured by the
net. The organisms are washed and/or picked from the collection
net and placed in sampling jars and preserved. The next sample is
collected from similar habitat at a randomly-selected location upstream
of any area previously sampled.
In large, fast flowing streams or rivers, collection of benthos
can be very difficult. Large artificial substrate traps filled with
clean, native substrate (rocks and stones) can be set by divers
and left to be colonized by invertebrates. Retrieval of the nets
requires that divers place mesh bags over the traps to prevent the
loss of organisms before the traps are raised to the surface. This
is a logistically difficult, costly, and risky means of monitoring
benthos in large rivers. Despite this, few other quantitative measures
exist for large rivers (MEND,
2001).
Lake and Estuary Sampling
The common method for collecting samples from lake and estuarine
habitats is to use a grab sampler. There are several different designs
of grab samplers, of which, the most common are Ponar, Petersen,
van Veen, and Ekman. All of the grab samplers operate in a similar
manner by capturing a know dimension of substrate. Typically a grab
sampler is operated from a boat, usually by hand, but sometimes
with a winch when conducting large grabs. The sampler is lowered
to the bottom at a speed not exceeding 0.5 m/sec and allowed to
penetrate the bottom substrate. It is important that the grab not
be lowered too quickly, such that organisms below the sampler cannot
detect the bow wave and possibly avoid capture. The grab is then
triggered (upon contact with the bottom) and then is slowly pulled
or winched back to the surface.
It is important that an intact, undisturbed sample is collected.
Rocks and twigs can prevent the jaws of the grab sampler from closing
completely causing leakage. Leakage can significantly bias sampling
results since different samples will be different sizes. Grab samples
should be sieved using a 180 to 250 mm mesh screen to remove fine
sediment particles and very small organisms. The samples should
then be preserved in the field using 10% formalin buffered with
Borax to a pH of at least 8.2. Sampling jars should be properly
labeled with the following information: date of sample collection,
location, and a unique sample station identifier (MEND,
2001).
Problem | Compliance
| Health & Safety | Sampling
| Analytical | Data
Quality
Site Assessment | Prediction
| Construction | GIS
| Monitoring & Assessment
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