LaMotte 1097 User Manual

BOT TOM SAM PLING DREDGE

L

Mott

CODE 1097

IN TRO DUC TION

The LaMotte Bottom Sampling Dredge, a modification of the well-known
Peterson dredge, provides a convenient method for collecting bottom
sediments. It is used for collecting bottom sediments which may contain
mud, sand, ooze, and gravel; however, it is not designed to collect samples
from rock bottoms. By using a bottom sampling dredge, a number of
different analyses can be made. Since the bottom sediments represent a
good area to find macroinvertebrates and benthic algae, the communities
of organisms living on or in the bottom can be easily studied
quantitatively and qualitatively. A chemical analysis of the bottom
sediments can be conducted to determine what chemicals are available to
the organisms living in the bottom habitat. Also, the structural
characteristics of the bottom may be examined and related to the
biological and chemical analysis. All of these different studies are made
possible through the use of a bottom sampling dredge.

Whenever samples of the bottom are taken, every effort must be made to
insure that the samples are truly representative of the whole area. Much of
this depends upon the judgment of the individual taking the sample and
their individual study objectives. Ordinarily, take as many samples as
practical, since one sample has no value statistically. The time interval
between sampling and analysis is not critical for a mechanical or physical
analysis, but analysis is recommended for both biological and chemical
examinations.

IN STRUC TIONS FOR USE

The Bottom Sampling Dredge is shipped completely assembled. The
dredge has a bridle that reaches between the tips of the stainless steel arms
of the dredge. A line should be securely attached to the middle of the
bridle to retrieve the dredge from the bottom. When the dredge is lifted by
the bridle, the jaws of the dredge draw shut. When the arms are pushed
apart, the jaws of the dredge open. A rocking trigger mechanism attached
to the arms holds the dredge open. Holes in the upper part of the
collection chamber let air escape from inside the chamber as it is lowered
through the water.

1. Push arms apart, opening the dredge. Raise the rounded end of the
locking trigger mechanism and place tension on the retrieving line,
raising the dredge arms until the trigger catches in the notch on one
of the arms. The dredge will remain open as long as tension is
maintained on the bridle.

2. Lower the dredge through the water, keeping tension on the
retrieving line, until the dredge contacts the bottom.