Page 8 - IJMS 878-Vol.3 No.41

International Journal of Marine Science 2013, Vol.3, No.41, 333-343
http://ijms.sophiapublisher.com
334
turbulence and thus sediment re-suspension through
mixing of the water column. The effects of sediment
re-suspension are likely to be marked in this lake due
to the presence of the NH4-rich sediment “gyttja”,
fine sediment which would presumably be particularly
susceptible to re-suspension. Since the species
composition of the phytoplankton in this lake are well
understood, this lake would provide an ideal
opportunity to determine the ways in which mixing of
the water column and sediment re-suspension will
affect the phytoplankton communities.
The present study deployed artificial mesocosms
within a location in Myall Lakes to determine the
effect of re-suspension of gyttja on phytoplankton cell
abundance and species composition and to understand
the relationship between water quality parameters and
the abundance and composition of phytoplankton
following a mixing event. The hypothesis tested in
this study is that gyttja mixing directly introduces
benthic microalgae into the water column, thereby
altering the species composition of phytoplankton, (2)
raised levels of NH4 produced by gyttja mixing
stimulate growth of certain phytoplankton at different
rates, and (3) the combination of the above will result
in marked changes in the phytoplankton communities.
2 Materials and Methods
2.1 Study site
The study was carried out at Neranie Bay, which lies
at the most northern part of the Myall Lake system in
central NSW, Australia (Figure 1). This lake system is
Figure 1 Location of study in Myall Lake on the Coast of NSW
typically <2 m in water depth and is supplied by the
Myall River, in which the lower regions can be up to 8
m in depth (Atkinson et al., 1981). Although Myall
Lake and the lower reaches of Myall River are subject
to some tidal influence, fluctuations of average water
depth 2.8 m are mainly attributed to the seasonal
rainfall in this area (Thorn, 1965).
2.2 Mesocosms and sampling procedure
The study used 6 purpose-built mesocosms, which
incorporated pieces of transparent; polycarbonate
sheeting that were joined together with lengths of
timber and wood screws (Figure 2). The circumference
of each mesocosm was 3.1 m and the diameter was
approximately 1 m.
Figure 2 Experimental mesocosm: A: water sample collection,
and B: structure and dimensions of the mesocosms (polycarbonate
sheeting with wood framing) (from Sampaklis, 2003)
An in situ experiment was carried out between 6th and
13th February 2003 at Neranie Bay, which consisted of
3 control (CM) and 3 impacted (IM) mesocosms and a
further three replicate (C) sites located outside but
nearby to the mesocosms. All sites were located in
areas that contained extensive areas of gyttja.
Water samples (containing phytoplankton) were
collected from the water column using a PVC pipe
with a U-pipe adaptor at six sites just prior to the
installation of the mesocosms. At the same time, three
water samples were collected from three sites nearby.
Within 1 hour of placing the mesocosms, the top 20
cm of gyttja in the IM was manually mixed using a
garden rake (termed disturbance) for a 5 min period of
mixing. Water samples were collected using the PVC
pipe and U-pipe adaptor from all nine sites at time
intervals of 30 min, 3 h and 1, 2, 3, 4 and 5 days
following the disturbance.
From each sample, water quality (DO, Temperature,
pH and salinity) was measured and 30 ml water
samples for available nutrients (orthophosphate, NOx,