Environmental Engineering Reference
In-Depth Information
Methods
Over the past decade, over 40 floodplain wetlands within the MDB have been
cored for palaeolimnological research (Barnett
1994
; Thoms et al.
1999
; Ogden
2000
; Reid et al.
2002
; Gell et al.
2005a
,
b
,
2006
,
2007b
, unpublished data; Fluin
et al.
2007
). Here, the records from a range of wetlands across the basin are
discussed from its middle to upper reaches nearer the Australian alpine region
to the Coorong at the mouth of the River Murray. The sites outside the MDB are
in coastal contexts that reveal the impact of water diversions. All wetlands are
selected to reveal wetland sedimentation rates and to demonstrate the use of
microfossil indicators to reveal changes to river and wetland condition. In
all sites, a Russian (d-section) corer (after Jowsey
1966
) was used to retain the
depth/age profile but often a field piston corer (after Chambers & Cameron
2001
) was used to increase sediment volume for analysis. In several wetlands,
cores were taken from 2 or 3, and in the Coorong 30, locations. At most sites,
samples were taken for
14
C AMS dating. Elsewhere samples were taken for
luminescence dating. In most instances, recent samples were taken for alpha
and gamma spectrometry to generate a
210
Pb decay profile and to gain evidence
for
137
Cs activity. The upper sediments of most cores were subsampled to
identify the arrival of exotic Pinus pollen (after Ogden
1996
). The changing
nature of the sediments in many cores was analysed utilising magnetic suscep-
tibility analysis by passing unopened PVC cores through a Bartington BS2 loop.
Subsamples were collected from all cores to extract fossil diatom algae to
reconstruct changes in wetland condition according to the known preferences
of species for salinity, pH and nutrients. Samples were prepared and enumer-
ated using standard methods (after Battarbee et al.
2001
). Species identification
was supported by reference to Krammer and Lange-Bertalot (
1986
,
1988
,
1991a
, b) and Witkowski et al.(
2001
). The ecological inferences from each
species are based on Van Dam et al.(
1994
), Gell (
1997
), Sonneman et al.(
2000
),
Gell et al.(
2002
), Tibby (
2004
) and Tibby and Reid (
2004
). The timing of increases
in river plankton in wetlands closely linked to the main channel is used to aid
the identification of the onset of river regulation in the mid 1920s.
A network of 25 cores along five, equally spaced shore-to-shore transects
were collected by Engstrom and co-workers from Lakes Pepin and St Croix in
1995 1996. Cores were taken with portable piston and Livingstone corers to
depths of 3.5 to 4.0m. The magnetic susceptibility of all cores was determined
across 2-cm intervals with a Bartington core logging sensor. Dry density data
were gained from loss-on-ignition techniques at 100
C, 550
C and 1000
C.
Small pieces of sub-fossil terrestrial woody material were sieved from selected
cores for
14
C dating using AMS. There were 20 sediment cores from Lake Pepin
that were analysed for
137
Cs and 10 for
210
Pb. In addition, 20 sediment cores
were analysed for total phosphorous (Engstrom et al.
2009
). Samples from
five of these cores were prepared for pollen analysis to assist with chronology,
