MYALL LAKES
The trophic history of Myall Lakes, New South Wales,
Australia: interpretations using d
13
C and d
15
N
of the sedimentary record
Simon Drew Æ Iona Flett Æ Joanne Wilson Æ
Henk Heijnis Æ C. Gregory Skilbeck
Ó Springer Science+Business Media B.V. 2008
Abstract In an attempt to determine the trophic
history of the Myall Lakes complex (New South
Wales, Australia) d
13
C
org
, d
15
N and C
org
:N profiles
were determined for bulk organic matter of two short
sediment cores from Bombah Broadwater and Myall
Lake.
210
Pb profiles and sediment types indicate
significantly different trophic trajectories during the
time periods examined. d
13
C
org
and C
org
:N indicate
Bombah Broadwater has been dominated by
increasing inputs of terrestrial organic material
over the last century, thought to be related to
watershed disturbance including agricultural activ-
ity. Primary production appears to be dominated by
phytoplankton. d
15
N remained relatively stable at
around 1% until the mid–1970s when there was a
sharp increase to 4.7%, interpreted as an influx of
sewage-derived material. These observations offer
an insight into the recent trophic changes at the
site. Sedimentation rates are noticeably lower in
Myall Lake and the most recent sediment is a
flocculent organic rich deposit overlying mineral
clay. d
13
C
org
and C
org
:N values indicate a transition
from plankton to macrophyte dominated primary
production around 1800AD. d
15
N values become
increasingly negative from approximately 1900AD.
This is interpreted as being due to increasing
reliance by macrophytes on nitrogen recycled from
decomposing sediments driven by natural infilling
and eutrophication in this basin. The contrasting
sedimentation rates, sediment types and geochem-
ical profiles suggest the different basins of this
water body are subject to substantially different
internal and external influences which should be
considered in management decisions.
Keywords Sediment Á Lakes Á Isotopes Á
Trophic Á Carbon Á Nitrogen
Guest editors: J. Wilson, L. Bowling & J. Tibby
The Myall Lakes: patterns and processes in an unusual coastal
lake system in eastern Australia
S. Drew (&)
School of Geography, Politics and Sociology, University
of Newcastle upon Tyne, Newcastle upon Tyne, UK
e-mail: S.Drew@newcastle.ac.uk
I. Flett
Department of Archaeology and Natural History,
Research School of Pacific and Asian Studies, Australian
National University, Canberra, Australia
Present Address:
J. Wilson
The Nature Conservancy - Coral Triangle Center, Sanur
80228, Bali, Indonesia
J. Wilson
Centre for Natural Resources, NSW Department of
Infrastructure, Planning and Natural Resources,
493 Hunter St., Newcastle, NSW 2300, Australia
H. Heijnis Á C. G. Skilbeck
Department of Environmental Sciences, University of
Technology, Sydney, Australia
123
Hydrobiologia (2008) 608:35–47
DOI 10.1007/s10750-008-9383-3