Environmental Engineering Reference
In-Depth Information
presence is evident in sediment layers deposited earlier in the 500-year record,
this sharp, sustained rise in several halophilous taxa is clear evidence for
the impact of early primary industry development in the MDB. Downstream,
a diatom record from a levee lake widely considered to be in 'good ecological
condition', Loch Luna (
Fig. 8.2
), was revealed to have a natural 'baseline'
condition of clear, shallow water with occasional mudflats (Gell et al.
2007b
).
Again, the diatoms in the sediment deposited at the commencement of river
regulation showed that the commissioning of these flow control structures
stimulated a rapid increase in river plankton in the wetland. The reconstructed
salinity, based on a salt lake diatom transfer function (Gell
1997
), revealed
a sustained increase in salinity from that time, to a concentration ten times
the longer term, pre-industrial average. This site, by virtue of being amongst a
woodland of Eucalyptus camaldulensis, was protected from the early impacts
of primary industry activity, despite being within kilometres of early grazing
runs at Overland Corner. However, it has been impacted by the more diffuse
catchment changes as a consequence of its permanent link to the river channel
subsequent to regulation.
Salinity concentrations can rise in a wetland due to both the increased flux
of salts but also the reduction of freshwater supply that dilutes the incoming
salts and mediates the effects of evapoconcentration. Associated with the MDB
on account of the building of a major inter-basin transfer and hydroelectricity
facility termed the Snowy River Scheme, often considered one of the wonders
of the industrialised world, is the Snowy River. Its catchment remains largely
forested within national parks but, from 1966, 98% of its mean flow 'below
Jindabyne' (weir) was diverted inland to supplement water for irrigation within
the MDB and for HEP. At the end of the Snowy River in the floodplain,
MacGregor et al.(
2005
) revealed a fresh and perhaps dystrophic baseline condi-
tion for Lake Curlip. The diatom-inferred salinity increased after the develop-
ment of the coastal flats for cattle grazing in the late 1800s but a stepped
increase was noted abruptly after the commissioning of the Snowy Scheme.
Ultimately, the combined effect of local hydrological change and an inter-basin
transfer for primary and power production was a near 50-fold increase in
salinity from
0.5 to at least 20mg L
1
.
An additional MDB wetland impacted by abstraction and diversion is the
Coorong, a 120 km long coastal lagoon ending at the River Murray mouth
that developed behind a barrier dune system after the stabilisation of sea levels
7000 years ago. In 1985, it was listed as a wetland of international signifi-
cance under the Ramsar protocol and its ecological character was described
as a saline to hypersaline, reverse estuary (DEH 2000). This was, in fact, at odds
with the case made for a brackish system made evident though ethnohistoric
accounts (England
1993
), but the case, and the consequent obligations under
Ramsar, were influential and releases from the southeast of South Australia
