Environmental Engineering Reference
In-Depth Information
were limited through regulation. Through the drought of 2001 2009, the salinity
of the Coorong increased to over 100 mg L
1
and declines in fish and migratory
wader communities were well-documented. The lagoon was identified as a site
deserving of River Murray environmental flows, and there were widespread
calls through the media to release water under the National Water Initiative to
arrest the ecological decline. Sediment-based analyses of diatoms (Fluin et al.
2007
) identified salinity, but more so turbidity as the causative agent of the
decline of Ruppia, the keystone autotroph in the natural system. Critically,
it identified that the system was naturally sub-saline with salinities typically
5 35mg L
1
, and it was a clear water, strongly tidal system that had little direct
link with the River Murray over the 7000 years of its existence. Also, its decline
commenced several decades before its Ramsar listing, and this was attributable
to the closing of the Murray mouth due to reduced flows and reduced fresh-
water inputs from the hinterland. Complementary analysis of carbon and
nitrogen isotopes (Krull et al.
2009
) revealed that the elevated salinities, regu-
lated to maintain a 1985 baseline, had caused a collapse in the decomposer
flora leading to a net increase in sediment carbon inducing anoxia at the
sediment-water interface. This led to the production of sulphides that are
potentially toxic to Ruppia (Heijs et al.
2000
). So in this instance, the manipu-
lation of flows from the hinterland and the reduction of flows through the
MDB, both to consequences of water manipulation to serve agricultural indus-
tries, drove a collapse in the wetland ecosystem, exacerbated by policy driven
by a short-term understanding of baseline condition.
In acute cases of water management intervention, the salinisation of a
wetland can be directly attributed to a cause, particularly if the site is being
monitored regularly. In the case of Psyche Bend Lagoon near Mildura in the
MDB the wetland was measured to be 1 2mg L
1
for several seasons before it
rapidly increased in salinity to over 50mg L
1
within 1 year. This was attribut-
able to a management decision to divert irrigation return flows away from the
wetland with the intention of reducing salt flux to the main river channel,
the principal source of water for irrigators. The catchment manager defended
this as allowing the lagoon to play its role in the system implying that Psyche
Bend Lagoon was naturally hypersaline. The monitoring data over this time
frame (Gell et al.
2002
) provided sufficient evidence, supported by evidence of
dead trees and freshwater Cyperus roots around the lagoon margins, for a fresh
to oligosaline baseline condition. This was denied for the purpose of pragmatic
management purposes that ultimately represent an injustice to the natural
system (Gell
2007
). This trade-off may be a portent of the effect of the more
official implementation of the derogation clause under the WFD.
The necessary corollary of the impact of water diversions on increasing
wetland salinity is that the receiving waters may be freshened. This is the case
for the coastal wetlands in the southeast of South Australia. Here, wetlands
