Environmental Engineering Reference
In-Depth Information
impact on wetland condition (Bradshaw et al.
2006
). Given that the decision to
invest in restoration is likely to be a socio-political one, it is more than likely
that few would advocate the pursuit of a pre-agricultural baseline as a target
for restoration. Perhaps we consider that, somewhere along this continuum,
humans moved from being part of the 'natural' environment to being external
agents of degradation.
Certainly wetlands change due to drivers other than industrial development.
Before industrialisation, the condition of wetlands varied with changes in
climate that are both cyclical and episodic. There is clear evidence in southeast
Australia of a sustained period of drying over the last few centuries (Jones et al.
2001
), and this has led to the lowering and evapoconcentration of these crater
lakes. Much of this change cannot be attributed to modern industry. More
recent, accelerated climate change (IPCC
2001
) is driven by industrial emis-
sions. These changes are influencing the present water balance in rivers and
lakes, and scenarios of future change are likely to shift the ecological character
of wetlands further. The MDB is within a climate change hotspot (Giorgi
2006
)
with modelled rainfall reductions higher than most parts of the globe. The
realisation of flow reduction scenarios ( Jones et al.
2002b
) on MDB wetlands
will make identified natural ecological character conditions unrealistic as
management targets. While catchment change appears to have been a stronger
influence on wetland condition to date (Gell et al.
2007a
), continued drying
across the southern MDB will aggravate the catchment drivers, heightening
the restoration challenge.
Conclusion
The use of diatoms and other complementary biological and chemical indi-
cators archived in sediment sequences provides an understanding of the pre-
impact condition of a wetland unavailable by other means. They can also aid
in the identification of drivers of wetland change and flag improvements in
condition. These approaches can be successfully applied to understanding the
long-term changes in condition of flowing waters provided neighbouring sites
of sediment accumulation exist and assumptions of the degree of exchange
between channel and wetland are acknowledged.
For restoration, there are many examples where managers have been mis-
directed in terms of identifying the driver of change, the means to ameliorate
impact and the target condition or restoration goal. The risk of undertaking
'restorative' measures without the knowledge often available in sediment
sequences is that the action itself becomes a driver of change, with the risk
that it combines with other drivers to direct wetlands into unprecedented
states. In these circumstances the managers lose contact with a previous
baseline and can merely claim to be constructing an artificial water body and
aquatic system. They then violate the core principals of frameworks or
