Environmental Engineering Reference
In-Depth Information
formed naturally between sequences of ridges that owed their origins to
coastal dune fronts associated with sea level high stands of each interglacial
over the last 700 000 years (Schwebel
1983
). These dunes, that ran parallel to
the coastline, hindered drainage of the interdune swales during wet winters.
From the mid 1800s, the government commissioned a drainage scheme to allow
pasture to be grown throughout the year on what were to become defined as
'seasonal wetlands'. While these wetlands inevitably dried as a consequence,
those at the coast that received the drainage water became fresh. Owing to the
early timing of the commencement of the diversion, these wetlands were widely
recognised as naturally fresh. The fossil diatom record, however, clearly demon-
strated a shallow, brackish baseline condition for several thousands of years
prior to drain construction (Haynes et al.
2007
). In this instance then, drainage
development, intended to stimulate the local primary industry, led to the pollu-
tion of naturally brackish water wetland, not with salt, but with freshwater.
Acidity/alkalinity
One of the most striking impacts of industry on natural systems is in the
release of heavy-metal pollutants to streams as acid mine drainage (AMD).
Upstream and downstream monitoring is usually sufficient to demonstrate,
spatially, chemical change to the receiving water and the consequent impact
on aquatic biota (e.g., Ferris et al.
2002
). Where the agent of change is more
diffuse, it is more difficult to identify the driver. The pH of several lowland MDB
rivers has been recognised as declining over recent decades. It is uncertain
whether this is due to changing rates of chemical leaching across agricultural
land, increases in multiple point source inputs or merely a function of impro-
ved instrumentation in recent times, also noted as a limitation of instrumental
data across Europe by Bennion and Battarbee (
2007
). Reid et al.(
2002
) sought
to test this by undertaking palaeolimnological analyses of wetlands along the
Goulburn River, a large tributary of the Murray River in Victoria. The diatom-
inferred pH showed great stability, at
6.5, for most of the 3000 years before
industrialisation, but species shifts after settlement illustrated a sustained shift
to pH
7.5. They attributed this increase in alkalinity to an increased transport
of base cations through erosion, increased groundwater input due to hydrolo-
gical imbalance after vegetation clearance or a reduction in humic acid input
through loss of vegetation cover. These explanations point to land clearance for
extensive agriculture; however, irrigation agriculture could be implicated if
the regulation of the river has reduced the exchange between the river and the
wetland allowing the river and the wetland to diverge chemically over time.
One of the more sinister impacts of extensive agricultural industry across the
MDB is the very recent outbreak of wetland acidification in riparian contexts.
Subsequent to its induced salinisation in 2000, under the shadow of an
extended drought, the pH of Psyche Bend Lagoon slipped from 9.5 to 5.1 across
