potential-impacts-of-climate-change-on-the-swan-and-canning-rivers

levels may increase waterlogging, reduce the rate and extent <strong>of</strong> oxygen infi ltration and provide a
transient barrier to the production <strong>of</strong> acidity via sulfi de oxidation.
Agriculture is the predominant land use in the Avon Region. Increasing productivity on cereal farms
is resulting in increased yields despite a decline in rainfall. However, if plant and economic thresholds
are exceeded, <strong>change</strong>s to farm enterprises will result. A drier <strong>climate</strong> has been predicted to
result in further expansion <strong>of</strong> grain growing in the wetter, western parts <strong>of</strong> the Avon Catchment (e.g.
O’Conner et al. 2004) and a possible expansion <strong>of</strong> stock in the wheatbelt if drier seasons make
cereals too risky to grow (John et al. 2005). Some perennials may be harder to establish as the <strong>climate</strong>
dries. However, a shift to animal-based industries could encourage perennial fodder shrubs.
The key <strong>impacts</strong> <strong>of</strong> <strong>climate</strong> <strong>change</strong> in the broader catchment are summarised in Table 16:
Table 16 Anticipated future <strong>change</strong>s in the broader Avon Catchment
Area
Agriculture <strong>change</strong>
Water, sediment, nutrient,
carbon and salt loads
Vegetation
Impact <strong>of</strong> Climate Change
Drought and <strong>change</strong> in land practices
Reduced rainfall, flow, sedimentation, nutrient load and salt load
Demarcation between jarrah-marri and wandoo woodlands is
moving west
Change in fire regime and groundwater recharge, water discharge
and sedimentation
Acid Sulphate Soils
Wet habitats decreasing or are being lost
2.2 Impacts on Swan and Canning rivers
Exposure <strong>of</strong> peaty soils in low buffering conditions which leach
acid and mobilise heavy metals.
The <strong>impacts</strong> <strong>of</strong> <strong>climate</strong> <strong>change</strong> on the Swan and Canning rivers are discussed under the following
headings: ecological <strong>impacts</strong>; <strong>impacts</strong> on infrastructure; human health and social <strong>impacts</strong>; and economic
<strong>impacts</strong>. These subject areas are indicative <strong>of</strong> the priority management areas for the Swan
River Trust.
2.2.1 Impacts on ecology
The ecological system <strong>of</strong> the Swan and Canning rivers is diverse and subsequently the <strong>impacts</strong> <strong>of</strong>
<strong>climate</strong> <strong>change</strong> are numerous. Consequently, for ease <strong>of</strong> discussion, the <strong>impacts</strong> on ecology have
been broken into a number <strong>of</strong> sub-sections, namely: sediment composition and nutrient loads; dissolved
oxygen levels; nutrient cycling; fringing vegetation; community structure (including trophic
dynamics with a particular focus on birds and fi sh); mudfl ats; sea grass and macro-algae; biodiversity;
acidifi cation; and geomorphology.
Sediment composition and nutrient loads
Anticipated reductions in rainfall and increased atmospheric and riverine temperatures will impact
sediment retention and composition in the Swan Canning river system (as discussed above). Sediment
composition is affected directly by the deposition <strong>of</strong> particulate nutrients, sediments and organic
matter in river run<strong>of</strong>f, and indirectly by the effi ciency <strong>of</strong> trapping <strong>of</strong> dissolved nutrients in river
run<strong>of</strong>f by phytoplankton blooms – which subsequently deposit on the river bed.
During years <strong>of</strong> average to high run<strong>of</strong>f, particulate and dissolved nutrients (carbon, nitrogen, phos-
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