The Effects of Road Transport on Freshwater and Marine Ecosystems

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Water
Stormwater quality data from urban areas and from roads and motorways has shown that dissolved
concentrations <strong>of</strong> metals such as Cu and Zn can reach very high concentrations in the first flush <strong>of</strong>
stormwater. Over the duration <strong>of</strong> storm events, the concentration <strong>of</strong> dissolved zinc is the most significant
in relation to water quality guidelines such as ANZECC (2000). <strong>The</strong> regular exceedence <strong>of</strong> dissolved
concentrations suggests the likelihood <strong>of</strong> adverse effects on freshwater biota. Much <strong>of</strong> the copper in
stormwater may be complexed by dissolved organic matter. Only a limited proportion <strong>of</strong> the dissolved Zn
is likely to be complexed leaving most as the dissolved cation. A range <strong>of</strong> organic compounds, are
present in urban and road stormwater. However, there is little evidence <strong>of</strong> organic compounds in roading
stormwater being toxic and causing adverse effects on freshwater biological communities.
Available information indicates that the concentrations <strong>of</strong> metals in stormwater run<strong>of</strong>f are typically low
compared to water quality guidelines. However it is considered that longer-term exposure may have at
present unidentified chronic effects <strong>of</strong> freshwater organisms present in waterways receiving road and
highway run<strong>of</strong>f.
A range <strong>of</strong> toxicity studies, have been undertaken using urban stormwater discharging to freshwater
environments. Published toxicity test data has shown that first flush stormwater will exhibit greater
toxicity than flow weighed samples in some circumstances. Toxicity testing undertaken using Microtox
have shown that for run<strong>of</strong>f parking areas, 50% <strong>of</strong> samples are toxic and for highways (e.g., isolated
bridge run<strong>of</strong>f), 20% <strong>of</strong> samples were severely toxic. Studies involving freshwater algae have shown that
nutrients in run<strong>of</strong>f may stimulate growth but that metals in stormwater may inhibit growth. Work in New
Zealand has shown that urban stormwater has chronic effects on the growth <strong>of</strong> freshwater algae.
Tests carried out using a range <strong>of</strong> freshwater organisms and have not demonstrated consistent toxicity.
Work undertaken using general urban run<strong>of</strong>f has shown toxicity but the toxic agent was considered to be
in some studies to be organic compounds (and in some cases in the US to be pesticides used in
residential areas). Urban stormwater testing has shown that 40% <strong>of</strong> all stormwater samples
demonstrated toxicity to D magna and variable toxicity to species such as Ceratodaphnia and no toxicity
to others. Given the nature <strong>of</strong> stormwater run<strong>of</strong>f and samples collected from roads, there may be
limitations in the representativeness <strong>of</strong> some toxicity tests.
Freshwater organisms below stormwater outfalls are exposed to pulses <strong>of</strong> contaminants following rainfall
events. <strong>The</strong>y may be exposed to a first flush containing significant concentrations <strong>of</strong> some contaminants.
This may be followed by lower level prolonged exposure.
Sediments
Build-up <strong>of</strong> sediment discharged from roadways will occur close to the point <strong>of</strong> discharge (in ponds,
wetlands, streams and lakes) if the discharge point does not have sufficient energy to transport the
contaminants and sediment away. Based upon the composition <strong>of</strong> the suspended sediment and
measurement <strong>of</strong> urban stream sediment quality, it is likely that concentrations <strong>of</strong> contaminants can buildup
to concentrations that could have an adverse effect on freshwater benthic organisms.
Given the concentration <strong>of</strong> Cu, Pb and Zn in the suspended sediments <strong>of</strong> stormwater draining roads,
exceedence <strong>of</strong> sediment quality guidelines would be expected. Depending upon the ratio <strong>of</strong> stormwater
sediment to uncontaminated stream sediments, elements such as Zn may exceed guidelines at which
adverse effects (on benthic organisms) could be expected to occur. In urban areas however, streams
may not receive their normal supply <strong>of</strong> sediments and as a result sediments derived from roadways and
other urbanised sources may dominate the sediments in the stream.
For lakes, the concentration <strong>of</strong> contaminant in sediment will depend on the distribution and build-up <strong>of</strong>
contaminants in the lake bed following stormwater discharge to the lake. Contaminant build-up in small
lakes with low natural sediment budgets would be expected. Available data indicates that contaminant
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