The Effects of Road Transport on Freshwater and Marine Ecosystems

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3. Increasing sediment inputs.
4. Increasing nutrient inputs.
5. Increasing contaminant loads.
<strong>The</strong> results <strong>of</strong> investigations into the effects <strong>of</strong> highway run<strong>of</strong>f on algae have to date been somewhat
contradictory. Dussart (1984) for example, reported that algal diversity and abundance increased
downstream <strong>of</strong> urban/highway run<strong>of</strong>f due to an increase in nutrient loadings and a decrease in
invertebrate algal grazers. Portele et al. (1982) on the other hand reported that algae biomass
decreased with increasing concentrations <strong>of</strong> highway run<strong>of</strong>f. Winters & Gindley (1980) concluded that
highway run<strong>of</strong>f has the potential to have an inhibitory or stimulatory effect on algae depending on the
chemical composition <strong>of</strong> the run<strong>of</strong>f (i.e., the presence <strong>of</strong> nutrients). Macaskill et al. (2003) identified
that stormwater run<strong>of</strong>f (From Rotorua City in New Zealand) has chronic effects on the growth <strong>of</strong> the
freshwater algae (Selenastrum capricornutum 72 hour growth inhibition toxicity test).
General Tools
USEPA (1998) describe a range <strong>of</strong> periphyton (algae, fungi, bacteria, etc.,) metrics currently in use in
the United States. Metrics listed include 7 diatom metrics and 6 non-diatom metrics including taxa
richness, indicator species, relative abundance, chlorophyll-a and ash free dry weight (AFDW).
Methods that use algal indicator organisms are complicated by spatial and temporal variability,
naturally rare species and problems associated with identification. However some species, which are
known to reflect certain water quality conditions, do provide useful information. In New Zealand
biomonitoring programmes have traditionally tended to focus on chlorophyll a, AFDW, and algal
abundance. Substantial work has been carried out on periphyton communities in New Zealand
waterways as a result <strong>of</strong> their effect on stream aesthetics and effect on quality <strong>of</strong> habitat for
invertebrates. <strong>The</strong> reader is referred to MfE (1992) and Biggs (2000) for further information.
Specific Tools for assessing road run<strong>of</strong>f effects
<strong>The</strong>re are no tools specifically designed to assess the effects <strong>of</strong> road run<strong>of</strong>f on algal communities.
Stream algal community composition and biomass reflect the nutrient status <strong>of</strong> the water. Urban
streams tend to have relatively high nitrogen and phosphorus inputs and reflect a variety <strong>of</strong> nutrient
sources within the urban environment. Isolating and quantifying the effect that nutrients within road
run<strong>of</strong>f have on algal communities from general urban run<strong>of</strong>f is therefore likely to be very difficult.
Overall, methods for the measurement and assessment <strong>of</strong> periphyton communities in waterways are
well developed in New Zealand. Use <strong>of</strong> these tools in localities where urban run<strong>of</strong>f contains significant
contribution from motor vehicles and general urban activities does not allow the specific effects
associated with road transport to be identified. However, in locations where stormwater discharges
from roads or highways is the sole contributor, the assessment <strong>of</strong> periphyton quality and composition
will provide information on effects <strong>of</strong> stormwater as it relates to that component <strong>of</strong> the freshwater
biological community.
International work suggests that urban stormwater and road run<strong>of</strong>f may have both inhibitory and
stimulatory effects on in-stream algal communities. <strong>The</strong> stimulatory effects arise from the nutrients
present in road run<strong>of</strong>f. <strong>The</strong> inhibitory effects arise from the presence <strong>of</strong> a variety <strong>of</strong> contaminants in
the run<strong>of</strong>f. In New Zealand general urban stormwater run<strong>of</strong>f has been shown to inhibit the growth <strong>of</strong>
freshwater algae.
6.2.4 Aquatic Invertebrates
Invertebrates (aquatic insects, molluscs, oligochaetes etc.,) that are ubiquitous in most stream
environments are sensitive to water and habitat quality. <strong>The</strong>se features make invertebrates important
tools for assessing and monitoring in-stream health. A range <strong>of</strong> invertebrate monitoring and
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