The Effects of Road Transport on Freshwater and Marine Ecosystems

59
<strong>The</strong> following parts <strong>of</strong> this section <strong>of</strong> the report aim to:
1. Identify the range <strong>of</strong> tools available to freshwater managers for assessing and monitoring in-stream
biota in New Zealand.
2. Briefly describe the general utility <strong>of</strong> available tools for assessing and monitoring freshwater biota.
3. Evaluate the applicability <strong>of</strong> each <strong>of</strong> the available tools to assessing road transport effects on
freshwater ecosystems.
4. Identify gaps in the current range <strong>of</strong> tools and evaluate additional tools for helping assess road
transport effects.
6.2.2 In-stream Habitat
In-stream habitat incorporates all aspects <strong>of</strong> physical and chemical constituents along with biotic
reactions (USEPA 1997). For the purposes <strong>of</strong> this investigation "habitat" has been defined to include
the following elements:
Stream-bed substrate.
Organic in-stream debris.
Stream channel banks.
Morphological subsections (riffles, runs and pools).
Riparian vegetation
<strong>Effects</strong> <strong>of</strong> road run<strong>of</strong>f on in-stream and riparian habitat
In-stream habitat plays an important role in determining the health <strong>of</strong> the biological communities
present. <strong>Road</strong> run<strong>of</strong>f has the potential to compromise in-stream habitat quality by affecting the habitat
elements listed above. <strong>The</strong> most significant mechanism for these changes is through the input <strong>of</strong>
sediment. As described in Section 2, total suspended sediment is a significant component <strong>of</strong> road
run<strong>of</strong>f pollution (Barrett et al. 1995). Sediment inputs can result in degraded in-stream habitat quality.
Examples <strong>of</strong> the types <strong>of</strong> changes in habitat quality that arise from sediment inputs into urban streams
include:
Poorly sorted mobile sediments in runs and riffles.
Reduced habitat diversity.
Reduced benthic primary production through smothering <strong>of</strong> algae.
Clogging <strong>of</strong> interstitial spaces.
Poorly differentiated pools, riffles and runs.
Schueler (1996) identified that stream channel geometry stability can be a good indicator <strong>of</strong> the
effectiveness <strong>of</strong> stormwater control practices. It was identified in that review that once catchment
areas have more than 10 to 15% imperviousness alterations to waterway channel morphology occur.
Brookes (1988) also identified stream morphological changes related to urbanisation. <strong>The</strong>se physical
changes are primarily responsible for habitat change and loss then has subsequent adverse effects on
aquatic communities.
Stormwater from roads will transport gravels and finer particulate material that may cause local changes
in substrate conditions near the discharge point. <strong>The</strong> significance <strong>of</strong> the change will depend upon the
local sediment type and environment. <strong>Transport</strong> <strong>of</strong> finer particulate material downstream may contribute
changes to particle types in sediment (e.g., particles <strong>of</strong> asphalt or bitumen – refer Faure et al. 2000) but
these changes are not likely to result in significant enough habitat changes which may then induce
changes in biological community composition.
Kingett Mitchell Ltd
Resource & Environmental Consultants