6. Noosa River DMP Ver0 (Combined)

5.3 Turbidity
Turbid plumes generated during the extraction activities will reduce light levels on the seafloor,
which could affect photosynthetic benthic species requiring light for energy production (e.g.
seagrass, algae, and soft coral). The impact of turbid plumes on these benthic primary
producers will depend on whether critical light requirements are met, and the magnitude,
frequency and duration of low light events (Flanagan Consulting, 2017).

Of the marine megafauna likely to be encountered within the Noosa River estuary (dugong,
dolphins and turtles), all are capable of foraging in turbid water. Dolphins often stir up bed
sediments when foraging for benthic prey, resulting in limited visibility for prey detection and
reliance on echolocation to detect prey (Morrell, 2011). Dugongs have poorly developed
eyesight and rely on bristles on their upper lip, rather than visual cues, to detect seagrass food
resources (Department of Environment (DE), 2020b). Flatback Turtles are known to feed in
turbid shallow waters (DE, 2020) and may not be directly affected by turbid plumes generated
by dredging. Other marine turtle species such as Green and Hawksbill Turtle, which feed on
seagrass and/or in reef environments, may avoid areas affected by turbid plumes.

5.4       Benthic Habitat
Soft unvegetated sediment habitat occurs within both the extraction and replenishment areas
and consists of sand to fine silt. Observations and video-based surveys undertaken
simultaneously with the seagrass assessment recorded evidence of bioturbation to a depth of
approximately 2.5 m.

Initially, extraction will cause a temporary loss of biota, since benthic communities typically
inhabit the surface sediments that will be removed. Likewise, benthic communities will be
disturbed by the addition of substrate. Modifications to benthic habitats are expected to initially
result in highly localised reductions in benthic fauna richness and abundance. However, the
sides of a natural channel are dynamic and benthic communities are known to recover rapidly
at dynamic sites (DPI&F, 2007). Dynamic sites are also likely to fluctuate in response to natural
disturbances, such as extreme weather events. Localised reductions of benthic fauna are not
expected to cause detectable flow-on effects to other ecosystem components or functions
beyond the extraction and replenishment footprints.
It is recommended that best practice procedures are followed, as detailed in the Fish Habitat
Management Operational Policy FHMOP 010 (2007). Tidal fish habitats, erosion control and
beach replenishment. This includes, but is not limited to:

      •    Extraction should not be undertaken more frequently than every two years from the same
           site to allow time for benthic community recovery between events;
      •    Extraction and replenishment should be undertaken outside of migration and breeding
           times of important fisheries and forage fish species (closed season for fin fish species
           occurring in the Noosa River is from July to August);
      •    Extraction of material should be prior to major benthic invertebrate recruitment times
           (e.g. for south-east Queensland, spring is the major recruitment time), to enhance
           recovery times at the extraction site; and
      •    Material should be deposited on the receiving site in a spray of sand and water or in a
           number of shallow layers (e.g. up to 20cm depth per layer) to maximise survival and
           vertical migration by resident infauna.


Noosa River                                                                                Page 13
Marine Plant Impact Assessment
Project Number: BC-20067