5. Commercial and non-commercial use

The impacts from port activities range from direct removal of habitat, for example, by capital and maintenance dredging of the seafloor, through to indirect environmental impacts, such as intermittent noise pollution (Section 5.8.3), dust, spills (cargo and pollutants) and light pollution from port infrastructure. The range of pressures on the environment are well documented.^1430,1431 Weighing up the degree of impacts from each type of port-related activity requires a site-specific assessment taking into consideration characteristics such as the local environmental conditions, volume of material dredged or dumped at sea, the type of dredging undertaken (capital or maintenance) and the configuration of port infrastructure.¹⁴³² 

Since 2019, port-related research has focused on expanding our understanding of how local environmental conditions, including resuspension of sediments, prevailing winds, tides and currents affect sediment loads and availability of benthic light. Understanding the spatial and temporal scale of the impacts from dredging activities (dredging and disposal of dredge material), and how these factors interact, is key to managing some of the impacts of maritime port development. In the Region, the major port dredging campaigns are generally restricted to the major trading ports. The local sediment and benthic characteristics of the 12 ports in the Region vary.

The impact of increased sediment due to dredging and disposal, and the extent to which sediment is resuspended by wind and waves, continues to be a focus of research and monitoring. New evidence continues to strengthen the hypothesis that port activities have adverse impacts on the marine environment at a local scale, but broader effects are more limited. In one 2019 study conducted outside the Region, the silt and clay content of the seabed was found to be 5-times higher after dredging, and it remained up to 2.5-times higher than the pre-dredging levels for up to 3 years after the dredging activities were completed.¹⁴³³ The in situ observations were used to analyse sedimentation and deposition rates at various distances from the dredging site. The majority (90 per cent) of the turbidity and light effects dissipated at around 20 kilometres from dredging site. The biological effects, including smothering of corals, were generally restricted closer to the dredging site (approximately 3 kilometres).¹⁴³³ However, more sensitive species may still be affected at further distances. A 2020 finding suggests that even in the presence of dredging activity, wind and waves can be the dominant drivers of turbidity and are often localised.¹⁴³⁴

Reef organisms are affected differently by changes in environmental conditions. The frequency and intensity at which they are exposed to these changes will also affect an organisms’ response. Acute and chronic exposure to reduced water quality caused by suspended dredging material will yield different physiological responses in benthic organisms that rely on photosynthesis for growth and survival.¹⁴³⁴ For example, the hard coral Pocillopora damicornis is sensitive to reduced light and may be a useful indicator of low light stress in coral communities during dredging.^679,1435 Port development rather than flooding may explain demographic variation in Australian humpback dolphins.⁵¹⁵

Management measures, such as environmental windows (periods of go-slow or, in some cases, no dredging), can minimise impacts to the values of the Region during periods of coral spawning, seagrass recruitment ¹⁴³⁶ and turtle breeding, and immediately following severe weather events.^{1408,1437,1438}

Other impacts, such as marine debris, artificial light and impacts on the Region’s aesthetic values can also result from port operations. Although the impacts of artificial light on some marine organisms are generally understood, light impacts from ports remains a knowledge gap. A report published in 2020 suggests that direct measurements of benthic light availability during dredging activities provide more ecologically relevant measurements than assessment of the water clarity.¹⁴³⁴ Measurements of particle size distribution and volume concentration profiles have become more common during dredge campaigns.^1439,1440 Budget and time constraints continue to be barriers to comprehensive data collection and analysis.¹⁴⁴¹

Since 2019, the port-led long-term monitoring programs have become more systematic and the data are publicly available, mainly due to the requirements of the statutory approvals process and actions driven by the Reef 2050 Plan. For example, in situ monitoring of light availability to benthic photosynthetic organisms ¹⁴⁴² and in situ dredge-induced sediment suspension information are collected in some port areas.¹⁴⁴³ Access to near real-time data to aid managing agencies in responsiveness is currently not available for dredging activities.³⁹ Long-term monitoring of seagrass at Port Curtis found that both area and biomass of the seagrass meadows had decreased since the previous survey in 2019 but remained greater than the long-term average.¹⁴⁴⁴ Monitoring at the port area in Cairns has showed a continued increase in seagrass biomass and a stabilisation of meadow area since 2019 against a historical low in the period from 2009 to 2011.¹⁴⁴⁵

Innovation and technological advances in modelling and in situ data capture during a capital dredge campaign in Cairns supported systematic, rapid and reproducible approaches to land disposal of the capital dredge material.¹⁴⁴⁶ A novel, beneficial reuse solution combining ecological and engineering goals to create ‘living seawalls’ may minimise connectivity impacts of intertidal port development.^1447,1448 The first empirical estimates during dredging of sediment accumulation were collected by deposition sensors in the port area in Townsville,¹⁴³⁴ and other studies are developing innovative methods and instruments to collect data.¹⁴³⁵

Ports are an established use of the Region and, as with any other use, their presence and ongoing operation continue to pose a range of threats to habitats and species at a local scale. Some impacts associated with the operation of the 12 ports in the Region have been reduced since 2019, while others persist. Of the impacts that remain, some could not be mitigated even with significant additional intervention, for example, the effects on aesthetic values or permanent removal of intertidal and inshore marine habitats.