Aquatic biodiversity

Roadside vegetation

Within the Wagga Wagga LGA there is an extensive road network that connects the rural landscape and includes a combination of principal, secondary and minor roads as well as tracks. The vegetation within the adjoining roadside reserves is diverse and ranges from native woodland to scattered paddock trees. Many of the vegetation communities within roadside reserves are listed as threatened ecological communities under both Commonwealth and State legislation and hold significant conservation value.

Roadside vegetation can vary considerably and occurs in patches of variable size and is often highly fragmented. This increases the importance of roadside vegetation as stepping stones between remnant patches. Remnants provide valuable wildlife habitat and support areas of core habitat when linked to other vegetation across the landscape. Council has recognised the significance of roadside reserve networks and the benefits these areas provide toward maintaining diverse and functional ecosystems to support native fauna and has developed a Roadside Vegetation Management Plan that will help guide management practices that will maintain or improve conservation significance within the roadside reserves. Council also recognises the need to minimise potential conflict and ensure roadside vegetation is managed to ensure a balance between biodiversity and the ability to maintain community infrastructure and public safety.

Bushfires

Bushfires are a natural part of Australia’s environment. Many of Australia’s native plants are fire prone and combustible, and numerous species depend on fire to regenerate. Natural ecosystems have evolved with fire, along with biological diversity, which has been shaped by both historic and contemporary fires. First Nations Peoples have been using fire as a land management tool for thousands of years (Geoscience Australia, 2019)

Whether a bushfire will occur depends on the presence of fuel, oxygen and an ignition point source. Fire intensity and speed depends on ambient temperature, fuel load, fuel moisture, wind speed and slope. (Geoscience Australia, 2019) One way to minimise the effects of bushfires is through hazard reduction or fuel reduction and cultural burning. This is a process that takes place before fire season where the fuel load is reduced by controlled burns, mechanical clearing (slashing undergrowth) or reducing ground fuel load by hand. (NSW Rural Fire Service, 2019)

Fire practice continues to be used to clear land for agricultural purposes and to protect properties from intense uncontrolled fires (Geoscience Australia, 2019). The loss of biodiversity in fires can also be severe. Almost three billion animals are estimated to have been killed or displaced from the 2019 ‘Black Summer’ bushfires, including 143 million mammals, 246 billion reptiles, 180 million birds and 51 million frogs (Van Eeden, et al., 2020).

Aquatic biodiversity

The Fisheries Management Act 1994 defines fin-fish, crustaceans, molluscs, worms, insects and other aquatic invertebrates as ‘fish’. Due to the degradation of inland river systems such as the loss of aquatic habitat, aquatic biodiversity is in decline. Aquatic habitats differ from terrestrial habitats and are more susceptible to damage and loss. The Murrumbidgee River is the most prominent water course in the Wagga Wagga LGA. It provides the city centre with numerous recreational opportunities and is an important source of irrigation for various types of agricultural activities in the Riverina district. The Murrumbidgee River also has a great deal of cultural significance for the Wiradjuri community, the traditional owners of this land.

In Wiradjuri, Marrambidya Bila means big water, big boss

As well as the Murrumbidgee River, the Wagga Wagga LGA has a number of other water bodies, including:

Lake Albert Wollundry Lagoon Flowerdale Lagoon Bomen Lagoon Marrambidya Wetlands Many streams, creeks and wetlands

These water bodies (even those that do not permanently hold water) represent important habitat for both aquatic and terrestrial animals and are considered ‘Key Fish Habitat’. Figure 3 illustrates the key fish habitats identified in the Wagga Wagga LGA.

At different times, these water bodies have suffered from water shortages, damaging floods, bank erosion, salinity, litter and pollution, cold water releases that upset breeding cycles, algae and invasion by carp and weeds.

Flooding

Given the proximity of the Murrumbidgee River, parts of the Wagga Wagga LGA are prone to flooding. A large part of the city centre remains on the floodplain and is protected from flooding by levee banks. Due to river regulation and flood mitigation works, the area of floodplains inundated by natural flood flows has been reduced. This reduces the area available for nutrient cycling and affects many ecological processes. As a result, floodplain productivity, fish productivity and flood dependent populations are reduced.

Areas have experienced riverine flooding on numerous occasions, requiring large scale evacuations and resulting in considerable damage. The Floodplain Management Plan identified a number of factors such as development, storage dams, levees and vegetation as well as other factors that have contributed to the increased roughness (measure of the amount of frictional resistance water experiences when passing over land and channel features) of the flood plain, which has contributed to potential flood height increases.

The Vegetation Management Plan, developed in response to this, identified a number of vegetation management activities that could be implemented to reduce “roughness” on the flood plain. However, the modelled flood level reduction predicted from the vegetation management actions was less than expected and impacted negatively on erosion and ecological processes. The Vegetation Management Plan identified a number of opportunities to manage new growth as well as exotic plants such as willows and weeds. These actions will not provide wide scale flood level reduction but will manage new growth and weed densities so as not to increase flood levels into the future.

Stormwater run-off

Stormwater is rainwater that runs off impervious surfaces such as roofs, roads and pavements and green spaces, which is transported by the stormwater system. Unlike the sewerage system, the stormwater is untreated and discharges into natural waterways. Stormwater can carry various pollutants including litter, soil, organic matter, grease, oil and metals collected from roads and properties, and fertilisers and pesticides from gardens and parks. The pollutants entering the stormwater system and the waterways can cause severe environmental issues from damage to infrastructure (i.e. roads, culverts and stormwater pipes), algae blooms, entanglement of fauna, and contamination of water.

Salinity

Salinity is the build-up of salt in the upper layer of soil that had been brought to the surface by rising groundwater. This may be caused by removal of vegetation, overwatering of gardens and lawns, leaking underground water pipes and changes in land use. Salinity may cause the life span of infrastructure such as roads and footpaths to be reduced, damage to houses foundations, reduced water quality in creeks and rivers, and loss of vegetation where the soils are too saline for plants to grow.

Image: Chloe Smith