Changing land use and management

2016

Land use and land management can produce pressures on aquatic environments that include changes to flow, water quality and the availability of habitat. As noted in SoE 2011, point sources of pollutants no longer significantly affect the aquatic environment. Diffuse sources, such as large-scale land clearing or changes to land cover, have left a legacy of changes in quality and flow regimes, such as changes in biota and sediment, and nutrient concentrations in streams. As an example, an extensive study of macroinvertebrate assemblages in Tasmanian streams confirmed the significant and widespread effects of livestock grazing on community structure (Magierowski et al. 2012). Elsewhere, a review of how forest cover affects flow found that, in catchments undergoing a permanent change in forest cover, it takes between 8 and 25 years for a catchment to reach a new equilibrium. Flow changes arising from the effects of different forest water use patterns included uniform changes in all flows, changes in numbers of zero flow days, and proportionally larger changes in low, compared with high, flows (Brown et al. 2013).

Since 2011, there have been no land-use changes or changes to management practices on a nationally significant scale. Land clearing continues across all Australian states, although at a much lower rate and with far more controls in place than in previous decades. Queensland’s land-clearing rate, which has risen from below 100,000 to nearly 300,000 hectares per year since 2010 (DSITI 2015), exceeds that of all other states and territories combined. Queensland’s clearing in recent years is dispersed across the state; no reports have been found of significant widespread hydrological impacts. See Box WAT3 for an example of best management practices in Queensland.

The broadest land-cover effects on water quality since 2010–11 are likely to have been those occurring across the Australian savannas and rangelands during the La Niña years following the millennium drought (see the Land report for details). This produced a spike in central Australian fires in late 2011 (Bastin 2011), including more than 5 million hectares burned in Tanami, Northern Territory. It is estimated that some 50–70 million hectares of the northern savannas burn each year, contributing to the ongoing tropical pressures on tropical aquatic ecosystems arising from fire regime changes from cool early-season burns to hot late-season burns.

In temperate zones since 2011, there were no bushfires on the scale of the 2009 Victorian Black Saturday fires. The largest fires, or series of fires, burned around:

  • 300,000 hectares in South Australia in 2014
  • 166,000 hectares in Victoria in 2014
  • 100,000 hectares in New South Wales in 2013
  • 100,000 hectares in Tasmania in early 2016.

The Black Saturday fires, which burned about 28 per cent of Melbourne’s forested water supply catchments, are predicted to reduce post-fire streamflow after 100 years by 1.4 per cent (around 12 GL per year) to 2.8 per cent (around 24 GL per year) under average climatic conditions. This low number is largely because of the low mortality of trees that were burned (Feikema et al. 2013). Other post-fire effects on inland water environments include increased sediment loads, and changes in nutrient, carbon and oxygen dynamics.

Other land use–related pressures on inland aquatic ecosystems include cover changes in areas of farmed land in Australia. This, and the area given to cropping, fluctuate by a few million hectares per year (Table WAT5; ABS 2014b, ABS 2016).

This follows a general decline during recent decades in the total Australian farm area, which, when combined with the adoption of best-practice farm management, lessens pressure from land use.

Table WAT5 Area of farmed and cropped land (’000,000 ha), 2011–13

Type of area

2011

2012

2013

2014

2015

Farmed

409.7

405.5

396.6

406.2

384.6

Cropped

32.1

32.0

31.6

25.6

26.1

 

soe-ig-inlandwater-1feb.png

Infographic

Argent RM (2016). Inland water: Changing land use and management. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/inland-water/topic/2016/changing-land-use-and-management, DOI 10.4226/94/58b656cfc28d1