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.