Assessing or commenting on the resilience of inland water environments is challenging, because it can be difficult to recognise resilience when it occurs. In Australia’s environment, ecosystems have developed to be both resistant and resilient.

As evidenced in this and other 2016 SoE thematic reports, monitoring, assessing and reporting nationally and comprehensively on ecosystem states and trends are challenging enough once every 5 years, without the added challenge of considering whether a particular change observed in state, such as frog abundance, bears the characteristics of a resilient ecosystem. However, we need to consider whether our management is contributing to both a reduction in extreme and detrimental ecosystem disturbances, and an increase in the ecosystem characteristics needed to increase resilience. Management of streamflow releases, provision of environmental flows, and management to reduce impacts on groundwater levels and quality can all contribute to resilience. These contributions can then be considered when monitoring after an ecosystem shock—when detrimental changes that we have seen previously or that we expected to occur—were found either to have not occurred or to have been less severe.

Resilience is also often associated with active adaptive management (Allan & Stankey 2009). Adaptive management has been applied in various guises in Australian environmental management, although with few outcomes that assist in assessment of resilience.

SoE 2011 suggested that ‘the widespread floods of 2010 in drought-affected areas offer a tremendous opportunity to observe the response of extremely drought-stressed inland water systems, as do the releases of environmental flows in the Murray–Darling Basin and the Snowy River’, particularly as resilience-related ecosystem elements were viewed as compromised (e.g. Nicol 2009, Noell et al. 2009, Zampatti et al. 2010).

As noted earlier, the first outcomes of the Commonwealth Environmental Water Office’s Long-Term Intervention Monitoring Project have been reported. Among these, improved ecological resilience was achieved, envisaged or inferred through:

• improved condition of native vegetation communities in wetlands, including at the expense of exotic species, increasing resilience to future dry weather conditions (SECRC 2015)
• recruitment of waterbirds and fish as part of the larger-scale function of resilient biotic communities (Commonwealth Environmental Water Office 2015)
• multiple years of enhanced spring–summer flow, increasing the resilience of golden perch and silver perch populations in the lower Murray River (Ye et al. 2016)
• maintenance of aquatic habitat and support for ecological recovery (Watts et al. 2015)
• increased aquatic habitat on the western floodplain (Warrego River), increased productivity and basal food sources, and increased numbers and diversities of higher-level consumers such as frogs and birds (Commonwealth Environmental Water Office 2014)
• improved survival and condition of individuals through provision of individual refuges and improved ecosystem resistance (Commonwealth Environmental Water Office 2014)
• encouragement of natural thinning of river red gum seedlings, preventing river red gum encroachment and promoting re-establishment of aquatic vegetation communities (Commonwealth Environmental Water Office 2016).

In addition to resilience support through environmental flows, the potential for anthropogenic water bodies—such as agricultural ponds, irrigation channels, rural and urban drainage ditches, and transport canals—to offer refuges and increase resilience has been investigated. Chester and Robson (2013) found that freshwater anthropogenic habitats supported biodiversity and that this support could be enhanced through management actions, such as structural modifications and aquatic vegetation control.

In hydrological systems, resilience has been explored in recent years in relation to multiple stable ecosystem states. Various authors identified multiple steady states by conducting simulations from different initial state variables, some using advanced analysis techniques to quantify how the number of steady states may change with a single model parameter. A 2012 study (Peterson et al. 2012) found that switching between steady system states from wet or dry periods, such as with extended rainfall periods after drought, did not occur by crossing the threshold between the steady states. Rather, it occurred by exceeding the 2 steady-state domains, producing hysteresis. Therefore, consideration of stable ecosystem states in the context of resilience must consider the nature of change processes between those states.

A future opportunity for assessment of resilience in inland water environments lies in the assessment of the cumulative impacts of either negative factors, such as development and resource exploitation, or positive factors, such as beneficial co-management of water resources. The relevance of resilience here is that, often, ecosystems can resist or be resilient in the face of one or a few impacts, but this breaks down as impacts of different types and magnitudes accumulate, or as thresholds are reached (Standish et al. 2014). Similarly, recovery actions, such as environmental watering, pest reduction and competition management, may not have significant beneficial outcomes until a cumulative value or threshold is reached.