Thresholds

lakes, agriculture and thresholds

It is difficult to identify the precise location of a threshold. This example uses phosphorus in lakes from agriculture to exemplify identifying factors that will push the system beyond a threshold. The concentration of phosphorus in lake sediments is a key factor determining whether the lake tends to be clear with green plants (one state), or murky with algae blooms (alternate state).

Goulburn-Broken Catchment

A climatic event such as multiple, consecutive wet years in Southern Australia for example, may have caused no significant change in decades past, but today with reduced tree cover and over-irrigation causing water tables to rise near the surface, the threat of extensive and irreversible salinization of prime agricultural land looms.  The gradual loss of resilience in this case is linked to multiple variables including the obvious - in retrospect, clearing of native vegetation following colonization, but also the social values driving agricultural expansion, overseas markets, and development of water infrastructure.

Coral reefs

Loss of herbivores and the addition of nutrients are the main causes of coral reef degradation. These, plus the presence of global stressors like global warming and ocean acidification require a governance intervention to prevent the transgression of a threshold or to navigate the reverse trajectory away from a stable degraded state.

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