Balaton: A case of Regime Shift
Critical transitions: the Balaton case and a point made for resilience management.
Suddenly and somewhat surprisingly, the famous lake Balaton tourist destination became increasingly greenish and opaque by the end of the 1970s. As a consequence of deteriorating water quality, the change occurred rapidly, resulting in enormous ecological consequences: the death of many animals and plants. The main livelihood of the local people, tourism, also suffered a serious blow. What has happened? The management of the lake did not change much in the past decade. What happened, then?
One of the most important concepts in resilience theory is regime shifts, or in other words, critical transitions. These are large scale changes in social-ecological systems that happen relatively fast and are very hard to reverse. These changes occur suddenly often after a longer period of invisible preparation.
The eutrophication of Balaton was also a regime shift that was in preparation for decades. It started in the ’50s with the massive intensification of agriculture within the watershed, resulting in significant phosphorus pollution — first in the soil, then in the water. The lake sediment had a significant capacity to accumulate and to bind the pollutant, so it could not cause much damage for at least two decades, but after that period of time, this capacity was overwhelmed by the continuing pollution, and phosphorous concentration started to increase in the waterbody as well. As phosphorus is used as a fertilizer on land, it has a similar effect on the water, too: algae started to be produced en masse, making the water murky and greenish. This change had many other consequences: as the water turned murky, no light could reach the submerged plants in the water — this killed these plants in a short time. Losing them also removed their roots, which stabilized the sediment — this change leading to even more phosphorus to be released, making the problem worse. The changes in vegetation also reduced the oxygen concentration in the water, another factor that facilitated the release of phosphorus from the chemical bonds it stored for a long time.
As the shift happened, all the past pollutants that were safely stored in the sediment became available, reinforcing and stabilizing this new state of the lake. The sediment that was once a sink for the pollutant now became a source of it.
These are the self-reinforcing processes that are stabilizing a new stable state. Before the regime shift happened, a relatively moderate effort could have prevented it; after the transition, reversing the transformation needs a heroic intervention — if possible at all.
