Alternative Stable States in Shallow Lakes: What Causes a Shift?
Lake T�E5;kern and Lake Krankesjön, two shallow, moderately eutrophic, calcium-rich lakes in southern Sweden have shifted between turbid and clearwater states several times during the past decades (Fig. 26.1). Lake Krankesjön shifted from a clearwater state with abundant submerged vegetation to a turbid state with sparse vegetation during the mid-1970s (Karlsson et al., 1976) and back to a clearwater state during 1985. Today, the lake is in the clearwater state, with abundant submerged vegetation dominated by Charophyta (Blindow et al., 1993; Fig. 26.2). Both shifts coincided with deviations from the average water level. During the mid-1970s, the water level during spring and summer was about 15 cm higher than average, whereas it was about 10 cm lower than average during 1983-1985 (Blindow, 1992).
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