Shallow lakes in the Netherlands Pristine state: Clear water Abundant - PowerPoint PPT Presentation

Shallow lakes in the Netherlands Pristine state: Clear water Abundant submerged vegetation G Gradual increase in nutrient d l i i i loading from agricultural run ‐ off Sudden transition to turbid state characterized by S dd t iti t t bid t t h t i d b phytoplankton blooms, suspended sediment, little submerged vegetation submerged vegetation Decreases in nutrient loading unable to reverse g transition http://www.sparcs ‐ center.org/applications/ecology/lakes.html

A possible explanation: Alternative stable states Alternative stable states Submerged vegetation promoted water clarity by: water clarity by: • reducing nutrients in water column • providing habitat refuges for grazing zooplankton • preventing sediment resuspension http://www.sparcs ‐ center.org/applications/ecology/lakes.html

A possible explanation: Alternative stable states Alternative stable states Turbid state: • Lack of penetrating sunlight Lack of penetrating sunlight prevents re ‐ establishment of submerged vegetation g g • Eutrophication, reduction in zooplankton densities lead to phytoplankton blooms h l k bl • Benthic feeders (fish) stir up sediment sediment http://www.sparcs ‐ center.org/applications/ecology/lakes.html

from Scheffer & Carpenter, TREE 2003

from Scheffer et al, Nature 2001

Alternative stable states • Slow, gradual changes in environment cause sudden, unexpected changes in ecosystems (“tipping points”) • Changes are not easily reversed (hysteresis) (hysteresis) http://www.sparcs ‐ center.org/applications/ecology/lakes.html

Alternative stable states • Lakes in the Netherlands: Water clarity restored by reducing nutrient inputs and removing fish that were feeding in the benthos and on zooplankton and on zooplankton. • Other purported examples: Other purported examples: • Woodlands vs grasslands in terrestrial ecosystems • Desertification • Coral vs algal dominanted states in coral reefs t t i l f http://www.sparcs ‐ center.org/applications/ecology/lakes.html

Coral (C) Macroalgae (M) Turf (T) Photo credits P. Edmunds

sea urchins, Diadema antillarum (massive die ‐ off in 1983) parrotfishes p grazing grazing Macroalgae (M) Turf (T) Photo credits M. Chiappone, Wikipedia