Some lakes stay turbid at nutrient levels where they should be clear — and clear where they should be turbid. The biomanipulation and alternative-stable-states framework explains why, and when reshaping the food web can flip a lake to a self-stabilising clear-water regime and hold it there.
Biomanipulation is not a universal fix — it works only within a window of nutrient concentration and where the food web can be shifted durably. Our ecological-state assessment tests whether a lake is in, or can be pushed into, the clear-water stable state, so the lever is used where it will actually hold.
Explore Our ProcessRemoving the right predator can ripple down the food web to the water clarity
Piscivores control planktivorous fish; planktivores control grazing zooplankton; zooplankton control phytoplankton. Reduce planktivore pressure — by promoting piscivores or removing coarse fish — and large Daphnia rebound and graze the algae down, clearing the water from the top of the food web.
Scheffer’s framework shows shallow lakes have two self-reinforcing states over a range of nutrient levels: a clear, macrophyte-dominated state and a turbid, algae-dominated one. Each resists change — macrophytes stabilise clarity; turbidity shades them out — so a lake tends to sit firmly in one.
Because each state defends itself, the nutrient level needed to flip a turbid lake clear is lower than the level that first tipped it turbid. This hysteresis is why simply easing nutrients may not recover a lake — and why a biomanipulation “shock” can be needed to cross back.
The alternative-stable-states model treats turbidity as a function of nutrients with positive feedbacks: submerged macrophytes suppress resuspension and algae (stabilising the clear state), while phytoplankton turbidity shades macrophytes out (stabilising the turbid state). Over an intermediate nutrient band both states are stable, separated by an unstable threshold — a critical turbidity. A lake will not move until it is pushed past that threshold, which is the mechanism behind hysteresis: the phosphorus concentration that returns a turbid lake to clarity is well below the one that originally caused the collapse. Biomanipulation works by forcing the system across the threshold — a sharp reduction in planktivorous fish releases zooplankton grazing, algae crash, light reaches the bed, macrophytes establish, and the feedbacks then hold the new clear state. The quantitative test before acting is whether the lake’s nutrient level sits inside the bistable window: too high and the clear state is not stable (manipulation relapses); low enough and a one-off intervention can lock in a lasting clear-water regime. That window, read against the phosphorus budget, is what tells us whether the food-web lever will pay off.
Diagnosis first, intervention only where it will hold
We establish which stable state the lake occupies and whether its nutrient level sits within the bistable window where a flip can be made durable.
Biomanipulation is paired with nutrient or internal-load control so the clear state is not undermined by a phosphorus level that keeps the turbid state stable.
We design the macrophyte-establishment and fish-management follow-through that holds the new state against relapse.
Reynolds & Bauhm diagnoses the ecological state, tests whether the nutrient level allows a durable flip, and designs the biomanipulation-plus-nutrient strategy that holds the clear-water regime.
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