Thresholds Database > Lake acidification and population change, Ontario Canada

Background

Zooplankton and water chemistry were analysed from 47 lakes at least monthly for 1 year during the ice-free season. Zooplankton communities were compared among the lakes using crustacean species richness and a measure of species abundance. The relationship between zooplankton and acidity was modelled and a threshold of community change was identified at pH 6. This point represents a pH at which community composition changes most rapidly along the acidity gradient. The dominant source of acidity in the lakes is likely to come from atmospheric deposition.

Alternate Regimes

1. pH < 6;

High abundance of Leptodiaptomus minutus and Bosmima longirostris.

Fewer anomopods.

2. pH > 6;

Daphnia dubia and Sida crystallina only found at this level.

High abundance of D. mendotae, Cyclops bicuspidatus thomasi and Eubosmina longispina

Mechanism

Some species of zooplankton can no longer survive beyond a threshold level of acidity. The level of sensitivity varies among species. The threshold level of pH 6 identifies a point at which community composition changes most along the acidity gradient.

Management Decisions in Each Regime