The distribution of benthic invertebrates along a natural turbidity gradient in Lake Temiskaming,Ontario-Quebec

Lake Temiskaming, a rift valley lake on the Ontario-Quebec border, exhibits a permanent gradient of turbidity due to tributary streams which cut through clay deposits to the north of the lake. Concentrations of total phosphorus (TP) also decreased from north to south, with values suggesting mesotrophic conditions. Concentrations of chlorophyll a were characteristic of oligotrophic lakes and showed little relationship to either turbidity or TP. Large numbers of Tubificidae were found at our northernmost sampling station at a depth of 50 m, probably reflecting the localized impact of allochthonous organic matter introduced by a tributary stream. Numerical abundance of the benthic fauna was much lower and did not vary significantly among the six more southerly 50 m stations, but biomass declined from north to south as Heterotrissocladius oliveri relaced Pontoporeia hoyi. Numerical abundance did not differ significantly among stations at depths of 10 m, but biomass decreased from north to south reflecting the distributions of the largest species, Hexagenia sp. and P. hoyi. Intensive sampling on two transects showed that maximum numbers of invertebrates occurred in the profundal zone. While these results are consistent with the correlation between TP and zoobenthic biomass reported by other investigators, size selective predation by fish may also be important in controlling the distribution of benthic invertebrates in Lake Temiskaming.