Chironomids as environmental indicators

Chironomidae are a family of Diptera, the two-winged flies. Their abundance in freshwater systems and stenotopic characteristics make them ideal environmental indicators.

Characteristics

The life cycle of chironomids will only be completed if the environmental conditions are suitable as they are sensitive to: 

  • summer temperatures
  • the relative acidity (pH) of the water 
  • amount of nutrients in the lake water
  • the presence of pollution or trace metals

The heads of the larval stage are deposited and usually well-preserved in lake sediments after each moult as they grow. The heads build up year after year in the sediment providing a natural archive of the chironomid species that have lived in the lake.

Past climates

Records from weather stations do not extend back long enough to capture the full extent of natural climate variability needed to be able to predict future climate change.

By finding out which temperatures, pH or nutrient concentrations are favoured today by particular species of chironomids we are able to quantify past environmental conditions from the preserved head capsules.

After analysing a lake sediment core several metres long, sliced at intervals of 1cm or less, and dated using radiocarbon, a highly detailed record of past environmental and climatic change over thousands of years can be reconstructed.

  • Chironomid mouth parths
    The midge thermometer

    By studying the optimum summer temperature of over 200 common chironomid species a ‘midge thermometer’ has been developed accurate to within 1°C.

Glossary

Stenotopic
An animal or plant that is only able to adapt to a narrow range of environmental conditions.