Chironomids as environmental indicators

Museum scientists have developed a 'midge thermometer' that allows us to reconstruct a highly detailed record of environmental and climatic change over thousands of years, accurate to within 1°C.

The abundance of Chironomidae in freshwater systems and their sensitivity to environmental conditions make them ideal environmental indicators.

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

Methods

Chironomids will only complete their life cycle if the environmental conditions are suitable. 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.

By studying the optimum summer temperature of over 200 common chironomid species we have established a 'midge thermometer'. Comparing the modern air temperature of a lake with the temperature estimated from the chironomid assemblage we find that our midge thermometer is accurate to within about 1°C of the actual temperature.

We can now estimate past air temperatures by identifying the most abundant chironomid species in lake sediment cores and their optimum temperature, reconstructing highly detailed records of past environmental change.