Midge fossils reveal methane release from lakes
Maarten van Hardenbroek explored a new method to reconstruct past methane availability in lakes, using the chemical composition of certain groups of non-biting midges and other invertebrates. Lakes can be important, but often ignored sources of the greenhouse gas methane. In order to understand increasing methane emissions in the present, methane variations during past periods of climate change are studied. On 10 January Maarten van Hardenbroek will defend his PhD thesis.
You are what you eat
Several invertebrates, including larvae of non-biting midges, feed on
methane-oxidizing bacteria that have distinctly low stable carbon isotope values (d13C). These low stable carbon isotope values are also found in the fossil remains of the invertebrates, based on the principle ‘you are what you eat’. Invertebrate remains preserve well in lake sediments and can be used examine the availability of methane in the past.
Sweden and Siberia
In lakes in Sweden and Siberia a relationship was found between methane release and stable carbon isotope values of invertebrate remains collected from modern surface sediments. Stable carbon isotope values in the remains of certain non-biting midges and water fleas appeared to be especially sensitive to the availability of methane. Subsequently, the sensitivity for methane of these groups was used to
reconstruct the importance of methane in the past 1400 years based on a sediment
core from a Siberian lake.
More methane in warmer periods
Maarten van Hardenbroek found lower stable carbon isotope values in invertebrate remains during warm periods (AD 860-1150 and since AD 1970) than during colder periods. This suggests that more methane became available in this lake during warmer periods.
Thesis title
Stable carbon isotopes of invertebrate remains: do they reveal past methane release from lakes?
Promotor: Prof. dr. Andy Lotter
Co-promotor: Dr. Oliver Heiri
Date: 10 January 2011
Time: 4.15 p.m.
Location: Academiegebouw, Domplein 29, Utrecht.
Darwin program 1044: Chironomid 13C as a proxy of past methane emission from thermokarst lake sediments: development, calibration and application