Nav: Home

Greenhouse gases: First it was cows -- now it's larvae!

March 14, 2017

Chaoborus spp is a small fly species that is found all over the world (except in Antarctica). The insect spends one to two years of its life cycle under water in a larval state, in lakes no deeper than 70 metres. Larvae spend the day in lakebed sediment and rise to the surface at night time to feed. They are equipped with air sacs that they can adjust to alter their depth in the water so as to migrate upwards and downwards. Scientists at the University of Geneva (UNIGE), Switzerland -- in collaboration with Berlin's Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Potsdam University and Swansea University -- have discovered that Chaoborus spp also uses the methane it finds in lakebeds to help it move around. The species releases methane into the surface water, increasing the likelihood that the gas will enter the atmosphere. The research, which has just been published in Scientific Reports, demonstrates the negative role played by the larvae not just in global warming but also in disturbing the sedimentary layers at the bottom of lakes.

The life cycle of the small fly Chaoborus spp has been well-known for almost a century. Scientists at the time discovered that during the larval stage (the longest phase of its cycle), the larva is armed with small air sacs -- vesicles -- that it uses to navigate between the lake surface, where it feeds, and the sediment at the bottom of the lake, where it protects itself from predators and the heat of the day. Chaoborus spp can adjust its position in the water by inflating these air pockets to rise to the surface or, conversely, compress them to descend again. However, at a depth of 70 metres, it is impossible for the larva to inflate its vesicles due to the water pressure that is exerted on them. So, what does it do? This is the question that the team examined, led by Professor Daniel McGinnis, from the F.-A. Forel Department in the Science Faculty at the University of Geneva, in collaboration with IGB in Berlin, Swansea University and Potsdam University.

«Methane is a gas that is not very soluble in water. We know that it is present in very large quantities in anoxic sediments (depleted of oxygen), and that it exceeds the solubility capacity in water and forms small bubbles. Therefore, we hypothesised that the Chaoborus spp larvae absorb excess gas bubbles in order to inflate their vesicles, in spite of the water pressure, and are thus able to travel back to the surface,» explains Professor McGinnis. The scientists did indeed find that methane, since it prefers air to water, slides naturally into the larva's gas sacs, enabling it to re-inflate them and effortlessly reach the surface. Thanks to this ingenious inflatable «lift» system, Chaoborus spp saves up to 80% of the energy it would spend if it had to swim to the surface. Consequently, the larvae require less food and can expand their habitat.

Chaoborus spp larvae: exacerbating the greenhouse gas effect

The scientists subsequently wanted to know what larvae do with the methane they store. «First we put the larvae in an flask containing water that was rich in methane; then we moved them into methane-poor water," continues McGinnis. "After taking measurements, we observed that the methane level increased in proportion to the amount of larvae present. In other words, the larvae releases this gas into the water once they reach the surface.» Fresh water is responsible for 20% of natural methane emissions, and methane absorbs 28 times more heat than CO2; it has a significant impact, in short, on the greenhouse gas effect. Under normal conditions, methane is isolated and stored in lake sediments. However, the Chaoborus spp larvae let the gas out of this zone and increase its chances of reaching the atmosphere. They are, therefore, partly responsible for global warming.

What can be done about the situation? «The Chaoborus spp larvae, whose density ranges from 2,000 to 130,000 individuals per square metre, are only found when water is of poor quality, i.e. when it contains too many nutrients," adds Professor McGinnis. "So this means improving water quality and the way we monitor agriculture and treat waste water. The larvae also allow some pollutants to reach the surface since they bring particles of sediment up with them.

Chaoborus spp: an obstacle in studying lake sediment

Paleolimnology is the study of water through the ages. The discipline is based on analysing the various layers of sediment found in bodies of water, with the striae enabling scientists to investigate the different states of water over the centuries. Yet, this is only possible if sediment has been allowed to settle and solidify in lakebeds without being disturbed. But, once again, the Chaoborus spp larvae disrupt these analyses since they stir up the layers of sediment when hiding away during the daytime. Consequently, scientists no longer have access to reliable striae for analysis. Professor McGinnis concludes, "In summary, although it is fascinating to study the insect, the presence of Chaoborus spp is always a bad sign for the health of an ecosystem. At the same time, it gives us one more reason to safeguard good water quality in our lakes".
-end-


Université de Genève

Related Global Warming Articles:

Intensified global monsoon extreme rainfall signals global warming -- A study
A new study reveals significant associations between global warming and the observed intensification of extreme rainfall over the global monsoon region and its several subregions, including the southern part of South Africa, India, North America and the eastern part of the South America.
Global warming's impact on undernourishment
Global warming may increase undernutrition through the effects of heat exposure on people, according to a new study published this week in PLOS Medicine by Yuming Guo of Monash University, Australia, and colleagues.
Global warming will accelerate water cycle over global land monsoon regions
A new study provides a broader understanding on the redistribution of freshwater resources across the globe induced by future changes in the monsoon system.
Comparison of global climatologies confirms warming of the global ocean
A report describes the main features of the recently published World Ocean Experiment-Argo Global Hydrographic Climatology.
Six feet under, a new approach to global warming
A Washington State University researcher has found that one-fourth of the carbon held by soil is bound to minerals as far as six feet below the surface.
Can we limit global warming to 1.5 °C?
Efforts to combat climate change tend to focus on supply-side changes, such as shifting to renewable or cleaner energy.
Global warming: Worrying lessons from the past
56 million years ago, the Earth experienced an exceptional episode of global warming.
Global warming: More insects, eating more crops
Rising global temperatures are expected to significantly increase crop losses from insects, especially in temperate regions, a new study finds.
Global fisheries could still become more profitable despite global warming
Global commercial fish stocks could provide more food and profits in the future, despite warming seas, if adaptive management practices are implemented.
Global warming may be twice what climate models predict
Future global warming may eventually be twice as warm as projected by climate models under business-as-usual scenarios and even if the world meets the 2°C target sea levels may rise six metres or more, according to an international team of researchers from 17 countries.
More Global Warming News and Global Warming Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Accessing Better Health
Essential health care is a right, not a privilege ... or is it? This hour, TED speakers explore how we can give everyone access to a healthier way of life, despite who you are or where you live. Guests include physician Raj Panjabi, former NYC health commissioner Mary Bassett, researcher Michael Hendryx, and neuroscientist Rachel Wurzman.
Now Playing: Science for the People

#544 Prosperity Without Growth
The societies we live in are organised around growth, objects, and driving forward a constantly expanding economy as benchmarks of success and prosperity. But this growing consumption at all costs is at odds with our understanding of what our planet can support. How do we lower the environmental impact of economic activity? How do we redefine success and prosperity separate from GDP, which politicians and governments have focused on for decades? We speak with ecological economist Tim Jackson, Professor of Sustainable Development at the University of Surrey, Director of the Centre for the Understanding of Sustainable Propserity, and author of...
Now Playing: Radiolab

An Announcement from Radiolab