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:

Containing methane and its contribution to global warming
Methane is a gas that deserves more attention in the climate debate as it contributes to almost half of human-made global warming in the short-term.
Global warming and extinction risk
How can fossils predict the consequences of climate change? A German research team from Friedrich-Alexander Universität Erlangen-Nürnberg (FAU), the Museum of Natural History Berlin and the Alfred Wegener Institute compared data from fossil and marine organisms living today to predict which groups of animals are most at risk from climate change.
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 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.
More Global Warming News and Global Warming Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Teaching For Better Humans 2.0
More than test scores or good grades–what do kids need for the future? This hour, TED speakers explore how to help children grow into better humans, both during and after this time of crisis. Guests include educators Richard Culatta and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#556 The Power of Friendship
It's 2020 and times are tough. Maybe some of us are learning about social distancing the hard way. Maybe we just are all a little anxious. No matter what, we could probably use a friend. But what is a friend, exactly? And why do we need them so much? This week host Bethany Brookshire speaks with Lydia Denworth, author of the new book "Friendship: The Evolution, Biology, and Extraordinary Power of Life's Fundamental Bond". This episode is hosted by Bethany Brookshire, science writer from Science News.
Now Playing: Radiolab

Dispatch 3: Shared Immunity
More than a million people have caught Covid-19, and tens of thousands have died. But thousands more have survived and recovered. A week or so ago (aka, what feels like ten years in corona time) producer Molly Webster learned that many of those survivors possess a kind of superpower: antibodies trained to fight the virus. Not only that, they might be able to pass this power on to the people who are sick with corona, and still in the fight. Today we have the story of an experimental treatment that's popping up all over the country: convalescent plasma transfusion, a century-old procedure that some say may become one of our best weapons against this devastating, new disease.   If you have recovered from Covid-19 and want to donate plasma, national and local donation registries are gearing up to collect blood.  To sign up with the American Red Cross, a national organization that works in local communities, head here.  To find out more about the The National COVID-19 Convalescent Plasma Project, which we spoke about in our episode, including information on clinical trials or plasma donation projects in your community, go here.  And if you are in the greater New York City area, and want to donate convalescent plasma, head over to the New York Blood Center to sign up. Or, register with specific NYC hospitals here.   If you are sick with Covid-19, and are interested in participating in a clinical trial, or are looking for a plasma donor match, check in with your local hospital, university, or blood center for more; you can also find more information on trials at The National COVID-19 Convalescent Plasma Project. And lastly, Tatiana Prowell's tweet that tipped us off is here. This episode was reported by Molly Webster and produced by Pat Walters. Special thanks to Drs. Evan Bloch and Tim Byun, as well as the Albert Einstein College of Medicine.  Support Radiolab today at Radiolab.org/donate.