Tag: paleoecology

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Three facts about chironomids and my first experiences with them

By Lilia Orozco

  1. Chironomids are not mosquitoes

When I started my doctoral research, I did not really know what chironomids were. I think I might have seen them in nature (my very first experience!) and confused them with something else. Chironomids are part of the same insect order as mosquitoes and flies, Diptera (1). Chironomids look like mosquitoes, but do not be mistaken: they lack the tube-like sucking mouth and do not bite, hence the name of non-biting midges. Chironomids are ubiquitous as long as there is enough moisture. Adults live only from a few days to a few weeks. As larvae, they live on the bottom of water bodies from rivers and lakes to puddles and sewage systems where they serve as food source for other animals, forming an important part of the food web.

Chironomid or non-biting midge by MarioQA licensed under CC BY-NC 2.0
  1. Paleoecologists study remains of chironomid larvae

Forget the study of fossil fake mosquitoes: paleoecologists are not in the search of wings and legs. Instead, chironomid larval stage has a hard head capsule that preserves well in lake sediments. Paleoecologists find them in ample amounts in sediment cores in comparison to other insect remains, which has generated many applications for chironomid head capsules in reconstruction of past environments since the late 1920s (2). The concept is simple, as larvae they live in the water, and consequently the aquatic environment has a strong influence on the species present and their abundance (1). Chironomids are sensitive to physical and chemical properties of the water; some species are indicators of water quality, while others are only found at certain depths or oxygen levels. However, it is summer climate what mostly determines the species distribution (3).

Photo of chirnomid larvae by Frank Fox, licensed under CC BY-SA 3.0

The particular ecologies and niches of the different chironomid species make them robust environmental indicators. In the early applications, chironomids were used as indicators of changes in trophic level and salinity. It took 40 years for the method to develop and establish. It was between 1980s and 1990s that scientists started to use chironomid assemblages as a proxy for climate, in particular summer temperatures (1). A notable disadvantage of the method, however, is the time it takes to prepare the microscope slides and identify fossil head capsules. One has to hand pick each individual tiny skull from the sediments before mounting them on the microscope slides.

  1. Oxygen isotopic composition of chironomid remains tracks that of past lake water

A more recent paleoecological application utilizes the chemical composition of head capsules (my current learning process!). They are made of chitin (C8H13O5N), an organic compound with a similar function as the keratin in our hair and nails. The isotopic composition of carbon, oxygen or nitrogen in the chitinous head capsules can be used to reconstruct changing environmental conditions as well. The δ13C and δ15N reflect their diet (4), and can be used to study sources of organic matter, and past food webs (5). Some genera (Chironomus, Stictochironomus and Propsilocerus) absorb C from methane, and have been used to infer past methane abundance and cycling (5, 6).  We are interested in the δ18O, as 70% of it comes from the water the larvae grow in (7). Water stable isotope ratios (δ2H and δ18O) can give us an insight into past hydrological dynamics affecting the lake, more specifically precipitation amount and source, as well as summertime evaporation, both of which also control lake levels and catchment dynamics. Thus, we can study hydroclimatology through changes in the isotopic composition of past lake water recorded in the head capsules.

In our present study, the lake area is considerably smaller than the catchment, which usually results in a short water residence time. Because of it, we can assume that the isotopic composition of lake water is sensitive to changes in regional hydroclimate resulting in e.g. higher or lower lake levels and changes in seasonality. In our project more broadly (Beyond the shore: sea-ice change and lake ecosystems in the Arctic or SLEET, funded by the Academy of Finland), we are studying how changes in past sea-ice cover influences lake ecosystems through the hydrological cycle.

Three chironomid head capsules floating on the sediments, ready to be picked up and cleaned.

The road to retrieve the isotopic composition of the past lake water from chironomid head capsules requires fine motor coordination and perseverance. Before measuring the δ18O from the fossils, I first have to separate them from the rest of the sediments and clean them. This is how I spend my days at the moment: I sit in front of the microscope, and with a pair of sharp tweezers and patience, I inspect the rinsed sediment in search of as many head capsules as I possibly can find. For producing a summer temperature reconstruction based on species assemblages, typical studies count and identify between 50 and 200 head capsules per sample. For measuring the oxygen isotopic composition, however,  we need a minimum of 80 µg of head capsule mass, which sounds like a very small amount but requires from 100 to up to 800 head capsules and fragments depending on the size. In addition, the abundance of remains in the sediments can vary greatly. It is a long journey, and I anticipate that the results we will get will feel equally rewarding.

Lilia is a PhD student who listens to podcasts while working on the microscope.

NOTE: Isotopes are atom variations of the same element. They have the same number of protons and electrons, but a different number of neutrons, which results in mass differences among the isotopes. Usually some isotopes are more abundant than others, for example 99.76% of the oxygen in nature is 16O, while only 0.20% is 18O. The delta-value notation is the ratio between the less common isotope, and the most abundant, and to a standard value. Because these values are still too small, they are reported as per mil. We can use stable isotopes because of their mass differences. During physical and biological processes the light and heavy isotopes fractionate, they separate. Take boiling water as an example, it takes less energy to evaporate water molecules with light  isotope 16O, than with heavier isotope 18O.

References:

  1. Brooks SJ, 2006. Fossil midges (Diptera: Chironomidae) as palaeoclimatic indicators for the Eurasian region. Quaternary Science Reviews 25: 1894–1910. https://doi.org/10.1016/j.quascirev.2005.03.021
  2. Gams H, 1928. Die Geschichte der Lunzer Seen, Moore und Wälder. Vorläufige Mitteilung. Internationale revue der gesamten Hydrobiologie und Hydrographie 18:349–387.
  3. Goedkoop W, ÅKerblom N, Demandt MH, 2006. Trophic fractionation of carbon and nitrogen stable isotopes in Chironomus riparius reared on food of aquatic and terrestrial origin. Freshwater Biology 51:878–886. https://doi.org/10.1111/j.1365-2427.2006.01539.x
  4. Heiri O, Schilder J, van Hardenbroek M, 2012. Stable isotopic analysis of fossil chironomids as an approach to environmental reconstruction: state of development and future challenges. Fauna norvegica 31:7–18. http://dx.doi.org/10.5324/fn.v31i0.1436
  5. van Hardenbroek M, Heiri O, Grey J, Bodelier PL, Verbruggen F, Lotter AF, 2010. Fossil chironomid δ13C as a proxy for past methanogenic contribution to benthic food webs in lakes? Journal of Paleolimnology 43:235–245.
  6. Walker IR, 2006. Chironomid Overview. Elsevier, Cambridge, UK.
  7. Wang YV, O’brien D, Jenson J, Francis D, Wooller M, 2009. The influence of diet and water on the stable oxygen and hydrogen isotope composition of Chironomidae (Diptera) with paleoecological implications. Oecologia 160:225–233.
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How to tend to your research (and motivation) during a pandemic: our view of the past year

by Lilia Orozco

It is almost a year since the COVID-19 pandemic spread globally, but the final repercussions for science will be realized in the years to come. Travel restrictions canceled most planned fieldwork, conferences and research visits, while social distancing changed the way we communicate, plan our activities and interact. How we, as a scientific community, confront the new circumstances has been a subject of conversation from the beginning (1-3).

On March 16, 2020, the Universities in Finland were shut down. Since then, our research group has been managing projects and thesis work from a new angle. I started my PhD research on past northern lake ecosystems in November 2020, amid the exceptional situation. I was prepared for the home office and the uncertainty in field and lab work plans. It helped me to focus on what I can do rather than what I cannot. A pandemic-suited mindset might be easy to set at the beginning of a project, but how has it been for those who made their plans prior to COVID-19? I asked our group.

Most of us had to make arrangements. Maxime Courroux, a Master’s student studying sub-arctic lakes, explains:

“A Master’s thesis is a relatively short project. But within a year, I had to change my topic, re-plan my field schedule, and manage to finish everything on time. While this wasn’t a walk in the park, the shared struggle with peers has led to a lot of support. Nothing went as expected, but it was still fun.”

For Tiia Luostarinen, PhD candidate studying microscopic sea-ice organisms, the closure of universities, and even countries, meant leaving laboratory analyses at a short notice.

“When the pandemic started to spread in Europe, I was in Denmark for some lab work but was supposed to travel back home in a couple of days anyway. When the Danish government announced that they are closing their borders, I changed my flights and returned to Finland. It was hard to miss saying proper goodbyes to everyone in Copenhagen.”

Despite the boost in discoveries and publications about and COVID-19 (4, 5) in the past year, natural sciences looking into equally topical global challenges, e.g. climate change and environmental degradation, have not had that luck (6). Restrictions have forced scientists to re-think their projects and plans. The University of Helsinki closed its facilities, but we have been able to carry out essential lab work under strict regulations.

Maija Heikkilä, the principal investigator of both currently active Academy of Finland funded projects, faces these circumstances head-on:

“Getting a research project funded is always a thrill, and in all honesty, having another research project launched during the global pandemic was equally exciting. There are new questions to be answered, new people to be hired, and due to the pandemic, new implementation plans to be made. This is much easier at the very beginning of the project than in the middle of it, but we have managed all our work rather brilliantly. Our University has been strict but prioritized science where possible.”

The University of Helsinki allowed a field trip on our Master’s level course Past environmental change in January 2021, because it was held outdoors with safe distances. Senior researcher Jan Weckström giving a demonstration on sampling methods. Maxime and Lilia were teaching assistants.

Collaboration and exchange of ideas are focal to any research. The social restrictions have forced us to use different technologies (who could have imagined the now-so-routine ZOOM coffees a year ago!). The new ways of communicating are not always ideal, in particular if you have just arrived in a new country. This is the experience of Ana Lúcia Lindroth Dauner, the new postdoc researcher in the team working on integrating and combining paleoecological data. Ana has not even met everybody in the group in person.

“Besides conciliating the time between academic and domestic work, the main issue I have had in starting to work on a project in the midst of the pandemic is the lack of personal contact. The pandemic makes it difficult to get to know new people and, therefore, to share thoughts and ideas.”

Ana shared a view to her home office.

We have all coped with the situation that started one year ago in different ways. We have had to find a balance between life and work, transform our homes into offices, and accept new realities that we did not expect. For Master’s student Meri Mäkelä, whose thesis unravels past ecosystem changes in an arctic fjord, staying motivated has helped her finish her project.

“In February 2020 I definitely couldn’t predict that after a year I would still be finishing my Master’s thesis surrounded by the pandemic. No doubt that the pandemic has slowed down my thesis project, but to be honest, my enthusiasm to left no stone unturned should be blamed more. At least I have learned to make less overly optimistic timetables for my projects to come – I hope.”

Confinement is not ideal for everyone, but after a year of this reality, we have modified our practices. Tiia has learned to appreciate the time at home.

“If you would have asked me if I liked working from home a year ago, the answer would’ve been a definite no. But this situation has at least taught me to appreciate the quietness and flexibility of working from home. And obviously, the better coffee.”

Like Tiia, Maija profits from the advantages of telecommuting and stays optimistic.

“The lack of commuting and traveling has brought a new sense of tranquility to daily work tasks and challenged me to develop new ways for team building. I am positive and face challenges that are much smaller than the responsibility of an individual to take part in fighting the global pandemic.”

Indeed, while we look forward to resuming fieldwork and in-person interaction as soon as it is safe, it is good to keep things in perspective. Despite our differing experiences and perspectives from the past year, everyone has surely mastered one thing – to adapt.

—-

Lilia Orozco is a PhD student who celebrates picking the first fossil remains in her lake sediment samples.

List of references:

  1. Clay RA (2020, March 19). Conducting research during the COVID-19 pandemic. http://www.apa.org/news/apa/2020/03/conducting-research-covid-19
  2. Pain E (2020, April 17) How early-career scientists are coping with COVID-19 challenges and fears. Science Careers.
  3. Kupferschmidt K (2020, February 26). A completely new culture of doing research. Coronavirus outbreak changes how scientists communicate. Science News. 
  4. Science in the Wake of the Pandemic: How Will COVID-19 Change the Way We Do Research? (2020). Molecular cell 79:9–10. https://doi.org/10.1016/j.molcel.2020.06.024
  5. Palayew A, Norgaard O, Safreed-Harmon K, Andersen TH, Rasmussen LN, Lazarus JV (2020). Pandemic publishing poses a new COVID-19 challenge. Nature Human Behaviour 4:666-9. https://doi.org/10.1038/s41562-020-0911-0
  6. Bian SX, Lin E (2020). Competing with a pandemic: Trends in research design in a time of Covid-19. Plos One 15:e0238831. https://doi.org/10.1371/journal.pone.0238831