Funded by LBAYS: Fish, food webs, and mercury – a boreal experience

Alexander Piro, researcher at Lammi Biological Station, delves into the enigmatic dynamics of mercury in Finnish ecosystems. Unraveling its journey through fish and food webs, his PhD explores seasonal fluctuations, species-specific accumulation, and regional variances.

We have a long history and experience with mercury, with it having been mined and utilized by numerous ancient civilizations in Egypt, China, Rome, and elsewhere. More recently, mercury is more often recognized for its severe neurotoxicity. Despite the long history we have with mercury, there remains much we don’t know about it and its dynamics in the environment. My PhD is focused on how mercury fluctuates in fish and throughout food webs across the Finnish landscape over time.

While fluctuations in seasonal mercury concentration have been detected over the course of the year in some fish, whether or not this is consistent in many species remains to be seen. The same could be said about the accumulation of mercury in fish over time. In the broader food webs of lakes, it is also unclear whether the movement of mercury up the food chain changes throughout the year. We also don’t have great knowledge on whether there are differences in how mercury moves through the food chain in a variety of lake types in different regions.

That’s where I come in at Lammi Biological Station on the shore of Lake Pääjärvi. My work at Lammi primarily consists of two parts: field and lab. 

In the field, I work with a team to collect invertebrates from the shoreline as well as from the open water using different types of nets. We also collect algae, aquatic plants, and phytoplankton, but this depends on the season. We always collect fish from the shore area, open water, and deep areas of lakes using a series of gillnets.

In the winter, the game changes somewhat. We do all of this again, while also having to drill ice holes, cut ice blocks, and pull ropes under the ice to set nets in freezing temperatures to get the samples we want. Winter work is more physically and logistically taxing, but these “inconveniences” create a type of research niche to exploit, as not nearly as much field work for research is conducted in the winter as in the summer.

Once we get back in the lab, the work consists of cleaning, sorting, and storing the samples collected from the field, while also dissecting a massive number of fish. We then completely dry the samples and crush them to a powder before running them through a mercury detection machine, which gives us the concentration. Another part of my project was to measure stable isotopes of carbon and nitrogen in organisms throughout the food web. To do this required more measuring of dried samples and prepping them for stable isotope analysis at the University of Jyväskylä. This scope of work is very important because carbon gives us an idea of what kind of habitats the organism is using, and the nitrogen shows us where the organism stands in the food chain.

We found that many species were significantly higher in mercury in the winter and spring than in summer and autumn, and that the concentration was closely linked to environmental conditions and physical characteristics of the fish. It was also clear that all species accumulated mercury in their muscle at a higher rate during summer and autumn compared to spring and winter. We also found that the rate at which mercury moves up through the food web does not seem to significantly change throughout the year, though using different methods to measure this process predicted significantly different mercury concentrations at the bottom of the food web – suggesting that how this process is classically measured requires refinement. This work is currently under review.

Working at Lammi has been intensive and primarily focused on collecting and processing thousands of samples. I have been working at Lammi full time for three years and have had the chance to work with some incredible and motivated people. The interns, students, and trainees that have come through the aquatics team during my time here have been absolutely critical to the work getting done. These folks are the backbone of the vast majority of the work that gets done at the station, not only on the aquatics team, but on all the teams here. I am very grateful to the Lammi Biological Station and LBAYS for providing the facilities and support necessary to make this project successful in conducting this work.

Piro, A.J., Taipale, S.J., Eerola, E.S., Megyeri, E., Kahilainen, K.K., 2024. Does mercury biomagnification in a boreal lake food web vary year-round? – A comparison using bulk δ15N and compound-specific δ15N of amino acids. Under Review

Piro, A.J., Taipale, S.J., Laiho, H.M., Eerola, E.S., Kahilainen, K.K., 2023. Fish muscle mercury concentration and bioaccumulation fluctuate year-round – Insights from cyprinid and percid fishes in a humic boreal lake. Environ. Res. 231, 116187.

More research funded by LBAYS