Lake Sysmäjärvi – taking a closer look to mining impacted lake
(This blog post was originally published on May 10th 2021 at https://www.uef.fi/en/article/blog-winter-limnology-in-north-karelia)
Text: Hannu Nykänen & Helena Jäntti | Photo: Carlos Palacín
January, minus 15 degrees Celsius. The sun is about to come up. There is snow on the ice that occasionally collapses when you step on it. Underneath the snow, there is water. I am trying to step into the footmarks that Helena has left behind. Leather shoes were not the right choice for today, there is just too much water. Live and learn. Pyry went first, alone, driving the snowmobile. Sledging is difficult in watery-snow slush, and the snowmobile must be left on the islet. In the slush, heavy work snowmobile would no longer come off because of the frost. “It’s acidic!”, Pyry shouts and takes a photo from the YSI-meter screen.
We are collecting water and sediment samples from Lake Sysmäjärvi in Outokumpu, North Karelia, to find out why lake water acidification is taking place during spring. Even when it is not spring, the water is already acidic. Our wet toes are starting to freeze. Tar black sediment can be collected with sediment grabs, but water sampler, Limnos, freezes after getting it out of the water the first time. The trip was not supposed to be this difficult for experienced scientists. Usually samples are collected during open water season or during spring when the sun gives warmth.
We came to Lake Sysmäjärvi to investigate why water quality monitoring shows signs of acidification. Everyone can view the officially collected monitoring data from an open database called Hertta, maintained by the Finnish Environment Agency. Measurement data related to Lake Sysmäjärvi has been collected since 1968. There are indications regarding water acidification, however, the information is fragmented, and it must be refined into a more comprehended form: figures and tables. This data and mining the data will be examined in a master thesis at the University of Eastern Finland, Joensuu campus.
Outokumpu, Vuonos, and Keretti mines produced copper ore and concentrate from 1910 to 1989. What is the problem then with Lake Sysmäjärvi, a few kilometres from the mine? We must now go back even further in history, quoting Peltonen et al.’s (2008) article: ‘Outokumpu-type Cu-Co-Zn-Ni-Ag-Au sulfide formation was formed around 1.95-1.88 billion years ago’. The sulfide minerals were formed when hydrogen sulfide oozing from the oxygen-free seabed encountered the metals that leached from the soil to the sea. The same phenomenon is applied also in mouthwashes – the zinc chloride added to the mouthwash binds smelly hydrogen sulfide and forms an odorless sulfide mineral. What happens when sulfide mineral is mined, grinded, enriched and disposed? If the mineral contains neutralizing rock species, acid release does not occur in harmful measures. However, if there are no neutralizing components in the mining waste, contact with oxygen, water, and bacteria will begin releasing sulphuric acid and metal ions into the surrounding waters. This results in acidic run-off called acid mine drainage (AMD).
Why were we on the lake in January in such a cold weather? When the snowmobile belts are filled with slush that freezes like the feet of a researcher who chose the wrong shoes? The aim was to find out how the process leading to acidification works in Lake Sysmäjärvi, and furthermore, is the acidification a result of the chain of events related to piles of mine tailings. For this reason, oxygen concentration, acidity, and temperature were measured in the lake as background information for a master thesis study on sediment processes. The sediment processes are studied under controlled laboratory conditions at the University of Eastern Finland, Kuopio campus.
In the laboratory, the sediment microbes were killed by heat in some of the samples. This allowed us to separate effects of chemical and microbiological processes on acid formation. By incubating the sediment without oxygen, we imitated the situation where there is no oxygen in the water and anoxic processes occur under the ice. Anoxic conditions under the ice are quite common in shallow and nutrient rich lakes because oxygen-consuming decomposition processes continue throughout the winter, while less oxygen dissolves from the atmosphere into water due to the ice cover. By adding air, a situation corresponds to overturn during spring, when the water profile is uniformly cold and oxygenated. The surface water mixes with anoxic water and causes acid release. Adding sugar to the sediment sample mimics the growth of algae in lake and the effect of increase of fuel to microbiological processes. Also, nutrients and both, oxidized and reduced forms of iron were measured. But why measure iron when investigating the effects related to a copper mine? Because, actually, iron represents all bivalent metals in processes, and iron chemistry and microbiology are best known.
On the way home, back to Kuopio, our toes warmed up and the shoes slowly dried. It seems that the sediment behaved as expected, however the role of microbes, which has not been traditionally determined in these studies, is more significant than expected. The further processing of the results is in the final stages and the thesis is about to be completed. The ice melted from Lake Sysmäjärvi during week 16. The shores are getting greener. We did an additional sampling of water column just before 1st of May, May Day. More outcomes about that trip in the next blog post.
Peltonen, P., Kontinen, A., Huhma, H., Kuronen, U. (2008) Outokumpu revisited: New mineral deposit model for the mantle peridotite-associated Cu–Co–Zn–Ni–Ag–Au sulphide deposits. Ore Geology Reviews, 33, 559–617.
UEF Water programme is funded by Saastamoinen foundation, Wihuri foundation and Olvi foundation.