What are diatoms?

Last night our neighborhood got together to take care of the joint property unit (is this the appropriate term for städkväll i samfälligheten?). I was mentioning to my neighbor – also active as writer on this blog – that I was supposed to blog during the coming weeks, and she suggested me to write about my research topic. “What are you working with?”, and I answered “diatoms, sediment and long-term environmental change” – “What are diatoms? This seems way more interesting than the long-term thingy”. Obviously, this is a very adequate opportunity to present diatoms, my favorite environmental indicators, to a wider audience.

Diatoms exist in literally everywhere where you can find water, for example in streams, rivers, lakes, and the oceans, but also in the soil. They are a major group of unicellular algae with important ecological function for oxygen production and food webs. In a typical lake in northern Sweden, you will find millions of diatoms in one liter of water, without recognizing them by eye. And, as you can see on the picture above, they are just stunning! Each diatom has a characteristic, beautiful ornamentation that is only visible using a light microscope. To fully resolve all structures, scanning electron microscope techniques are needed. The diatoms above, Cyclotella, live in our study lake Nylandssjön (Nordingrå), and have a diameter of a few micrometers. Still reading? Then you should go for a more detailed description, for example  https://en.wikipedia.org/wiki/Diatom

Why studying them? In order to understand long-term environmental changes, we are depending on environmental archives and indicators that can tell us something about the conditions that prevailed in prehistoric times, before instrumental data are available. And diatoms fulfill two of the major criteria that are important. First, they are sensitive to the ambient water quality (temperature, salinity and nutrient levels), and record environmental conditions simply through their presence. Secondly, their cell walls that are made of silica may persist in for very, very long time. A rather special application field of diatoms is forensic limnology. The presence of characteristic diatom colonies on clothes or in tissue sample of suspects or victims are matched against samples from the crime scene location. As they diatom assemblage is unique to every lake or pond, a close match of diatom assemblage can provide evidential support.

Not only are the surroundings in our neighborhood now tidy after the long winter in northern Sweden. More important, I got by chance a topic for the first blog post. Thanks, Bodil!

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