Lena Kautsky. Foto: Eva Dalin
 
 
The sun is shining, it is time for lunch and one of my PhD students asks me if I would like to join them for a swim in Brunnsviken bay. I have been here at the Department of Botany since 1970, next door to Brunnsviken, which is connected to the Baltic Sea through the Ålkistan canal and Värtan bay. After all these years, my first spontaneous reaction is still, “Yuck! No, absolutely not – it is a green, smelly algae soup”. And I am instantly taken back to when I began my PhD studies in 1970.
 
So what was the problem? The lack of oxygen underneath the ice caused fish to die and float ashore. The reed belt was spreading along the shores, and the water turned green from algal blooms in the summer. The cause of this negative development was that untreated sewage from Solna was released into Brunnsviken, and my task as a PhD student was to study what happened in Brunnsviken when the pollution was stopped in 1970.
 
Could it ever become clean? Without algal blooms? And with water so clean that I can see the bottom when I step into the water? During my PhD studies, I performed many chemical analyses of phosphorus and nitrogen, sediment and phytoplankton samples, which led to many, many long hours at the microscope. The finding of diatoms in the bottom samples showed that Brunnsviken, just like the Baltic Sea, has gone through various stages over the millennia.
 
Brunnsviken could be likened to a miniature Baltic Sea. Until 640 years ago, the bay was connected to the Baltic Sea. Due to land elevation, the bay was then cut off and became a lake for about 290 years. As early as more than a century ago, August Blanche wrote in “Hyrkuskens berättelser” of how bad the water was and of “Brunnsviken’s stagnant water, where the wave is like green soup and the fish swims dead towards the muddy beach”. The cause of the heavy algal blooms and the oxygen depletion that caused the fish to die was that the bay was already polluted with sewage from Stockholm City.
 
The first step to improve the water environment of Brunnsviken was taken in 1863, when it was reconnected with the Baltic Sea through the construction of the Ålkistan canal. However, more and more untreated sewage was released into the bay from Solna. This pollution was not stopped until 1970, upon which the salinity of the surface water rose from 2 to 3 parts per thousand. Even this minor change meant that I was able to find several species of diatoms that Astrid Cleve Euler described in her studies of the bay in the early 1920s as being characteristic of this salinity before the addition of fresh water from Solna lowered it. The water quality improved gradually, with less algal blooms, clearer water and no oxygen depletion or fish kills.
 
So, roughly 40 years later, the answer to the question from my PhD students if I would like to join them for a swim in Brunnsviken is simple: “Sure, I would love to go for a dip!”
Only Stockholm University is located in a national city park with a bay where I can go for a swim during lunch! A bay that was sung about as early as 220 years ago by Carl Michael Bellman in “Fjäril vingad syns på Haga” and “Se, Brunnvikens små najader höja sina gyldne horn, och de fräsande kaskader sprutas över Solna torn”.
 
Today, many of us can enjoy a bath or go for a walk around this historical Baltic Sea bay, where dragonflies and butterflies will hover above the glistening surface on a beautiful summer day, or go skating. And when the ice melts, the water will not smell like rotten eggs.
 
Narrator: Lena Kautsky