Eighty-year-old findings to help solve water mystery

82 years after his death, limnology superstar and the first professor in this field in Lund and the world, Einar Naumann, may have helped solve the riddle of why lakes become brown. With the help of Naumann’s and his students’ work dating back to the 1930s, senior lecturer Emma Kritzberg has created a data series that fill a gap of 50 years.

Emma Kritzberg

Emma Kritzberg

In Sweden and many other countries in the northern hemisphere, one of the major water problems is so-called ‘brownification’ – a phenomenon that involves clear water in creeks, streams, rivers and lakes becoming brown. No one knows why for certain, but Lund biologist Emma Kritzberg emphasises that land use is a major factor. If this is true, it is probably possible to reverse the trend.

Some lakes are naturally brown. The reason is that they are surrounded by marshes and mosses which release organic material. But many lakes can be found in other types of environments. In the 1980s, when acidification was at its worst in Sweden, we began measuring the quality of our water. In the early 2000s, the data series was sufficiently long and the research took off. The studies showed that many lakes are rapidly becoming browner.

“Since we haven’t had any data series prior to the 1980s, however, we didn’t know what the colour of the lakes were before the acidification”, says Emma Kritzberg.

There are three main tracks in the researchers’ search for explanations as to why lakes and other water bodies are turning brown, two of which have been particularly in focus over the years: the hypothesis that brownification is a recovery from acidification and thus a return to a more natural state, on the one hand, and, on the other, the theory of the impact of climate change, with higher temperatures, longer growing seasons and therefore an increased amount of organic material in the drainage basins.

Emma Kritzberg believes that the third track – land use – is of great importance. According to her, the colour of the water in a lake is strongly linked to the amount of coniferous forest in the drainage basin. The more coniferous forest, the browner the water.

However, land use has been dismissed by most researchers as the hypothesis has not been scientifically proven. This is because the data series only dated back to the 1980s. That is, until now, when Emma Kritzberg has taken it upon herself to study the data from Einar Naumann and his students from various lakes around the limnological field station in Aneboda, Småland. In addition to studying the compiled information from the old books, she has personally visited the lakes in the region and collected her own water samples.

“Now there is a dataset on water colour from 50 different lakes from the 1930s and onwards. It is clear to me that before the acidification, the water was clearer than it is today.”

Furthermore, the compilation of information indicates that the brownification of the water began long before the acidification process started.

“This means that brownification is not a return to a more natural state. Instead, I believe that land use is a very important factor.”

The conclusion is based on the fact that the farmlands by the lakes around Aneboda drastically changed at the turn of the 20th century. Before the 1900s, about 15 percent of the land was covered by spruce. Today, the number has increased to 65 percent. This change in land use is typical for all of northern Europe, and was caused by depopulation and the introduction of fertilisers.

“We know that the coniferous forests produce browner water. The reason why the colour change occurs so long after the planting is probably that it takes several decades for organic soil layers to form”, says Emma Kritzberg.

If her theory is correct, it may be possible to reverse the trend.

“So far it’s speculation, but it seems likely that if you plant deciduous trees rather than conifers in the areas closest to the surface water, it could eventually lead to clearer water.”

Text: Jan Olsson

The World Water Day will take place on 22 March. Vattenhallen Science Centre will highlight the various aspects of the world’s most important natural resource. Lund University is conducting water research in several areas, one of which is why lakes that were once clear turn brown.