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Old data series provide new answers about brown water

Last changed: 25 November 2020
Professor Emma Kritzberg at Lund University

Many scientists have tried to find out why the water in lakes and streams is becoming browner. At Lund University, limnologist and newly appointed professor Emma Kritzberg found interesting clues in historical data material, including from the Swedish National Forest Inventory – and they pointed in a new direction.

In a prevailing hypothesis, the so-called “brownification” (the gradual change in the colour of water in certain lakes and streams) is explained by biogeochemical processes in the soil, which were affected by the high sulphur deposits that occurred in the 1970s and 1980s. The hypothesis is that the recovery of the soil after acidification has caused increasing levels of dissolved organic matter (DOC) to “brown” the water in certain lakes and streams. 

“The acidification made us aware of the large-scale airborne environmental degradation and contributed to the expansion of environmental monitoring during the 1970s and 1980s. In the decades since then, we have seen the colour intensify, and the conclusion that has been drawn is that the water was unnaturally clear back then, when the pH was low,” explains Emma Kritzberg.

The increasingly brown colour was assumed to be due to the fact that the acidification-affected soil was slowly recovering. Mechanistic studies have indicated that there is such an effect – the more acidic the soil water, the less soluble the DOC. The reduction in acidification is one factor behind brownification – another being climate change, which contributes to faster degradation of organic matter and increased transport from soil to surface water.

A treasure chest at SLU

Since a great deal of data collection was initiated during the era of acidification, few analyses include water quality data from the years prior to that period. Emma Kritzberg was looking for a way to go further back in time. In connection with another research project, she had come into contact with SLU’s environmental analysis data for lakes and began to realise what a treasure chest they constituted.

“I was completely bewitched. I sat up at night and couldn’t stop plotting different variables from environmental analysis data,” says a visibly enchanted Emma Kritzberg. “All the research on the brownification had to do with DOC leaking from the soil. But here I saw that iron had also increased. What was the explanation for that?”

The increasing levels of iron aroused Emma Kritzberg’s curiosity, and she asked herself if it might be possible to find out what watercourses and their surrounding natural environments looked like before acidification.

Chance contributed

In a successful research study, the pieces of the puzzle can find their way to the researcher in unexpected ways. With evident fascination, Emma Kritzberg describes how a haphazard meeting with an engineer at a waterworks led her to a data series on the water quality in the Lyckeby drinking water supply that stretched all the way back to the 1940s. Furthermore, after an interview in Sydsvenskan newspaper she was contacted by a researcher at SLU (Matts Lindbladh) who tipped her off about compilations of the Swedish National Forest Inventory’s data from the same area and time period.

Suddenly it was possible to put a new piece of the puzzle in place – one that indicated that the increased distribution of spruce forests in southern Sweden probably had a greater impact on water quality than previously thought. In this part of Sweden, the coverage of spruce has risen from 15% before the turn of the last century to 75% today.

The conclusion about the importance of spruce for water has been received surprisingly well in the scientific community, despite major investments in acidification research and measures to address acidification, says Emma Kritzberg.

“There’s something positive about this insight – namely, that this is a problem that we are able to influence. Because even if landowners decide to continue growing spruce in southern Sweden, hopefully local measures – such as deciduous forests in a zone along the waterways – can reduce brownification.”

Brownification is an urgent issue, because it entails increased costs to society to purify drinking water. No one wants the water coming out of their tap to be brown and smelly. This is particularly important in those parts of the country where lakes are used as water supplies and where the problems of brownification are most evident.

Sweden shares its data

This research is unlikely to be the last word on the causes of brownification, but Emma Kritzberg will continue to dig for gold in SLU’s environmental monitoring data. She recounts that international researchers tend to express jealousy when she talks about her research, which is based on SLU’s open data. The combination of long data series and openness is unique to Sweden, and for those who come from the competitive scientific community where people hoard their collected data, it may seem improbably generous. Emma herself once shared this territorial mindset.

“The first time I published an article based on data I extracted from SLU’s data, I was almost ashamed. Should I really be listed as the author when SLU had done all the heavy lifting?

The main purpose of environmental monitoring is to monitor changes in the environment and our natural resources, and it is based on society’s need for a foundation for decisions on legislation, support measures and instruments. After decades of stubborn data collection, the series is starting to grow so long that the information is becoming increasingly relevant to researchers who, like Emma Kritzberg, are finding new uses for the data.

Social investment bears fruit

Most research projects have a short time horizon and funding for research infrastructures is limited. Here, data from natural resource and environmental analysis can play an important role, and society’s investment in data collection can bear fruit in several ways.

Emma Kritzbergs has straightforward advice for researchers who are curious about environmental analysis data and wonder how they can be used.

“Talk to the people behind the scenes, who know how the data were collected. Chances are you will be greeted with enthusiasm!”



Forest statistics.

Growing stock for different tree species by Year, County, Table contents and Tree species) 

Number of stems by tree species and diameter class (>=10 cm). All land use classes (1923 - date) by Year, County, Table contents, Tree species and Diameter class (cm) 

Volume hard dead wood, >=10 cm i diameter and 'suitable for firewood' (1923 - date) by Year, County and Table contents)

Area of comparible land use classes (1923 - date) by Year, County, Table contents and Landuse class

Productive forest area for different age classes by Year, County, Table contents and Age class

THe same information is available in a format suitable for visualisation.

Läs mer om förutsättningar, definitioner och jämförbarhet över tid. (Swedish).

If you can't find what you are looking for, please contact Swedish National Forest Inventory that offers help with customized analyse and data extraction.

Miljöövervakningsdata för sjöar och vattendrag kan hämtas i databasen Miljödata-MVM. (Swedish only)

Read more about the data host for lakes and watercourses.

Research at SLU on brownification

At the department of Aquatic Sciences and Assessment, SLU, there is also research into the brownification of Swedish lakes, in collaboration with among others Emma Kritzberg. One important focus area is the effect of brownification on drinking water.



Anna-Lena Axelsson, researcher
Dept. Forest Resource Management, SLU, +46(0)90-786 85 91, +46(0)70-376 21 71