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Monitoring compared with paleolimnology: implications for the definition of reference condition in limed lakes in Sweden.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2008 (English)In: Environmental Monitoring & Assessment, ISSN 0167-6369, Vol. 146, no 1-3, 295-308 p.Article in journal (Refereed) Published
Abstract [en]

Surface water acidification was identified as a major environmental problem in the 1960s. Consequently, a liming program was launched in Sweden in the 1970s. The primary purpose of liming is to restore conditions that existed prior to acidification. To reach this goal, as well as achieve ‘good status' (i.e. low levels of distortion resulting from human activity) in European freshwaters until 2016 under the European Union Water Framework Directive, lake data are required to define reference conditions. Here, we compare data from chemical/biological monitoring of 12 limed lakes with results of

paleolimnological investigations, to address questions of reference conditions, acidification, and restoration by liming. Using diatom-based lake-water pH inferences, we found clear evidence of acidification in only five of the 12 lakes, which had all originally been classified as acidified according to monitoring data. After liming, measured and diatom-inferred pH agree well in seven lakes. The sediment record of three of the five remaining lakes gave ambiguous results, presumably due to sediment mixing or low sediment accumulation rates. It is difficult to determine whether liming restored the lakes to a good status, especially as some of the lakes were not acidified during the twentieth century. In addition to acid deposition, other factors, such as natural lake and catchment ontogeny or human impact through agricultural activity, influence lake acidity. This study shows that monitoring series are usually too short to define reference conditions for lakes, and that paleolimnological studies are useful to set appropriate goals for restoration and for evaluation of counter measures.

Place, publisher, year, edition, pages
2008. Vol. 146, no 1-3, 295-308 p.
URN: urn:nbn:se:umu:diva-11340DOI: doi:10.1007/s10661-007-0081-9PubMedID: 18058250OAI: diva2:151011
Available from: 2008-12-16 Created: 2008-12-16Bibliographically approved
In thesis
1. A paleolimnological perspective on liming – implications for defining reference conditions in Swedish lakes
Open this publication in new window or tab >>A paleolimnological perspective on liming – implications for defining reference conditions in Swedish lakes
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Using paleolimnological techniques, I have studied surface-water acidification and the effects of liming in Swedish lakes on a decadal to millennial time-scale. The overall objective was to contribute to the discussion on the fulfilment of goals within the Swedish liming program. One of the main goals of this program is to restore lakes to natural or nearly natural conditions, i.e. to a reference condition as termed in the EU Water Framework Directive. In this context, a key issue is to define reference conditions. This is a central theme of my thesis, as lake sediments offer a unique way to study past lake conditions.

Past lake-water acidity of 12 reference lakes in the Swedish liming program (ISELAW) was determined using diatom analysis of sediment cores. Pollen, lead, and flyash from coal/oil combustion were used as indicators of impact from land use and atmospheric pollution. A general trend in these lakes is an initial decline in pH after lake formation due to natural soil processes, which was then followed by rather low pH values (pH 5.3-6.5). In six of the lakes pH increased as a result of expansion of agriculture (burning, forest grazing) 2000 to 1000 years ago. Local mining and long-range airborne pollution have also impacted the lakes since medieval time. These results show that the conditions of the study lakes were not natural prior to industrialization and recent (20th century) acidification.

The ISELAW lakes were selected on the basis of representing typical limed lakes, and they have been limed and monitored since at least the 1980s. A comparison of chemical/biological monitoring data and the paleolimnological data gives somewhat diverging results. Most of the monitoring data suggest that the lakes were subjected to acidification during the 20th century, but the paleolimnological data can only identify clear evidence of acidification in five of the 12 lakes, hence, all lakes were probably not recently acidified. According to conclusions from monitoring the lakes have recovered following liming. The paleolimnological data give a more complex picture and three different responses have been identified: 1) a return to a diatom composition found in the lake one hundred to several thousand years ago; 2) very small shifts in the diatom composition; or 3) a diatom composition previously not found in the lake. The latter response raised the question whether liming can cause an unnatural diatom community. A comparison of diatoms in surface sediment samples of 31 limed lakes with pre-industrial reference samples from 291 lakes showed that liming does not create an unnatural diatom composition. These results illustrate that the goals for liming were not reached in all of the limed lakes, and that paleolimnology can play an important role for assessments of acidification and liming. The comparative study also highlights the importance of designing monitoring programs that can produce reliable and long data series.

Given the results of the paleolimnological investigations, it is obvious that we cannot assume that the 19th century represented a natural or near natural state, and thus is a realistic reference conditions. Natural long-term lake development and previous land-use impacts need to be considered in defining reference conditions. Neither can we disregard the fact that humans always will impact nature. Although paleolimnological studies are time consuming, I believe that they could be simplified to the extent that paleolimnology could become a routine method for environmental management.

Place, publisher, year, edition, pages
Umeå: VMC, KBC, Umeå University, 2009. 14+4 papers p.
Acidification, Liming, European Water Framework Directive, Reference condition, Diatoms, Paleolimnology, Monitoring, Lake sediments
National Category
Earth and Related Environmental Sciences
Research subject
Earth Sciences with Specialization Environmental Analysis
urn:nbn:se:umu:diva-20583 (URN)978-91-7264-761-9 (ISBN)
Public defence
2009-04-24, KB3A9 (Lilla hörsalen), plan 3, KBC-huset, Umeå universitet, Umeå, 10:00 (English)
Available from: 2009-03-31 Created: 2009-03-23 Last updated: 2009-03-31Bibliographically approved

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