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A paleolimnological perspective on liming – implications for defining reference conditions in Swedish lakes
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science. (Environmental Change Assessment)
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.
Keyword [en]
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
Identifiers
URN: urn:nbn:se:umu:diva-20583ISBN: 978-91-7264-761-9 (print)OAI: oai:DiVA.org:umu-20583DiVA: diva2:209082
Public defence
2009-04-24, KB3A9 (Lilla hörsalen), plan 3, KBC-huset, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2009-03-31 Created: 2009-03-23 Last updated: 2009-03-31Bibliographically approved
List of papers
1. Liming placed in a long-term perspective: a paleolimnological study of 12 lakes in the Swedish liming program
Open this publication in new window or tab >>Liming placed in a long-term perspective: a paleolimnological study of 12 lakes in the Swedish liming program
2007 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 37, no 2, 247-258 p.Article in journal (Refereed) Published
Abstract [en]

Since the 1970s liming has been practised on a large scale in Sweden to mitigate acidification and several thousand lakes and streams are limed repeatedly. The Swedish monitoring program ISELAW (Integrated Studies of the Effects of Liming Acidified Waters) studies the long-term effects of liming. This paper summarizes the paleolimnological part of the program. Sediment cores from 12 lakes were analysed to study the development of the lakes from pre-industrial time until the present, and address questions about natural conditions and the effects of early human impact, acidification, and liming. Diatoms were used to reconstruct the pH history and to study shifts in species composition due to acidification and liming. Analyses of lead and spheroidal carbonaceous particles were applied for indirect dating and as indicators of the atmospheric deposition of pollutants associated with acid rain. Pollen analysis was performed in eight of the lakes to study the vegetation and agricultural history. The natural pH (prior to human disturbance) was between 5.3 and 6.5 in the eight lakes where the complete post-glacial sediment sequence was recovered. Pollen from anthropochores and apophytes indicated early agricultural land use in the vicinity of the lakes from 1000 to 2000 years ago, and pH increased with land use in six of these lakes. Five of the lakes have been acidified during recent decades, and in all 12 lakes some effects of liming were recorded in the diatom assemblage. The lakes show different responses to liming, including a return to a pre-acidification diatom composition or a shift to a state previously not recorded in the lake’s histories. This study accentuates the complexity of biological response to acidification and liming, and highlights the importance of historical perspectives to assess the current state of a lake’s ecosystem and to establish adequate restoration goals.

Identifiers
urn:nbn:se:umu:diva-11880 (URN)doi:10.1007/s10933-006-9014-9 (DOI)
Available from: 2007-03-15 Created: 2007-03-15 Last updated: 2017-12-14Bibliographically approved
2. Monitoring compared with paleolimnology: implications for the definition of reference condition in limed lakes in Sweden.
Open this publication in new window or tab >>Monitoring compared with paleolimnology: implications for the definition of reference condition in limed lakes in Sweden.
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.

Identifiers
urn:nbn:se:umu:diva-11340 (URN)doi:10.1007/s10661-007-0081-9 (DOI)18058250 (PubMedID)
Available from: 2008-12-16 Created: 2008-12-16Bibliographically approved
3. Does liming to mitigate acidification restore the natural diatom community in Swedish lakes? Implications for defining realistic reference conditions.:  
Open this publication in new window or tab >>Does liming to mitigate acidification restore the natural diatom community in Swedish lakes? Implications for defining realistic reference conditions.:  
(English)Manuscript (Other academic)
Keyword
Diatoms, Reference condition, European Council Water Framework Directive, Liming, Acidification, Paleolimnology
National Category
Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-20580 (URN)
Note
Submitted to Journal of Paleolimnology, ISSN 0921-2728 Available from: 2009-03-23 Created: 2009-03-23 Last updated: 2012-01-31
4. Environmental history: A piece in the puzzle for establishing plans for environmental management
Open this publication in new window or tab >>Environmental history: A piece in the puzzle for establishing plans for environmental management
Show others...
2009 (English)In: Journal of Environmental Management, ISSN 0301-4797, E-ISSN 1095-8630, Vol. 90, no 8, 2794-2800 p.Article in journal (Refereed) Published
Abstract [en]

Establishment of plans for environmental planning and management requires that a number of natural and societal factors must be taken into consideration. Insights into the inherent dynamics of nature as well as the role that past human activities have played for establishing the current condition of the landscape and the natural environment in general are essential. Many natural and man-made changes occur over time scales of decades or centuries, and these are difficult to comprehend without a historical perspective. Such a perspective can be obtained using palaeoecological studies, i.e. by geochemical and biological analyses of lake sediment and peat deposits. To illustrate the long-term dynamics of nature and particularly the role of man, we present here five case studies from Sweden concerning pollution, lake acidification, lake eutrophication, biodiversity, and landscape dynamics and conservation – topics of broad interests – and discuss benefits of including a longer time perspective in environmental management.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
pollution, acidification, eutrophication, vegetation change, nature conservation, liming, environmental planning and management, palaeoecology
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-20581 (URN)10.1016/j.jenvman.2009.03.008 (DOI)
Available from: 2009-03-23 Created: 2009-03-23 Last updated: 2017-12-13Bibliographically approved

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