Monitoring compared with paleolimnology: implications for the definition of reference condition in limed lakes in Sweden

Abstract

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.

Environmental history: A piece in the puzzle for establishing plans for environmental management

“…In Sweden the surface-water liming program to mitigate the effects of acid rain is extensive; since 1976 it has included 8000 lakes and 12,000 km of watercourses and the costs for the period 1983-2007 have been >300 million Euro (Naturvårdsverket, 2007). However, critics have argued that not only lakes acidified by acid rain, but also that, in some cases, naturally acidic lakes have been limed (Bishop et al, 2001), and palaeolimnological investigations confirm that this is the case (Guhré n et al, 2007;Norberg et al, 2008). As an example, Fig.…”

The Role of Palaeolimnology in Implementing the Water Framework Directive in Ireland

“…Palaeolimnology has enabled validation of the critical loads model through the reconstruction of acidifi cation histories (Smol et al 1998). More recently, monitoring records were compared with palaeolimnological reconstructions in limed lakes in Sweden (Norberg et al 2008), and results indicate that some lakes had never acidifi ed in the fi rst place, suggesting the need to set realistic mitigation goals.…”

Palaeolimnological assessment of the reference conditions and ecological status of lakes in Estonia - implications for the European Union Water Framework Directive

“…Therefore we applied diatom-based reconstruction for defining reference conditions in Estonian lakes. Diatoms have been used for establishment of background baseline conditions for lakes in many EU states like Great Britain (Bennion et al 2004), Ireland (Leira et al 2006), Denmark (Bjerring et al 2008), Sweden (Norberg et al 2008), and Finland (Räsänen et al 2006).…”