Sediment accumulation rates in European lakes since AD 1850: trends,reference conditions and exceedence |
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| Authors: | Neil L Rose David Morley Peter G Appleby Richard W Battarbee Tiiu Alliksaar Piero Guilizzoni Erik Jeppesen Atte Korhola Jaan-Mati Punning |
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| Institution: | (1) Environmental Change Research Centre, University College London, Gower Street, London, WC1E 6BT, UK;(2) Department of Mathematical Sciences, University of Liverpool, Liverpool, L69 3BX, UK;(3) Institute of Geology, Tallinn University of Technology, Ehitajate Tee 5, 19086 Tallinn, Estonia;(4) CNR-Istituto Per Lo Studio Degli Ecosistemi (ISE), Verbania Pallanza, Italy;(5) National Environmental Research Institute, Department of Freshwater Ecology, University of Aarhus, 8600 Silkeborg, Denmark;(6) Environmental Change Research Unit, Department of Biological and Environmental Sciences, University of Helsinki, Helsinki, Finland;(7) Institute of Ecology, Tallinn University, Uus-Sadama 5, 10120 Tallinn, Estonia |
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| Abstract: | Sediment accumulation rate (SAR) is an important physical parameter in all lakes and increases have been observed in many
over the last c.100 years. This has been ascribed to changes in land-use and land-management causing accelerated catchment
soil erosion and an increase in autochthonous organic matter production. The EU Water Framework Directive requires that assessment
of biological, hydromorphological and chemical elements of water quality should be based on the degree to which present day
conditions deviate from those expected in the absence of significant anthropogenic influence, termed reference conditions.
Currently however, the reference condition for sediment accumulation rate for lakes of different types is undefined. To improve
our understanding of the controls on SARs we compiled SAR and lake typology data for 207 European lakes derived from 210Pb dated cores to assess how rates have changed through time (in 25 year classes) both overall and for lakes of different
types. Seventy-one percent of these sediment cores showed surface SARs higher than “basal” (mainly nineteenth century) rates,
11% showed no change while 18% showed a decline. Lakes were then classified into lake-types using four variables: alkalinity
(3 classes), altitude (3 classes), maximum depth (2 classes) and lake area (2 classes). This generated a possible 36 lake
classes of which 25 were represented in the dataset. Nine lake-types contained >10 lakes. Little change in SAR occurred prior
to 1900 and most increases occurred in more recent periods, in particular 1950–1975 and post-1975. This indicates a general
acceleration in SAR in European lakes during the second half of the twentieth century. Reference SARs were estimated for six
lake-types with the highest number of sites. European mountain lakes had the lowest reference SAR (0.005 ± 0.003 g cm−2 yr−1) while lowland, high alkalinity sites had the highest (0.03–0.04 g cm−2 yr−1). SARs for other lake-types ranged between 0.012 and 0.024 g cm−2 yr−1. Using the mountain lake-type as an example, the 1850 reference SAR appears to show good agreement with available data for
lakes beyond Europe indicating these values may be more broadly applicable. Contemporary SARs in lakes of all classes showed
exceedence over their defined reference SAR. This may be partly due to diagenetic processes. Greatest exceedences were found
in shallow, low altitude lakes and these are considered to be the ones under the greatest threat from continued elevation
of SAR. It is considered that climate change may play a progressively more important role in driving SAR in the future. |
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