Establishing natural sediment reference conditions for metals and the legacy of long-range and local pollution on lakes in Europe |
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| Authors: | Richard Bindler Johan Rydberg Ingemar Renberg |
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| Institution: | 1.Department of Ecology and Environmental Science,Ume? University,Ume?,Sweden |
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| Abstract: | The intention of the European Water Framework Directive (WFD) and the national guidelines that implement the WFD is that present-day
conditions and future management strategies are to be based on an understanding of reference conditions for the particular
water body of interest. In the context of non-synthetic pollutants such as lead, mercury and cadmium, the criteria for a high
ecological status are that “concentrations are] within the range normally associated with undisturbed conditions”. How this
normal range is to be defined is open to interpretation; for example, in Sweden reference conditions based on sediment records
are defined as the conditions prior to modern industrialization, i.e. prior to the mid-1800’s. These pre-industrial reference
conditions would correspond to sediments 15–30 cm depth. However, ‘reference conditions’ are not always synonymous with ‘natural
background conditions’. Analyses of long sediment profiles from Swedish lakes and from a few other areas, however, have shown
that pre-industrial pollution—at least with regard to lead—was extensive. Atmospheric lead pollution has its origin in antiquity,
with a small, well-defined peak already during the Greek-Roman period 2,000 years ago. Sediments deposited 300–500 years in
Sweden and Scotland, for example, show a dominance of pollution lead, and in some sediment records also cadmium and copper
pollution was extensive. Thus, in order to characterize natural background concentrations of metals, long sediment profiles
are needed to reach sediments unaffected by pollution (>3,000 years BP); this can correspond to sediments below 50 cm in some
lakes, but in others sediments below 300 cm or more. |
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