Recent environmental change and human impact on Svalbard: the lake-sediment geochemical record *

As part of a broader investigation into recent environmental change on Svalbard, the inorganic geochemical record of six lake-sediment cores was analysed. The major temporal trends in sediment elemental composition are driven by variations in two contrasting sediment components, both derived from catchment soils: (1) mineral matter, and (2) soil organic matter (SOM), enriched in Fe and Mn oxides and heavy metals. Two environmental impacts are recorded in most or all of the lake sediment sequences. An up-core increase in organic matter can be partly attributed to diagenetic effects, but also requires an enhanced supply of SOM relative to mineral matter. In addition, the central and southern sites all show a ca. 1970 event characterised by an enhanced mineral matter accumulation rate. This requires either an enhanced allochthonous supply or an enhanced mobilisation of littoral sediments. In either case a regional-scale driving force, such as a shift in climate, is required. At five of the lakes the sediment heavy metal concentration profiles can be explained entirely by natural factors. However, at Tenndammen (U), situated close to the Svalbard’s largest settlement at Longyearbyen, possible anthropogenic Pb enrichment is found. Comparison of observed and expected heavy metal profiles (based on Greenland ice-core data) shows that the lakes are generally too insensitive to have recorded a long-transported heavy metal pollution signal. Introduction Growing concern about the state of Arctic environments, still amongst the most pristine in the world, has generated a need to establish base-lines for ecosystem disturbance. The establishment of such base-lines is not, however, straightforward. In Svalbard, for example, the relatively long history of coal mining (since the late nineteenth century) makes it necessary to consider the state of the environment not just at present, but also prior to recent human activities (Rose et al. 2004). With the continuing potential for fossil fuel exploitation on Svalbard (Holte et al. 1996), the establishment of base-line data for Svalbard is doubly important. One of the principal concerns is the impact of long-transported atmospheric pollution, and possible contamination of Arctic ecosystems. Rose et al. (2004) show that significant amounts of spheroidal carbonaceous particles (SCPs) and anthropogenic organic pollutants are present in the sediment of the studied lakes. However, the picture for heavy metal pollution is made more complex by the importance of natural sources. The natural fluxes of heavy metals to lakes are controlled by biogeochemical cycling in the catchment, which is subject to alteration by both natural change and human disturbance. To understand the lake sediment record of heavy metal fluxes, it is therefore necessary to understand temporal changes in the catchment. It is known that heavy metal fluxes to the Arctic have increased in modern times: there are marked increases in heavy metal concentration and accumulation rates in glacial ice (Boutron et al. 1995; Hong et al. 1996) since the Industrial Revolution. However, such increases are small, and it is not certain that a measurable impact will be seen in lake ecosystems. In a comparison between recent and pre-industrial lake sediments in Svalbard, Rognerud et al. (1998) found that only Hg was significantly enriched above natural sediment