Ancient manuring practices pollute arable soils at the St Kilda World Heritage Site, Scottish North Atlantic Andrew A. Meharg a, * , Clare Deacon a , Kevin J. Edwards b , Margaret Donaldson c , Donald A. Davidson d , Christian Spring d , Charles M. Scrimgeour e , Jo ¨ rg Feldmann f , A. Rabb f a Department of Plant and Soil Science, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK b Department of Geography and Environment and Northern Studies Centre, University of Aberdeen, Elphinstone Road, Aberdeen AB24 3UF, UK c School of Geography and Geosciences, University of St Andrews, St Andrews KY16 9AL, UK d School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK e Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK f Department of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Aberdeen AB24 3UE, UK Received 18 August 2005; received in revised form 30 January 2006; accepted 30 January 2006 Abstract The impact of ancient fertilization practices on the biogeochemistry of arable soils on the remote Scottish island of Hirta, St Kilda was investigated. The island was relatively unusual in that the inhabitants exploited seabird colonies for food, enabling high population den- sities to be sustained on a limited, and naturally poor, soil resource. A few other Scottish islands, the Faeroes and some Icelandic Islands, had similar cultural dependence on seabirds. Fertilization with human and animal waste streams (mainly peat ash and bird carcases) on Hirta over millennia has led to over-deepened, nutrient-rich soils (plaggen). This project set out to examine if this high rate of fertilization had adversely impacted the soil, and if so, to determine which waste streams were responsible. Arable soils were considerably elevated in Pb and Zn compared to non-arable soils. Using Pb isotope signatures and analysis of the waste streams, it was determined that this pol- lution came from peat and turf ash (Pb and Zn) and from bird carcases (Zn). This was also confirmed by 13 C and 15 N analysis of the profiles which showed that soil organic matter was highly enriched in marine-derived C and N compared to non-arable soils. The pol- lution of such a remote island may be typical of other ‘bird culture’ islands, and peat ash contamination of marginal arable soils at high latitudes may be widespread in terms of geographical area, but less intense at specific locations due to lower population densities than on Hirta. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: As; Cu; Pb; Zn; Peat ash; Plaggen soils; Seabirds 1. Introduction Isolated island communities of the North Atlantic Ocean contend with poor soil resources, low temperatures and high precipitation (Amorosi et al., 1998). Colonization of these islands depends upon alternative protein sources to substitute for unavailable or inadequate vegetables and grain production, or agricultural soils have to be improved with locally devised manures (Simpson, 1997; Davidson and Carter, 1998; Simpson et al., 1999). Fishing is an obvi- ous food source, but seabirds can also be procured (Bald- win, 1974) as, for instance, in the Westmanns, Iceland, the Faroe Islands, and the Scottish islands of Mingulay, North Rona and Hirta (Fig. 1). Perhaps the most famed of these ‘bird culture’ islands is Hirta in the St Kilda archi- pelago (Harman, 1997), which has been occupied since at least the Iron Age and arguably much longer (Fleming 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.01.076 * Corresponding author. Tel.: +44 1224 272264; fax: +44 1224 272703. E-mail address: a.meharg@abdn.ac.uk (A.A. Meharg). www.elsevier.com/locate/chemosphere Chemosphere xxx (2006) xxx–xxx ARTICLE IN PRESS