doi:10.1016/j.chemosphere.2006.01.076
Copyright © 2006 Elsevier Ltd All rights reserved.
Ancient manuring practices pollute arable soils at the St Kilda World Heritage Site, Scottish North Atlantic
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Andrew A. Meharga, , , Clare Deacona, Kevin J. Edwardsb, Margaret Donaldsonc, Donald A. Davidsond, Christian Springd, Charles M. Scrimgeoure, Jörg Feldmannf and A. Rabbf
aDepartment of Plant and Soil Science, University of Aberdeen, Cruickshank Building, St Machar Drive, Aberdeen AB24 3UU, UK
bDepartment of Geography and Environment and Northern Studies Centre, University of Aberdeen, Elphinstone Road, Aberdeen AB24 3UF, UK
cSchool of Geography and Geosciences, University of St Andrews, St Andrews KY16 9AL, UK
dSchool of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK
eScottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK
fDepartment of Chemistry, University of Aberdeen, Meston Building, Meston Walk, Aberdeen AB24 3UE, UK
Received 18 August 2005;
revised 30 January 2006;
accepted 30 January 2006.
Available online 20 March 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 densities 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 pollution came from peat and turf ash (Pb and Zn) and from bird carcases (Zn). This was also confirmed by 13C and 15N 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 pollution 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.
Keywords: As; Cu; Pb; Zn; Peat ash; Plaggen soils; Seabirds
Fig. 1. Locations mentioned in the text: (A) the eastern north Atlantic; (B) the Outer Hebrides; (C) sample sites on Hirta.
Fig. 2. Pb and Zn levels (open circles) and Pb 206/207 ratios (solid line) in soil and peat profiles. The Peat core was 14C-dated (uncalibrated dates shown on the right-hand Y axis).
Fig. 3. P, C (12C solid line, DPB dotted line) and N (14N solid line, δN dotted line).
Fig. 4. Selected palynological data from the Conachair core. Pollen taxa are percentages of TLP. The 14C dates (uncalibrated) were used for dendrochronological correction to calendar years (see text for details).
Fig. 5. The effect of ashing (at 350 °C in a muffle furnace for 24 h) on Pb and Zn concentrations in soil from Hirta. Diagonal hatch, peat; cross hatch, ultra basic; horizontal hatch, basic and no hatch, granite underlying geologies. The ratio graph is ash/soil concentration, the circle is the weight of soil/weight of ash. Samples were collected from non-arable areas on the island (N = 3, bars are ±standard error).
Fig. 6. Examples of elemental distributions from a thin section sample collected from 15 to 23 cm from the base of the consumption dyke (site 8). In the centre of each image is a bone fragment approximately 1.7 mm in length. Note that the elemental measures are on a relative scale. The bone fragment is obvious in the Ca map where it shows up red. (For interpretation of colour in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Pb and Zn concentrations in bird femurs excavated from an excavated ash floor from an 1850s black house (solid bars), compared to modern samples collected on Hirta. N = 5 for all archeological samples, n = 6 for modern puffin and 2 for modern fulmar. Bars are ±standard error.
Fig. 8. Pb and Zn levels from the island of South Uist on a representative croft garden soil pit (●) and neighbouring non-agricultural land 5 m from the garden (○). Three pits were dug per site, spaced at 1 m distance, with the central location being the centre of the garden. The data points represent the mean of these three sites ± standard error. The garden shown is the representative of 14 garden plots sampled from South Uist.
Table 1.
Isotopic characterization of fresh bird femurs from Hirta sampled in 2002
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