Chemistry Reference
In-Depth Information
to synchronise them with plant uptake remains a major challenge. Farmers
have become increasingly adept at targeting applications of mineral N fertiliser
in arable systems, but using organic fertilisers and ensuring that N is used
efficiently within relatively extensive agricultural systems are key areas of
research for the 21
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century.
3.4 Metals
In the European Union and internationally, a set of research programmes have
focused on assessing the risks of trace metals to ecosystems. This work has
been driven by policy initiatives which include new procedures for the
mandatory risk assessment according to European Commission regulation
1488/94 and studies to support the 1998 Convention on Long-Range
Transboundary Air Pollution Aarhus Protocol on Heavy Metals.
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High
concentrations of metals in the environment are a threat to both soil function
and the delivery of ecosystem services. This is because exposure to sufficiently
high concentrations of trace elements is associated with negative effects on
species, including a range of ecologically important soil taxa.
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Most
problematically, unlike the majority of organic chemicals, trace metals are
not subject to degradation. Instead, once deposited to land, metals can only be
removed by the relatively slow processes of sediment transport and leaching
(and cropping in some systems).
At the national scale, concentrations of trace metals have been relatively well
investigated,
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including previous surveys of trace metal concentrations in soil
across England and Wales.
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Within the GB-based Countryside Survey
project, trace metal concentrations have been measured in soils (0-15cm) from
two surveys conducted in 1998 and 2007 in order provide baseline data on
topsoil trace metal concentrations in support of risk assessment.
Instrumentation developments between surveys, including a transition from
inductively coupled plasma optical emission spectrometry to inductively
coupled plasma mass spectrometry and the adoption of microwave digestion
methods, make direct comparison between surveys difficult. These issues can,
however, be overcome by the comparative analysis of certified reference
materials and individual samples - with these data then used to ''normalise''
differently analysed data-sets.
Comparisons between the two survey data-sets available for the Countryside
Survey project indicated that only small relative changes in soil trace metal
concentrations occurred between surveys. This is despite reported declines in
atmospheric deposition and is presumably due to the long residence time of
metals in soils. Of seven metals for which repeat measurements were made
during the 2007 survey, for only one, Cu, was a statistically significant
difference in soil (0-15cm) concentrations (an increase) found for Great
Britain. When the data for repeat metal measurements were stratified by Broad
Habitat, AVC, and soil organic matter category, further statistically significant
differences were seen. However, because of the need to normalise data-sets
