Chemistry Reference
In-Depth Information
agriculture and plantation forestry. Vegetation has a fundamental impact on
soil formation and behaviour. Meta-analysis of afforestation research,
principally in temperate latitudes, showed that the extensive planting of forest
monocultures has been associated with depletion of soil Ca
2+
,K
+
and Mg
2+
,
increase in Na
+
, and a mean pH decrease of 0.3. In addition, soil C and N were
observed to decrease, though principally under pine.
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Conversely, recent
research from the tropics has indicated that in very acid tropical soils, planting
with pine may actually increase soil pH.
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A further change observed with
forestry, especially pine plantations, is the development of soil water
repellency, both through afforestation and exacerbation by forest fire.
57
d
n
1
r
2
n
g
|
1
Soil
water
repellency
can
alter
soil
hydrological
behaviour
and
enhance
soil
erosion.
Biosphere change indirectly affects soil biota and the processes that they
drive, by altering plant community composition, nutrient cycling, carbon
allocation patterns, or the quantity and quality of plant-derived organic
materials.
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Many of these processes, and linkages between above and below
ground, are not well understood. Many researchers suggest a high degree of
functional equivalence in the soil decomposer community, and hence
substantial redundancy in species richness and diversity, which makes it
difficult to assess the impacts of global change on soil biota.
Pollution of the biosphere, for instance by heavy metals, can cause harm to
soil ecosystems. A number of keystone soil taxa, e.g. earthworms, springtails,
and nitrifying bacteria, are particularly sensitive to metals. High heavy-metal
concentration in soils can reduce the abundance and diversity of communities
of these and other taxa, potentially resulting in a breakdown of specific soil
functions such as decomposition, nutrient turnover and the regulation of
hydrological flows through soil and the resulting delivery of ecosystem
services. Metals are not broken down over time (unlike most organic
chemicals) and so can be removed only by the relatively slow process of
cropping and leaching. The accumulation of metals presents one of the more
serious long-term threats to soil sustainability worldwide.
2.3 Mapping Global Soil Change
The development of soil mapping stems largely from the need to identify and
value land for the production of food, feed and fibre. This has resulted in
inventories of soils and maps of their spatial distribution, often based on soil
development characteristics such as soil horizons. With regard to the
ecosystems approach, there is much more of a need to understand how soils
are changing, which is not easily determined from the classical soil inventories
and maps. The need to understand how soils change has led to attempts to
resurvey soils, such as that for England and Wales for soil C content.
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Moreover, dedicated monitoring frameworks have been designed to detect soil
change, the longest running of which is the Countryside Survey for Great
Britain,
25
which has monitored ecosystems and soil stocks since 1978. Similar
