Geoscience Reference
In-Depth Information
Directive (WFD) aims to achieve 'good ecological quality, that is, little deviation relative to an
undisturbed baseline/reference condition. A similar measure of biological integrity is used in
the US Clean Water Act (Gell 2010, Battarbee and Bennion 2011). Databases and modelling
also present opportunities for simulating the effects of local management interventions
within the context of regional drivers of water availability, and the effects of global drivers like
nitrogen deposition, changes in phosphorus cycling, and climate change (Battarbee and
Bennion 2011, Battarbee et al. 2012).
Soil management, carbon storage, and sustainable agriculture
in the tropics
Food security is an urgent priority as environmental concerns burgeon alongside the growing
human population, the tendency to focus on increasingly industrialized agriculture and the
associated impacts on biodiversity. There is therefore renewed interest in agricultural tech-
niques that allowed civilizations to persist sustainably for millennia without degrading their
environment. Such techniques are variously described as traditional management, trad-
itional indigenous knowledge and biocultural diversity (Cocks 2006), but regardless of termi-
nology, they show the ability to respond and adapt to variable environments, and the proof of
their success is in their longevity (Berkes et al. 2000). One of the most fascinating examples
comes from the anthropogenic dark earths, found in tropical forests of the Amazon and cen-
tral Africa, where skilled management has supported the provisioning of ecosystem services
like soil formation, food production, and carbon storage, potentially providing a model for
sustainable agriculture and contributing to biodiversity conservation in some of the world's
hottest biodiversity hotspots (Glaser 2007, Glaser et al. 2001).
Despite their lush appearance, tropical rainforests grow on very poor soils, which have low
organic matter content and low fertility. This is because the warm, moist conditions of the
tropics are ideal for microbial growth, and as a result organic matter in soils breaks down very
rapidly. Most carbon in the system is locked up in living plant material and is unavailable for
new plant growth. In order to grow crops, people usually cut vegetation and then burn it on
site, releasing nutrients for food crops, which can only be sustained for a few years before the
soil becomes depleted and the land is abandoned. This practice of slash and burn agriculture
is unsustainable, because new areas of forest must be regularly cleared. In the Amazon,
population growth and more intensive clearance because of logging and cattle ranching has
put further stress on soils and biodiversity in recent decades (Glaser and Birk 2012).
Though sensitive to current, destructive slash and burn agriculture, tropical forests have
been inhabited for millennia and have fostered agricultural techniques that hold promising
lessons for the future. Small areas of dark earth or terra preta (black earth) have been found
scattered throughout the Amazon basin, mainly in the vicinity of major rivers (Figure 6.5a).
Most terra preta patches are about 20 ha in size, but in total they cover more than 50,000 ha in
Central Amazonia and possibly as much as 10% of the whole of Amazonia (Glaser 2007, Gla-
ser and Birk 2012). Dark earths have much higher and more stable organic matter content
 
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