2.2.5.7. Lateral Fluxes of Carbon
In addition to vertical fluxes (to the atmosphere), there are a number of lateral
fluxes of carbon and plant nutrients at the land surface or in the soil interior.
A human-induced activity that leads to degradation in one location may result
in aggradation elsewhere (e.g., nutrient transfers).
Examples at the biome/agro-ecosystem/agro-ecological zone level follow:
- Extraction and off-site distribution of products or organic materials derived
from ecosystems (see Section 2.4.2.2).
- Large-scale biomass burning (natural vegetation or crop residues) and wind
erosion can result in soot and dust being carried off-site by the wind. Transported
materials include volatized soil organic matter, carbon-soot particulates
and nitrogen compounds in subhumid areas, or calcium- and phosphorus-enriched
particulates from desert areas (e.g., Nadelhoffer et al., 1999).
- Human-induced water erosion in upper catchments of watersheds may result
in downriver formation of new land with enriched nutrients and organic matter
content.
- Within the soil profile itself, there can be slow but continuous percolation,
and subsequent lateral transport through groundwater flows, of dissolved organic
matter (DOM). An example is the catchment of the Rio Negro in the Amazon region.
Its waters are acid and deep-brown colored, containing many fulvic acids ("rios-de-agua-preta;"
Sioli, 1984). These DOMs may end up in sedimentary deposits when they come
in contact with silt-loaded river waters ("rios-de agua-branca"), or at the
riverine sedimentation front in seas and oceans (Richey et al., 1980; Meybeck,
1982).
Examples of lateral carbon fluxes at the landscape level follow:
- Water erosion may result in accumulation of debris down-slope, as colluvia
at the mouth of drainage ways, or as alluvia of the local river system. The
particulate organic matter so displaced may become buried deep in the sedimentary
layers of these deposits, effectively immobilizing the entrenched organic
carbon matter, unless the new lands become incorporated in the local agricultural
tillage system (see Section 1.4.1).
- Before the use of chemical fertilizers in Europe and Asia, there often was
deliberate displacement of organic matter and nutrient-rich topsoil from forests
and heathlands to the arable fields around villages, directly or through a
cattle-stable or "night-soil" phase. This practice is still prevalent in many
rural communities in sub-Saharan Africa (FAO, 1995a; Smaling, 1998) and elsewhere.
In contrast, much of the organic effluent of industrialized countries is transported
out of the terrestrial biosphere into aquatic systems.
If human activities that induce changes in soil organic matter are included
as Protocol activities under Article 3.4, these lateral transfers (since 1990)
will need to be taken into account, guided by a careful analysis of the local
land-use system.
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