Documenting soil redistribution on livestock-poached pasture using caesium-134 and cobalt-60 as tracers

Greenwood, P.; Meusburger, K.

Land Degradation and Development 30(3): 315-327


ISSN/ISBN: 1085-3278
DOI: 10.1002/ldr.3226
Accession: 070902461

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Poaching is caused by the excessive trampling of soil and vegetation by herd animals and is prevalent in intensively managed grasslands. It is viewed as detrimental to soil fertility, has the potential to contribute to soil erosion, and thus represents a form of land degradation that is unsustainable. Attempts to document sediment redistribution by poaching have been hampered by a lack of techniques capable of measuring the movement of poached material at requisite spatial and temporal scales. We present a new tracing technique, using caesium-134 (Cs-134) and cobalt-60 (Co-60), which is designed to overcome those problems. Nine areas (plots) of grassland, each measuring 0.04 m(2), were directly labelled with a known activity of either Cs-134 or Co-60. Three plots were located on level, unpoached ground for use as controls, and six were located in livestock-poached areas. Initial surface inventories were documented and then remeasured on three occasions after rainfall. Inventory changes were converted to estimates of sediment redistribution, which was documented across all poached plots at each remeasurement. Erosion represented the predominant mechanism, with average soil losses estimated at an equivalent of 0.03 kg m(-2) d(-1) at the first remeasurement (T1), 0.11 kg m(-2) d(-1) at T2, and 0.18 kg m(-2) d(-1) at T3. Despite assuming erosion would diminish, increasing soil loss is attributed to reduced surface roughness. These findings not only confirm the viability of the tracing technique but also demonstrate that livestock-poached areas act as sediment sources over timescales of at least a few months after poaching has ceased.