Potential dust emissions from the southern Kalahari's dunelands

Abstract

[1] The Southern Hemisphere shows relatively low levels of atmospheric dust concentrations. Dust concentrations could, however, increase as a result of losses of vegetation cover in the southern Kalahari. There is some evidence of an ongoing remobilization of stabilized dunefields in the southern Kalahari where dune crests with sparse vegetation cover are reactivated during dry and windy periods, a phenomenon that is predicted to intensify with increased land degradation, overgrazing, and droughts. Despite the potentially important climatic and biogeochemical implications of dust emissions from the Kalahari, it is still unclear whether the predicted remobilization of the Kalahari dunes could be associated with increased dust emissions from this region. The dependence of sediment fluxes and dust emissions on vegetation cover in the Kalahari dunelands remains poorly understood, which prevents a quantitative assessment of possible changes in aeolian activity in this region under different land use and land cover scenarios. In this study, we report the results of an aeolian sediment sampling campaign over a variety of land covers in the southern Kalahari. We use these results to quantify the potential rate of dust emissions and its dependence on vegetation cover and to make an estimate of dust fluxes from a portion of the southern Kalahari. The results show that the loss of vegetation could lead to substantial increases in dust emission and nutrient loss.

Biogeochemistry of dust sources in Southern Africa

“…Although the iron in the fine fraction appears to be not enriched, atmospheric processing that leads to increase in bioavailability of iron could play an important role in determining if iron in dust from Southern Africa will have major impacts on ocean productivity. A recent study shows that the potential dust flux from the southern Kalahari due to devegetation is about 0.42 Tg yr À1 (e.g., Bhattachan et al, 2013), which may not be a substantial contribution in the global context however, an increased delivery of soluble iron, TN and TP in dust from the southern Kalahari to the Southern Ocean could have significant impacts on ocean productivity. The iron enrichment ratio values for pan sediments (both at the Etosha and Makgadikgadi pans) are variable; with larger enrichment ratio found in sediments sampled from the surface of the pan.…”

“…Recent studies have assessed the potential of the southern Kalahari to become an important dust source in the Southern Hemisphere (e.g., Bhattachan et al, 2012Bhattachan et al, , 2013 and dust from these dunefields will commonly reach the Southern Ocean (Bhattachan et al, 2012). The remobilization of stabilized dunes in the southern Kalahari can result in dust emissions comparable to the currently active Makgadikgadi and Etosha pans (Bhattachan et al, 2012).…”

Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the Southern Ocean?

“…The percentage of clay and silt sized particles is greater in the Mallee sediments than in the southern Kalahari interdunes (for southern Kalahari grain size data see Bhattachan et al16). However, we note that the percentage of clay and silt sized particles in soil is not a robust measure of dust generating potential of a source and other mechanisms such as sandblasting, and breaking up of loose aggregates during erosion could affect the dust generating potential43.…”

“…Land-use practices such as deforestation and overgrazing have potential to activate new dust sources in the Southern Hemisphere1415 with significant impacts to downwind soils and ecosystems. Potential new dust sources that could be activated as an effect of land use have been identified in Patagonia14, the Kalahari16, while in Australia the effect of land use on dust emissions has seldom been investigated in the context of its impact on ocean productivity.…”

Resilience and recovery potential of duneland vegetation in the southern Kalahari

“…In the southern Kalahari, dune mobilization occurs during dry and windy periods when vegetation cover decreases below ;14% (Wiggs et al 1995), though a dramatic increase in aeolian transport is observed already when vegetation v www.esajournals.org cover is less than 40% (e.g., Bhattachan et al 2013). Indeed, bare, mobile dunes are ubiquitous in the southern Kalahari and are usually found closer to villages on communal lands and overgrazed farms.…”