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Most sources of atmospheric dust on Earth are located in the Northern Hemisphere. The lower dust emissions in the Southern Hemisphere in part limit the supply of micronutrients (primarily soluble iron) to the Southern Ocean, thereby constraining its productivity. Climate and land use change can alter the current distribution of dust source regions on Earth. Can new dust sources be activated in the Southern Hemisphere? Here we show that vegetation loss and dune remobilization in the Southern Kalahari can promote dust emissions comparable to those observed from major contemporary dust sources in the Southern African region. Dust generation experiments support the hypothesis that, in the Southern Kalahari, aeolian deposits that are currently mostly stabilized by savanna vegetation are capable of emitting substantial amounts of dust from interdune areas. We show that dust from these areas is relatively rich in soluble iron, an important micronutrient for ocean productivity. Trajectory analyses show that dust from the Kalahari commonly reaches the Southern Ocean and could therefore enhance its productivity.

Research on ecosystem and societal response to global environmental change typically considers the effects of shifts in mean climate conditions. There is, however, some evidence of ongoing changes also in the variance of hydrologic and climate fluctuations. A relatively high interannual variability is a distinctive feature of the hydrologic regime of dryland regions, particularly at the desert margins. Hydrologic variability has an important impact on ecosystem dynamics, food security and societal reliance on ecosystem services in water-limited environments. Here, we investigate some of the current patterns of hydrologic variability in drylands around the world and review the major effects of hydrologic fluctuations on ecosystem resilience, maintenance of biodiversity and food security. We show that random hydrologic fluctuations may enhance the resilience of dryland ecosystems by obliterating bistable deterministic behaviours and threshold-like responses to external drivers. Moreover, by increasing biodiversity and the associated ecosystem redundancy, hydrologic variability can indirectly enhance post-disturbance recovery, i.e. ecosystem resilience.

The exposure of freshwater-dependent coastal ecosystems to saltwater is a present-day impact of climate and land-use changes in many coastal regions, with the potential to harm freshwater and terrestrial biota, alter biogeochemical cycles and reduce agricultural yields. Land-use activities associated with artificial drainage infrastructure (canals, ditches, and drains) could exacerbate saltwater exposure. However, studies assessing the effects of artificial drainage on the vulnerability of coastal landscapes to saltwater exposure are lacking. We examined the extent to which artificial drainage infrastructure has altered the potential for saltwater intrusion in the coastal plain of eastern North Carolina. Regional spatial analyses demonstrate that artificial drainages not only lower the overall elevation in coastal landscapes, but they also alter the routing and concentration of hydrological flows. Together, these factors have the potential to increase the total proportion of the landscape vulnerable to saltwater intrusion, not only in areas adjacent to drainage infrastructure but also in places where no artificial drainages exist due to large scale effects of flow rerouting. Among all land cover types in eastern North Carolina, wetlands are most vulnerable to saltwater exposure. Droughts and coastal storms associated with climate change potentially exacerbate vulnerability to saltwater facilitated by artificial drainage.

[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.

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Many dune fields around the world have undergone alternating periods of mobilization and stabilization in response to changes in wind power and rainfall. However, in modern times disturbances associated with land use are believed to be a dominant factor contributing to the activation of stabilized vegetated dunes in drylands, while the reduction in human activities such as grazing and farming may lead to stabilization of once active dune fields. The Kalahari region of southern Africa has recently begun to exhibit visible signs of dune mobilization, a process that could lead to an activation of aeolian transport in the region with important implications for the biogeochemistry of downwind terrestrial and marine ecosystems. It is still unclear whether the region is poised at a tipping point between its current state (i.e., vegetated fixed linear dunes), and a “degraded” state (i.e., barren and active dunes). Here we investigate the ability of the landscape to recover from the degraded state by assessing the resilience of duneland vegetation and evaluating the vegetation and soil characteristics. Using field observations and soil seed bank experiments, we show that palatable perennial grass cover is reduced while the seedbank is depleted on grazed dunefields. Conversely, the interdunes generally exhibit relatively rich seed banks. Soils from grazed and ungrazed sites show that plant available nutrient contents are not significantly different; therefore, soil nutrients are likely not a major factor limiting the recovery of perennial vegetation in this region. It is observed that the perennial grasses reestablish on the recovering dunes after grazers have been excluded, indicating that the landscape is still able to recover after years of denudation and that any irreversible shift to a stable degraded state is likely during extended periods of disturbance and/or climatic shifts that promote the degraded state. We also find that changes in grass cover, grass community composition, and seed bank can serve as indicators of whether the system has irreversibly shifted from a vegetated to a bare dune state.