Soil Organic Carbon Baselines for Land Degradation Neutrality: Map Accuracy and Cost Tradeoffs with Respect to Complexity in Otjozondjupa, Namibia

Abstract

Recent estimates show that one third of the world's land and water resources are highly or moderately degraded. Global economic losses from land degradation (LD) are as high as USD $10.6 trillion annually. These trends catalyzed a call for avoiding future LD, reducing ongoing LD, and reversing past LD, which has culminated in the adoption of Sustainable Development Goal (SDG) Target 15.3 which aims to achieve global land degradation neutrality (LDN) by 2030. The political momentum and increased body of scientific literature have led to calls for a 'new science of LDN' and highlighted the practical challenges of implementing LDN. The aim of the present study was to derive LDN soil organic carbon (SOC) stock baseline maps by comparing different digital soil mapping (DSM) methods and sampling densities in a case study (Otjozondjupa, Namibia) and evaluate each approach with respect to complexity, cost, and map accuracy. The mean absolute error (MAE) leveled off after 100 samples were included in the DSM models resulting in a cost tradeoff for additional soil sample collection. If capacity is sufficient, the random forest DSM method out-performed other methods, but the improvement from using this more complex method compared to interpolating the soil sample data by ordinary kriging was minimal. The lessons learned while developing the Otjozondjupa LDN SOC baseline provide valuable insights for others who are responsible for developing LDN baselines elsewhere.The staggering evidence of the magnitude and rate of LD, and its continued negative impacts on food and fiber production and human well-being, catalyzed a call for avoiding future LD, reducing ongoing LD, and reversing past LD. The concept of 'zero net land degradation' (ZNLD) was first mentioned at the UN Convention to Combat Desertification (UNCCD) in 2011 [7].The following year, ZNLD was proposed at the UN Conference on Sustainable Development (Rio+20). Two important events in 2015 further solidified the importance of Land Degradation Neutrality (LDN). The Sustainable Development Goals (SDGs) were adopted by the UN General Assembly and SDG Target 15.3 specifically aims to "combat desertification, restore degraded land and soil, including land affected by desertification, drought and floods, and strive to achieve a land degradation-neutral world" by 2030. Later that year, during the twelfth UNCCD Conference of the Parties (COP), parties decided to integrate LDN into the implementation of the UNCCD.The political momentum (i) translated into new debates, and (ii) increased the body of scientific literature including calls for a 'new science of LDN' [8]. The LDN debates, thus far, have focused on its feasibility [9,10], its scientific conceptual framework [11,12], practical issues concerning operationalization [8,13], and its potential to unify the three Rio Conventions [14]. Meanwhile, the scientific community agreed to connect LDN to the SDG Target 15.3 indicator, which is the 'proportion of land that is degraded over total land area,' and this is measured with t...

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Opportunities and Limitations for Achieving Land Degradation-Neutrality through the Current Land-Use Policy Framework in Kenya

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Mapping soil texture with a gamma-ray spectrometer : comparison between UAV and proximal measurements and traditional sampling : validation study

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