Enhancing dune sand with biochar: mechanisms, evidence, risks, and a research programme for desert and coastal systems

Abstract

Biochar amendments are increasingly proposed to “enhance dune sand” by increasing water retention, nutrient availability, microbial colonisation, and vegetation establishment, thereby stabilising mobile sands and improving resilience in arid and coastal landscapes. Yet dune sands are not merely “sandy soils”; they are active geomorphic substrates governed by aeolian transport thresholds, sediment supply, surface moisture, fetch effects, and vegetation–sediment feedbacks. We synthesise evidence spanning soil physics, soil microbiology, dune eco-geomorphology, and governance, and critically evaluate the applicability of biochar for dune systems. Meta-analyses indicate that biochar often increases plant-available water in coarse-textured soils by roughly one-quarter on average, with stronger effects at moderate-to-high application rates and depending on biochar properties and placement. Mechanistic studies show that biochar alters pore networks and can increase the abundance and diversity of microbial communities, with larger pores (>5 μm) and heterogeneous pore architectures linked to the provision of microbial habitats and community shifts. Dune-specific risks include particulate emissions and loss of biochar carbon via wind-driven abrasion and resuspension, with laboratory and field evidence that biochar amendments can substantially increase PM emissions under certain wind regimes. We propose an integrated research programme combining (i) microcosm studies isolating pore-structure and inoculation effects; (ii) mesocosm and wind-tunnel experiments quantifying erosion resistance, threshold shear velocity, and particle loss; (iii) field trials in desert and coastal dunes with coupled hydrological and geomorphic monitoring; and (iv) modelling that links pore-scale processes to dune-scale evolution metrics. We also assess regulatory and standards landscapes, including EU fertilising product rules for pyrolysis/gasification materials, biochar certification thresholds for PAHs/heavy metals, and carbon market durability requirements.