Soil carbon storage and retention: a critical synthesis on concepts, research opportunities and sustainable application in environmental engineering

Soil functions have been threatened by anthropogenic activities, compromising ecosystem services and unbalancing the carbon biogeochemical cycle. Soil carbon sequestration (SCS) is an emergent solution for mitigating climate change and restoring degraded soils. Soil organic carbon (SOC) stock plays a relevant role in measuring ecosystem restoration projects. Nevertheless, the soil is complex and heterogeneous. It is subjected to the soil-plant-atmosphere system interaction and is controlled by many multidisciplinary processes in the C cycle, from C air sequestration to C soil retention. There are still a series of uncertainties around concepts, mechanisms and methodological protocols to assess SOC stock. Through a critical literature review, this paper aimed to synthesize concepts with a cross-disciplinary approach, to analyze research opportunities and to examine sustainable applications in light of environmental engineering. The results point out the conceptual advances in organic matter stabilization in soil and highlight the research gap on the dynamics of the SOC and soil water flux within structured soil profiles, which may be explained using geotechnical engineering concepts. We also observed the need for a multidisciplinary framework of variables that is able to clarify the transdisciplinary contributions to this field. Finally, the SOC stock is an index that may be employed as an indicator of ecosystem restoration results in C-based engineering solutions.