Targeting critical zones: A review of heterogeneity identification methods and driving mechanisms of watershed phosphorus transport

Abstract

Non-point source phosphorus (P) transport is characterized by pronounced heterogeneity manifested in spatial clustering, temporal intermittency, and structural coupling, which together pose critical challenges for watershed management. Based on a systematic synthesis of existing studies, this review proposes a three-dimensional identification framework of hotspots-hot moments-critical source areas (H-M-C) and refines it into the concept of high-risk heterogeneous core units to characterize functional units that are co-activated by multidimensional conditions at the event scale and dominate phosphorus flux outputs. Methodologically, we trace the evolution of approaches from threshold-based criteria, distributed modeling, stable isotopes and geochemical fingerprinting, to intelligent data-driven methods, highlighting their complementarities and limitations in dimensional coverage, mechanistic interpretation, and cross-scale applicability. Furthermore, we summarize the “activation-amplification-regulation-feedback” mechanism chain from four perspectives: hydrological disturbances, land-use practices, geomorphic regulation, and multi-source feedbacks. This review emphasizes the necessity of perceiving non-stationary processes, developing scale-adaptive identification granularity, and constructing strategy-oriented feedback loops, thereby providing a structural framework and methodological pathways to bridge the gap between mechanistic understanding of phosphorus transport and practical management responses.