A three-dimensional coupling evaluation model for carbon source-sink in riparian zones

Abstract

Riparian zones, with high carbon sequestration capacity, play a critical role in watershed carbon cycles. Current riparian carbon sink assessments primarily focus on drawdown zones or only consider riparian ecological process, neglecting hydrological process. The objective of this study is to develop a three-dimensional coupling evaluation model for riparian carbon source-sink integrating ecological and hydrological processes, which include vertical, lateral, and longitudinal dimensions. (i) Vertical carbon source-sink: carbon release via respiration and carbon sequestration via photosynthesis. (ii) Lateral carbon source-sink: carbon loss via slope runoff erosion and carbon interception through soil conservation. (iii) Longitudinal carbon source-sink: carbon depletion by riverbank scouring of runoff and carbon sequestration by fluvial sediment deposition. Applied to the Fuhe River, the results show that: (i) The riparian zone of Fuhe River is a net carbon sink (593.0 t·a^-1), with an economic value of 25,410.1 CNY. Vertical carbon process is a net carbon sink (5,657.0 t·a^-1), while the lateral and longitudinal processes act as net carbon source (2,607.0 and 2,457.0 t·a^-1, respectively). (ii) By riparian zone sections, the water-level fluctuation zone acts as a net carbon source (3,680.3 t·a^-1), while the riverbank zone functions as a net carbon sink (4,273.3 t·a^-1). (iii) Spatially, the upstream and midstream are net carbon sinks (513.04 and 234.35 t·a^-1, respectively), while the downstream is a net carbon source (154.41 t·a^-1). (iv) Enhancing vegetation coverage to boost photosynthetic capacity is key to increase carbon sink, and strengthening soil conservation measures to cut organic carbon loss from soil erosion is crucial for reducing carbon source.