Tidal dynamics amplify the potential of biochar incorporation for sediment carbon sequestration in estuarine wetlands: evidence from in-situ experiments

Abstract

Estuarine wetlands serve as essential carbon sinks; however, their sequestration capacity is increasingly threatened by anthropogenic activities and climate change. While biochar incorporation shows promise for restoration, its role and mechanism in estuarine wetlands remain poorly understood. Most research has focused on terrestrial ecosystems without considering the unique conditions of estuaries, including strong hydrodynamics and persistent sediment deposition. To bridge this gap, we conducted a 1-year in-situ experiment in the Chongming Dongtan wetland to assess the carbon sequestration potential of reed straw-derived biochar under tidal influence. Compared to the control and straw return treatment, biochar incorporation significantly suppressed sediment respiration by 49.01% and 61.53% (p < 0.05), respectively. Consequently, biochar achieved an average 31.37% increase in soil organic carbon content relative to the control, outperforming its application in comparable agricultural ecosystems. Furthermore, biochar significantly decreased the ratios of dissolved and easily oxidizable organic carbon (p < 0.05), indicating improved soil organic carbon stability. Mechanistically, tidal dynamics and sediment deposition altered the impact of biochar on sediment properties, specifically by decreasing NH₄⁺-N, maintaining bulk density, and increasing sand/clay ratio, which were identified as key factors affecting microbial activity by redundancy analysis and structural equation modeling. These shifts inhibited microbial carbon mineralization by reducing functional genes (e.g., chiA, FAEB, and pel) and associated genera (Anaeromyxobacter and Geobacter), while enriching genes and microbial taxa related to carbon stabilization, such as aspB and Anaerolinea. Thus, the carbon sequestration potential of biochar in estuarine wetlands was amplified. These findings offer valuable insights into biochar incorporation in wetland restoration and enrich our understanding of its role across diverse ecosystems, suggesting that it may yield greater carbon benefits in estuaries than in terrestrial ecosystems.

Graphical Abstract

Keywords

Biochar / Estuarine wetland / Tidal stress / Carbon sequestration

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Funding

National Natural Science Foundation of China(52170115)

Science and Technology Commission of Shanghai Municipality(21DZ1201802)

Natural Science Foundation of Xinjiang Uygur Autonomous Region(2025D01C314)

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The Author(s)