Suspended sediment transport in the Mariuá archipelago: A megacomplex anabranching system in the Negro River (Amazon Basin)

Abstract This study investigates the interactions between sediments and biota in the Mariuá Archipelago, a mega‐complex anabranching reach of the Negro River, the main blackwater river in the Amazon Basin, to understand the dynamics of the ecosystem in cratonic systems with limited supply. Using satellite imagery and hydrological data (2019–2024), we characterized suspended sediment concentration (SSC) patterns and evaluated geomorphological controls on habitat stability. Results revealed minimal inter‐channel SSC variation (6.53–7.32 mg.L −1 ) across the archipelago, contrasting sharply with sediment‐rich Andean tributaries. Annual suspended sediment flux decreased 23% through the archipelago (4.48 × 10 6 ton.year −1 upstream to 3.38 × 10 6 ton.year −1 downstream), indicating net retention of 1.10 × 10 6 ton.year −1 within inter‐island lakes and floodplains. The low specific sediment yield (12–15 ton.km −2 .year −1 ) and the contemporary sedimentation rate (0.10 ± 0.05 mm.year −1 ) contrast with Middle Holocene formation conditions, when the Negro River had higher energy and a greater sediment concentration than at present. Low correlations between SSC, water discharge and precipitation (r ≤ 0.51) demonstrate limited environmental forcing in this cratonic landscape. Spatial analysis reveals that downstream lakes function as suspended sediment sinks, concentrating fine particles during low‐water periods and supporting distinct aquatic plant communities. This supply‐limited regime enables ecosystem stability through reduced sediment‐mediated disturbance, maintaining persistent habitats for endemic biota since the Pleistocene. However, mining, deforestation and climate change threaten this equilibrium by potentially increasing suspended sediment inputs beyond historical ranges. Geomorphological constraints in ancient cratonic systems promote long‐term ecological stability, rather than disturbance‐driven dynamics. This study provides new insights for the conservation planning of fluvial ecosystems in this unique landscape.