Hydrodynamic and wind-driven influences on suspended sediment concentration in estuaries of the Southern Gulf of St. Lawrence

Estuaries play a vital role in coastal ecosystems, serving as nurseries for marine life, natural filters for water quality, and critical zones for sediment trapping. The Southern Gulf of St. Lawrence (Canada), characterized by diverse hydrodynamic and meteorological conditions, hosts estuaries essential to the region’s ecological health and economic sustainability. Suspended sediment concentration (SSC), often approximated by turbidity, is a key indicator and a determinant of estuarine condition, influenced by freshwater discharge, water speed and direction, water level, and meteorological factors. This study investigated tidal phase-specific SSC dynamics and quantified SSC–environment linkages across five Canadian estuaries: two in New Brunswick (Bouctouche and Cocagne) and three in Prince Edward Island (Dunk, Morell and West) using Canonical Correlation Analysis (CCA) applied separately to flood and ebb tides. Freshwater discharge and water velocity were the dominant drivers across all systems, with effects depending on tidal phase, water velocity measured by an ADCP deployed in each estuary exerted stronger control during flood in Bouctouche, West, and Morell, while freshwater discharge influence peaked during ebb in Dunk and Cocagne. Hydrodynamic and meteorological variables explained 16–67% of SSC variance. Wind effects were generally secondary, but more influential in longer fetch systems such as Bouctouche and Cocagne. Inter-estuarine comparisons revealed distinct sediment regimes: tidal-fluvial coupling in West and Morell, mixed tidal-wind interactions in Dunk and stronger wind-associated SSC variability in Bouctouche and Cocagne. These results demonstrate that SSC responses are not uniform but reflect shared physical drivers filtered through site-specific geometry and exposure, and they provide a quantitative basis for estuary-specific sediment management in the Southern Gulf of St. Lawrence. • Near-bed SSC variability is jointly controlled by discharge, tidal currents, and wind forcing. • Tidal phase modulates which drivers dominate SSC variability across estuaries. • Wind forcing enhances SSC in estuaries with longer fetch, consistent with resuspension. • Site-specific geometry filters common forcings into distinct SSC response regimes.