Variability of suspended sediment properties in the saline front of the highly stratified Magdalena River estuary, Colombia

Abstract

Water samples were analyzed with an optical laser device (LISST 200×) to determine the properties of suspended sediments in the saline front of the Magdalena River mouth (Colombia, South America), a micro-tidal delta with high fluvial discharge of regional influence. The study aimed to determine variability of textural properties, suspended sediment concentration, effective density, and settling velocity under non-stationary, stratified, and turbid conditions. The suspended sediment consisted of 84.3% silt-size material (3.9–62.5 μm), with the remaining 15.7% a sand-size fraction (62.5–177 μm). Nevertheless, most of these fractions consisted of flocs, up to 995 μm in size, composed of primary particles that ranged in size from 9 to 35 μm. Most sediments were very poorly sorted, near symmetrical and platykurtic, with mean volumetric suspended sediment concentration, settling velocity, and effective density values of 253.1 μl l⁻¹, 5.8 × 10⁻³ mm s⁻¹, and 0.96 kg m⁻³, respectively. These properties exhibited significant depth-related differences regardless of tidal phase. Data dispersion also increased with depth. Our findings illustrate the influence of stratification on suspended sediment properties, with marked vertical variability over short time scales. Textural properties highlighted different multi-modal features of grain-size distribution. The study also revealed spatial and temporal transitions associated with contrasting sediment transport conditions. Textural analysis enabled comprehensive interpretation of large datasets obtained through laser diffraction measurements.