In aquatic environments, what primarily drives sediment transport?

• A. Wind
• B. Gravity and movement of water
• C. Tectonic uplift
• D. Thermal expansion

Answer: (B)

Sediment transport in aquatic environments is driven by the movement of water itself, which comes from gravity pulling water downhill and creating currents. When water flows, it exerts shear stress on the bed; if this stress exceeds the particles’ threshold, grains are picked up and moved. Depending on flow strength and particle size, sediment travels as bedload along the bottom or remains suspended in the water column, with turbulence helping keep finer particles aloft and carrying them farther. Wind can shape surface conditions by generating waves, but the primary mechanism for transporting most sediment in rivers, lakes, and oceans is the gravity-induced movement of water and the resulting currents. Tectonic uplift influences the supply and landscape, not the ongoing transport momentum, and thermal expansion has negligible impact on moving sediments.