What is the primary source of sediment in coastal regions?

The primary source of sediment in coastal regions is erosion from land, river runoff, and ocean wave action because these processes contribute significantly to the transport and deposition of sediments along coastlines.

Erosion occurs as rain, wind, and other natural forces break down rocks and soil on land, which are then carried into the ocean by rivers and streams. The sediment from these sources is critical in shaping coastal landscapes and contributes to beach formation and the dynamics of coastal ecosystems. Additionally, ocean waves continuously erode coastal cliffs and shorelines, further adding to the sediment supply deposited along the coast.

Other aspects such as biological decay and marine organisms do play a role in sediment formation, particularly in creating organic sediments like shells or corals. However, these contributions are secondary to the extensive sediment generated by terrestrial processes and water action. Ocean currents also influence sediment distribution and transportation but are not a primary source of sediment in coastal regions. Thus, the comprehensive impact of land erosion, river runoff, and wave action solidifies the choice as the most accurate representation of sediment sources in these environments.