Final answer:
Dammed streams that supply sediment to longshore transport can result in increased coastal erosion, changes in silt loads impacting river ecology, and physical alterations of riverine systems both upstream and downstream.
Step-by-step explanation:
If all of the streams supplying sediment to longshore transport are dammed, a significant disruption of the natural flow of sediment along the coastline would occur. Sediment transport is crucial to maintaining the shape and health of shorelines, delivering materials that build beaches and form protective barriers. Without the continual supply of sediment, coastline erosion could accelerate, leading to the loss of coastal habitats. Furthermore, the buildup of a reservoir behind the dams alters the natural silt loads of the rivers, affecting their ecology and resulting in significant physical changes both upstream and downstream.
Dammed rivers often show a reduction in sediment flow, which means deltas and beaches downstream would not receive new material to offset erosion. This can lead to increased beach erosion and potentially alter the natural landscapes, affecting local ecosystems and human infrastructure. Additionally, changes in water temperature, chemistry, flow characteristics due to the dams can lead to a significant impact on the aquatic habitats and fisheries, especially for species relying on sediment-rich waters for spawning and growth.