Beaver dams are remarkable engineering feats that profoundly alter freshwater ecosystems. When beavers construct dams using tree branches, stones, and mud, they block the natural flow of streams. Consequently, the water pools upstream, creating expansive wetlands and ponds. This sudden accumulation of standing water slows down the stream's current, allowing suspended sediment to settle to the bottom rather than being carried downstream. Over time, the trapped sediment builds up rich, nutrient-dense soil layers that encourage the growth of diverse aquatic vegetation. Furthermore, the slow-moving water in these ponds seeps into the surrounding ground, which directly raises the local water table and keeps nearby soil moist even during dry summer months. Although some landowners complain that beaver activity floods low-lying roads, ecologists emphasize that these wetlands act as natural sponges, reducing the severity of downstream flooding during heavy storms.
According to the passage, the settling of suspended sediment to the bottom of beaver ponds is directly caused by which of the following?
- Athe gradual accumulation of nutrient-dense soil layers
- the slowing down of the stream's currentAnswer
- Cthe seepage of slow-moving water into the surrounding ground
- Dthe flooding of low-lying roads near the beaver dams