Mangroves are particularly effective at trapping sediments with their extensive root systems, and other plants that live in mangrove swamps, for example the Jellybean plant, help in this process. This is a small succulent shrub related to the cactus, which has many tiny roots which help trap many of the finer sediments and prevent them from being washed away. Assimilate Wastes Sewage and storm water wastes contain nitrates and phosphates from fertilizers and detergents, heavy metals from industrial plants, in addition to all the other nasties that waste water contains. These waters are often pumped straight into rivers or the ocean, with little treatment. Mangroves and estuaries are the last places these wastes pass through before reaching the ocean, and are an important sink for a large proportion of the waste.
Mangroves absorb a a large amount of the nutrients.
Chemical processes that occur when fresh and salt water meet bind heavy metals to fine sediments, where they fall out of the water column and remain until released again by disturbance. Human activities such as dredging and clearing of vegetation 'reactivates' these waste products and allows them to continue to the ocean where they may damage coral reefs, sea grasses and other marine habitats. Natural processes can also reactivate the waste, but this occurs over a much longer time scale. Freshwater is quite scarce in comparison. The absorption assists in flood mitigation, by controlling the outflow of water.