Tidally driven porewater exchange and the key affecting factors in mangroves in the Pearl River Estuary, China

Mangroves are important ecosystems that mediate the movement of organic matter and nutrients from land to the ocean via tidally driven porewater exchange. In the present study, we quantified porewater exchange rates in three 12-year-old Sonneratia apetala plantations distributed along the Pearl River Estuary in southern China by monitoring 222 Rn in situ during the wet and dry seasons and by measuring the correlations between the porewater exchange rates and the mangrove plantation conditions. The 222 Rn-derived porewater exchange rates were 385.1–1286.0 Bq m −2 h −1 in the wet season and 380.6–498.4 Bq m −2 h −1 in the dry season, which is higher than previous studies. Therefore, it is necessary to sample and monitor within the mangrove forests, or the porewater exchange should be underestimated because of the ignored richer crab burrows. Sediment pH, salinity, and surface water pH had significant relationships with the porewater exchange rate. These results revealed that porewater exchange had seasonal and spatial variation in mangroves and that pH and salinity were the major regulators of mangrove porewater physical exchange. • The richer crab burrows in the mangrove sediments enhance the vertical mixing of porewater and surface water in mangroves. • Porewater exchange had seasonal and spatial variation in mangroves. • pH and salinity are the major regulators of mangrove porewater physical exchange. • Sampling and monitoring in the mangrove forests is necessary, or the porewater exchange rates will be overestimated.