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

Abstract

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 ²²²Rn in situ during the wet and dry seasons and by measuring the correlations between the porewater exchange rates and the mangrove plantation conditions. The ²²²Rn-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.