Effects of tidal hydrology on soil phosphorus forms in the Yellow River estuary wetland: A field study of soil core translocation

Phosphorus (P) forms in soil are related to the P cycle and play an important role in maintaining the productivity and function of wetlands. Tidal hydrology is a key factor controlling soil P forms in estuary wetlands; however, the response of soil P forms to tidal hydrological changes remains unclear. A translocation experiment in the Yellow River Estuary wetland was conducted to study the effect of hydrological changes on P forms in the soil, in which freshwater marsh soils in the supratidal zone were translocated to salt marshes in different intertidal zones (up-high-tidal zone, high-tidal zone, and middle-tidal zone). Over a 23-month experiment, soil properties showed varying changes under different tidal hydrology conditions, with an increase in pH, salinity, Ca2+ and salt ions and a decrease in iron oxide and nutrients. Compared with the control, the content of different forms of phosphorus (total phosphorus, inorganic phosphorus, organic phosphorus, and calcium-bound phosphorus) in the cultured soil cores decreased from 3.3 % to 67.0 % in the intertidal zones, whereas the content of ferrum‑aluminum-bound phosphorus increased from 58.9 % to 65.1 % at the end of the experiment. According to the partial least squares structural equation model, P forms are influenced by tidal hydrology mainly through the mediation of salt ions and nutrient levels. These results suggest that seawater intrusion promotes the release of P in the supratidal zone soil of estuary wetlands.