Spatial and temporal changes of phosphorus in coastal wetland soils as affected by a tidal creek in the Yellow River Estuary, China

•Significant differences were observed in soil TP between June and other months.•No significant differences in soil TP and AP among different sampling sites.•Soil P supply was generally lower with lower AP:TP ratios less than 2%.•TP was significantly correlated with BD, Al, Mg, C:P ratios and soil moisture.•AP was just significantly correlated with soil organic matter.

In order to investigate spatial and temporal changes of soil phosphorus and its availability in coastal wetlands in the Yellow River Estuary, soil samples from five sampling sites (Sites 1–5) in four sampling periods were collected and the contents of soil phosphorus and other properties were detected. Our results showed that there were no significant differences in total phosphorus (TP) in surface and subsurface soils among the five sampling sites (p > 0.05), whereas significant differences were observed between June and other months (p < 0.05) following the order June > August > November > April. Generally, available phosphorus (AP) contents also showed a fluctuation in different sampling periods and there were significant differences between November and August and April at 10–20 cm soil layer (p < 0.05). The soil P supply was generally lower with lower AP:TP ratios less than 2%. Spatial changes along the sampling belt in AP:TP ratios were similar in surface soils except for April, whereas they decreased in subsurface soils in June and November, and fluctuated slightly in August and April. Lower C:P ratios (<50) in coastal wetland soils contributed to soil P mineralization. Spatial changes in the C:P ratios were similar the surface soils in four sampling periods, and the reverse changing tendencies were observed in subsurface soils between April and June and between August and November. Correlation analysis showed that TP had significant positive correlations with Al, Mg and bulk density and negative correlations with soil moisture and C:P ratio (p < 0.01). Comparatively, AP was just significantly correlated with soil organic matter. The findings indicated that seasonal changes in soil P should be given more concerns to minimize the eutrophication risk of water bodies in coastal wetlands and guide the flow and sediment regulation regime of the upstream reservoir.