Growth of Zostera japonica in different sediment habitats of the Yellow River estuary in China.

The estuarine delta of the Yellow River is a region of strong land-ocean-human interactions that undergoes a unique evolutionary process. The delta is formed by deposition of large quantities of sediments carried by the Yellow River, especially during the annual water and sediment regulation period; more than one-third of the total annual sediments is deposited to the estuary area. The seagrass Zostera japonica is located at the forefront of the Yellow River delta. To study the impact of the different sediment environments on the Z. japonica growth, its growth and water quality and sediment parameters were measured on the northern and southern sides of the estuary from April to October in 2019. The action of wind and tides have re-suspended and dispersed sediments over time, producing shores on the southern delta characterized by nutrient-enriched clays and shores on the northern delta characterized by coarser sands and silts with poor nutrients. During the monitoring period, the concentrations of TC, TN, and TP in the root-zone sediments at the southern site were 1.56%, 0.04%, and 0.06%, respectively, whereas they were 0.69%, 0.007%, and 0.06%, respectively, at the northern site. Sufficient nutrients supported the growth of Z. japonica at the southern site, while poor nutrition limited the continuous growth of Z. japonica at the northern site. In July, the plant height, biomass, and shoot density of Z. japonica at the southern site reached the maximum values of 23.6 cm, 0.14 g/shoot, and 3245 shoots/m, respectively, whereas they were 16.4 cm, 0.06 g/shoot, and 2740 shoots/m, respectively, at the northern site. The sediment grain size and their nutrients contributed to different growth patterns of Z. japonica at the southern and northern sites. Our research could provide important implication for the conservation of Z. japonica habitats in the Yellow River estuary in China.