Soil seed bank and vegetation differences following channel diversion in the Yellow River Delta.

Vegetation plays a key role in influencing the morphodynamics of river deltas, yet channelization of most of the world's rivers limits delta movement and resulting vegetation patterns. Thus, our understanding of vegetation dynamics in newly formed and abandoned deltaic wetlands is still poor. The artificial channel diversion of the mouth of the Yellow River in 1996 created conditions that mimic a natural delta lobe shift by increasing freshwater, sediment, and nutrient supply to wetlands along the new Yellow River course (NYR) and allowing seawater encroachment in the abandoned Yellow River course (OYR). To examine the effects of this river channel shift on the vegetation and seed bank structure, above-ground vegetation and seed bank species richness and diversity were examined from the channel to the marsh interior in wetlands of both OYR and NYR. A total of 17 plant species were found growing across both sites, 9 species were in OYR and 16 species in NYR. Soil depth did not influence seed bank density in OYR, but the seed bank density in the 0-5 cm soil layer was significantly greater than in the 5-10 cm soil layer in NYR. Species diversity of the vegetation and soil seed bank was strongly influenced by soil salinity and hydrology, which varied along the gradient from seaside to river bank. There was a greater separation in species composition between seed bank and vegetation in the OYR than in the NYR. The findings suggest that channel diversion of the Yellow River Had a significant effect to the above-ground vegetation. However, the species richness and diversity of soil seed banks in the OYR was similar to that of the NYR, indicating that seed banks had a greater tolerance to external disturbance compared with vegetation.