Sedimentary organic-13C revealed dispersal patterns of Spartina alterniflora intra- and inter-estuary in China

Patterns of long-distance spread of invasive plants via wind and water have been proposed and simulated. Spartina alterniflora can be seen anywhere along the Chinese coastline but its naturally spreading patterns remain unclear. Given the linearity between δ13C abundance in sediment and colonizing time of S. alterniflora, a C4 plant, we used organic δ13C abundance in surface sediment from the well-developed patches to understand its spread pattern in seven invaded estuaries along the Fujian coastline, including two intentionally introduced estuaries. δ13C abundance (‰) in sediments from the seven invaded estuaries were −21.2 ± 0.8, −20.3 ± 0.5, −20.7 ± 1.0, −23.5 ± 0.4, −22.4 ± 0.5, −23.2 ± 0.7, and −22.1 ± 0.9, respectively, from north to south. Luoyuan and Feiluan estuaries with the intentional plantings had significantly greater δ13C abundances than other invaded estuaries. Significant correlations of δ13C abundance with electric conductivity (positive) and particle size (negative) (p < 0.01, n = 113) in sediments from the seven estuaries indicate the invasion success sequence of S. alterniflora. Taiwan Straits' northward alongshore surface current, switching to southward in winter, might play a crucial role in dispersing seeds of S. alterniflora among estuaries along the Fujian coast. In comparison with the two intentionally planted estuaries, Yacheng estuary showed a clear δ13C pattern that declined from seaside to inner estuary. It suggests that a natural invasion at intra-estuary scale with seeds transported by the alongshore surface currents from the two intentional planted estuaries or the upper province. Variations of δ13C abundance among the naturally invaded estuaries suggest that other factors might regulate niche availability for S. alterniflora invasion success, such as discharges and sediment topographic features. Moreover, a linear relationship was discovered between δ13C and δ15N abundances in invaded sediments, suggesting that microbially mediated nitrogen removal processes might prevail and result in 15N enrichment due to habitat modification by S. alterniflora invasion.