Drainage Efficiency and Geometric Nuances of Tidal Channel Network Mediate Spartina alterniflora Landward Invasion in Marsh-Channel System

• Published in: Frontiers in Marine Science Vol. 9
• Main Authors: Zheng, Shaoyan, Shao, Dongdong, Gao, Weilun, Nardin, William, Ning, Zhonghua, Liu, Zezheng, Cui, Baoshan, Sun, Tao
• Format: Journal Article
• Language: English
• Published: Frontiers Media S.A 02-06-2022
• Subjects: drainage efficiency; geometric features; remote sensing; Spartina alterniflora; tidal channel network; vegetation dynamic model
• ISSN: 2296-7745; 2296-7745
• DOI: 10.3389/fmars.2022.888597

As an aggressive invasive salt marsh plant,
Spartina alterniflora
has been found to invade along tidal channel networks and threaten native salt marsh ecosystems. Previous studies have established patterning correlations between
S. alterniflora
invasion and tidal channel functions (drainage efficiency). However, a systematic analysis of
S. alterniflora
invasion in relation to functional and geometric features of tidal channel networks is still lacking. In this study, we extracted tidal channel networks from remote sensing images of the Yellow River Delta, China, and performed numerical experiments to examine
S. alterniflora
invasion patterns with tidal channel networks with varying drainage efficiency and geometric nuances. An existing vegetation dynamics model was adapted to incorporate hydrochorous seed dispersal and salinity buffer zone as the primary mechanisms of tidal channels to facilitate vegetation colonization and was further coupled with Delft3D. We analyzed the correlation of the simulated
S. alterniflora
area with a comprehensive set of tidal channel functional and geometric metrics across different spatial scales. Our results confirmed that watersheds with higher drainage efficiency (larger tidal channel density (
TCD
) and geometric efficiency (
GE
), smaller overmarsh path length (
OPL
)) attained larger
S. alterniflora
area. Given a similar drainage efficiency, tidal channel networks with greater geometric mean bifurcation ratio enhanced
S. alterniflora
invasion. On a local scale, channel order dictated local drainage efficiency (spatially-varying
TCD
o
) and further influenced
S. alterniflora
area. The observed patterns were further verified in principle by two real cases in the Yellow River Delta. Finally, in viewing the efficacy of all metrics tested and further considering their computational costs, we proposed a holistic metric framework consisting of global metrics including
TCD
and geometric mean bifurcation ratio and local metric including spatially-varying
TCD
o
, to assess how tidal channel network mediates
S. alterniflora
invasion in particular and salt marsh vegetation expansion in general in marsh-channel systems.