黄河三角洲互花米草整治对潮滩湿地防灾功效和沉积动力的影响

互花米草作为黄河三角洲外来入侵物种, 2010年开始爆发式蔓延, 2020年面积最大时可超6 000 hm²,对潮间带生物多样性造成了严重影响。自2020年起,黄河三角洲自然保护区开始大规模的互花米草整治与盐地碱蓬生态修复工作。互花米草具有较强的消浪、缓流、促淤、固滩能力,短期内、大范围的植被去除,可能导致波流和沉积动力环境的突变。基于现场观测数据和考虑植被作用的浪、流、沙耦合数值模型,研究分析了互花米草整治和盐地碱蓬修复对黄河三角洲湿地动力过程的影响,重点关注风暴作用下黄河三角洲潮滩湿地的防灾减灾能力和沉积效应变化。研究结果表明,互花米草可有效抵御极端风暴潮,最大风暴潮位衰减率可达15 cm/km。互花米草整治将导致湿地防灾减灾能力显著下降,堤前风暴潮峰值可抬升10～30 cm,同时潮间带的泥沙捕集能力大幅下降。受限于植被密度、高度,盐地碱蓬完全修复后湿地衰减风暴潮、捕集泥沙的能力显著低于原互花米草湿地。研究建议,互花米草整治工程应考虑短期内植被去除导致的近岸风暴潮抬升、侵蚀加剧等潜在风险。

EFFECTS OF SPARTINA ALTERNIFLORA REMOVAL ON STORM SURGE ATTENUATION AND SEDIMENT TRAPPING IN THE INTERTIDAL ZONE OF THE YELLOW RIVER DELTA

Invasive species Spartina alterniflora have dramatically spread in the Yellow River Delta since 2010. The maximum area of S. alterniflora reached 6000 hectares in 2020, exerting a great negative effect on the intertidal biodiversity. Comprehensive regulations have been conducted in the Yellow River Delta National Nature Reserve including S. alterniflora removal and Suaeda salsa restoration since 2020. However, large-scale vegetation removal within a short period caused significant changes in hydrodynamics and morphodynamics of local intertidal wetlands. Therefore, this effect was studied based on field measurements and a process-based model-coupled hydrodynamic and morphodynamic processes, particularly, on storm surge attenuation and sediment trapping capacity. Results show that the maximum storm surge attenuation rate could exceed 15 cm/km when S. alterniflora was present, and the maximum water level would increase by 10~30 cm after vegetation removal. Additionally, S. alterniflora are pivotal to marsh sedimentation, and the regulations could decelerate the sediment trapping efficiency in intertidal flat. On the other hand, limited by stem density and height, local S. salsa are less effective in attenuating storm surges and trapping fine sediments compared to S. alterniflora. This study provides evidence that rapid vegetation removal may put the intertidal zone to a risk of extreme water level height and may stimulate serve erosions. We appeal that integrated assessment and proper strategies should be taken for wetlands natural restoration.