Combined ecohydrological effects of wind regime change and land reclamation on a tidal marsh in semi-enclosed bay

Abstract

Tidal marshes are sensitive and vulnerable to changes in the estuarine circulation. Various anthropogenic and climatic changes challenge the stability and fate of tidal marshes and introduce complicated management problems. Although the wind plays a key role in governing estuarine circulation in bays, few studies have evaluated its ecohydrological effects on tidal marshes and the interactions of its effects with those of anthropogenic activities. In this study, the independent and simultaneous effects of wind regime change and land reclamation projects were evaluated at the Mai Po Tidal Marsh in the Deep Bay, Pearl River Estuary as a case study. In recent decades, the wind regime in the Pearl River Estuary led to a stronger northeast monsoon during the dry season and a stronger southwest monsoon during the wet season. The results of hydrodynamic simulation show that the change in the wind regime and reclamation altered the governing roles of tide and freshwater discharge in the bay’s seasonal estuarine circulation. The reclamation projects in the bay enhanced the effects of the stronger southwest monsoon in accelerating the estuarine circulation during the wet season, but reversed the effects of the stronger northeast monsoon in inhibiting the estuarine circulation during the dry season. Benthic infauna were used as an ecological indicator to assess the stability of the estuarine ecosystem. The predicted spatial averaged biomass of benthic infauna in the tidal marsh increased by 2% annually with the wind regime change but decreased by 28% with the reclamation; these trends were consistent with field observations. Although the change in the wind regime led to a direct reduction in the hydrodynamic disturbance in the tidal marsh and contributed to ecosystem stability, it may have shifted the hydrodynamics from sediment deposition to an erosion environment in the tidal marsh during the dry season, threatening the long-term fate of the tidal marsh.