Potential risks of climate change and tropical storms on ecosystem and clams culture activities in Giao Thuy, Nam Dinh, Vietnam

Abstract Ecosystem and aquaculture in estuary areas are sensitive to climate change and severe climatic events. In this study, three environmental monitoring events were carried out on a 1800-ha clam culture area in Giao Thuy district, Nam Dinh province, Vietnam. The first monitoring was carried out in fair weather. The second and 3rd monitorings were conducted two days after the Ma On and Noru storms, respectively. The variation of water and sediment physicochemical variables, zoobenthos and plankton composition and density, and clam pathogen were investigated at five locations. In addition, long-term variations of temperature, rainfall, and sunshine duration in the area were investigated. The results illustrated the increased temperature, rainfall, and sunshine duration tendency. The clam-cultured species and activities had substantially changed. Ma On and Noru negatively impacted water quality by decreasing the water quality index by 39% and 30%, respectively. Storms decreased water salinity, alkalinity, and sediment’s phosphorus, iron, lead. However, they increased water’s nitrite, phosphorus, total suspended solid, phytoplankton, zooplankton density, and sediment’s total nitrogen, cadimium. The total Vibrio spp. density in clam highly fluctuated between the two storm events. The effect of storm varied according to site location. Shallow and domestic wastewater adjacent sites suffered high risks of extreme temperature, salinity variation, and organic pollution.