Simulating the gross primary production and ecosystem respiration of estuarine ecosystem in North China with AQUATOX

AQUATOX, coupled water quality and estuarine hydrodynamic model based on food web, was implemented to simulate the temporal variations of gross primary production (GPP) and ecosystem respiration (Re) in Haihe estuary of North China, also, the parameter sensitivity was calculated and the main factors of GPP and Re were analyzed. Results showed that GPP ranged from 16 to 1789 mg O2 m−2 d−1 and Re from 56 to 1083 mg O2 m−2 d−1, respectively. GPP and Re exhibited significant temporal variation and both reached the highest level in June, however, GPP and Re reduced in July and August, which could be explained by the increase of turbidity caused by high freshwater inflow discharge in rainy season. Maximum photosynthetic rate of blue-greens was the most sensitive parameter to GPP. Re was strongly related to temperature, the most sensitive parameter was average epilimnetic temperature. A significant negative correlation was found between GPP, Re and freshwater inflow. Furthermore, significant direct and indirect effects of tidal height on GPP were observed by path analysis, increased turbidity induced by tidal action might explain the influence on GPP.