Purification evaluation of DIN and DIP in different types of wetlands in Jiaozhou bay and Daya bay

In order to evaluate the purification capacities of DIN and DIP in different types of wetlands in two typical semi-closed bays (Jiaozhou bay and Daya bay) in China, a quantitative method of seawater-groundwater exchange was used to calculate the purification capacities. Results showed that: there are four wetland types in Jiaozhou bay, including sandy beaches, mud flats, estuarine intertidal zones and tidal marshes, and their purification capacities on DIN sort as follows: mud flats>sandy beaches>estuarine intertidal zones> tidal marshes and DIP sort as follows: sandy beaches>mud flats>estuarine intertidal zones> tidal marshes. The purification rate ranged from 2.11×10⁵ mol/d to 4.23×10⁵ mol/d for DIN and from 4.29×10² mol/d to 8.22×10² mol/d for DIP, respectively. The estimated nitrogen removal rate due to human activities such as land reclamation decreased by 3.1～5.4 t/d. In contrast, there are three wetland types such as mangrove swamps, sandy beaches and silt-sandy beaches in Daya bay. The DIN purification capacities in different types of wetlands in Daya bay sort as follows: mangrove swamps>sandy beaches>silt-sandy beaches, with an average of 4.22×10⁷ mol/d. Due to the area decrease of mangrove swamps and sandy wetlands in Daya bay, the decreased nitrogen removal rate was estimated to be 1.33×10² t/d and 0.81 t/d, respectively.