Impacts of river inputs and aquaculture on nutrient dynamics in Qinglan Bay and adjacent coastal waters in East Hainan, China

Nitrogen and phosphorus are vital nutrients for maintaining aquatic ecosystem health, with estuaries serving as critical conduits for nutrient transport into the ocean. Understanding the spatial distribution and dynamics of nutrients in estuaries is essential for assessing their ecological impact and informing water quality management. We investigated the spatial distribution and forms of dissolved inorganic nitrogen and phosphorus in Qinglan Bay, East Hainan, China, focusing on the impacts of riverine inputs and intensive aquaculture activities. Results indicated elevated nutrient concentrations near river sources, diminishing towards the ocean. Aquaculture operations contribute notably to nitrogen and phosphorus levels, primarily introducing ammonium and dissolved organic phosphorus. Despite these inputs, Qinglan Bay exhibits a strong capacity for nutrient self-purification through biological uptake and sedimentation, thereby mitigating the potential ecological burden on adjacent coastal environments. Moreover, the outflow from the bay with low DIN/DIP ratio may impact the biogeochemistry of neighbouring coastal waters.