Biogeochemical processes and eutrophication status of nutrients in the northern Beibu Gulf, South China

Sources of nitrate in a heavily nitrogen pollution bay in Beibu Gulf, as identified using stable isotopes

“…In addition to being affected by industrial activities, Xi Bay is also affected by a large amount of terrestrial contaminant input from the Fangcheng River in the upper bay (Lao et al, 2020). It is reported that a higher contaminant level was found in the coastal bay, including high nutrient loads, particularly in the rainy seasons (Lao et al, 2019b;Lao et al, 2021a). This is mainly affected by the heavy land-source discharge during the rainy seasons (Lao et al, 2021a).…”

“…Beibu Gulf is a semi-enclosed gulf and a newly developing industry and port area in the northwestern South China Sea (SCS). There are several rivers around the northern Beibu Gulf, and the influence of runoff input by the rivers and tidal influx from the outer gulf constitutes a well estuary-bay multi-ecosystem and has become an important mariculture area in China (Lao et al, 2020 andLiu et al, 2020;Xu et al, 2020: Xu et al, 2021Lao et al, 2021a;Lao et al, 2022a and2022b). However, with the rapid development of local urbanization and industrialization, the coastal bays in Beibu Gulf have been subjected to a high loading of contaminants from anthropogenic inputs, such as domestic, industrial, port and agricultural waste (Lao et al, 2019b;Xu et al, 2020: Lao et al, 2021aLao et al, 2021b;Lao et al, 2021c;Lao et al, 2021d: Xu et al, 2021and Lao et al, 2022a.…”

“…There are several rivers around the northern Beibu Gulf, and the influence of runoff input by the rivers and tidal influx from the outer gulf constitutes a well estuary-bay multi-ecosystem and has become an important mariculture area in China (Lao et al, 2020 andLiu et al, 2020;Xu et al, 2020: Xu et al, 2021Lao et al, 2021a;Lao et al, 2022a and2022b). However, with the rapid development of local urbanization and industrialization, the coastal bays in Beibu Gulf have been subjected to a high loading of contaminants from anthropogenic inputs, such as domestic, industrial, port and agricultural waste (Lao et al, 2019b;Xu et al, 2020: Lao et al, 2021aLao et al, 2021b;Lao et al, 2021c;Lao et al, 2021d: Xu et al, 2021and Lao et al, 2022a. The nutrients discharged into coastal bays from runoff input have increased over the past 20 years, and the increase in phosphorus input has decreased the N/P ratios in several coastal bays in the Beibu Gulf (Lao et al, 2020 andLao et al, 2021c).…”

“…The nutrients discharged into coastal bays from runoff input have increased over the past 20 years, and the increase in phosphorus input has decreased the N/P ratios in several coastal bays in the Beibu Gulf (Lao et al, 2020 andLao et al, 2021c). Moreover, the eutrophication of some coastal bays in the Beibu Gulf has increased in recent decades due to the increase in terrestrial nutrient input, particularly the nitrogen input (Lai et al, 2014;Guo et al, 2020;Lao et al, 2021a andLao et al, 2021c;Pan et al, 2021). In addition, sewage is the dominant nitrate source in most bays/areas in the Beibu Gulf, which is identified by the dual nitrate isotopes (Pan et al, 2021;Lao et al, 2021b;Chen et al, 2022).…”

“…It is reported that a higher contaminant level was found in the coastal bay, including high nutrient loads, particularly in the rainy seasons (Lao et al, 2019b;Lao et al, 2021a). This is mainly affected by the heavy land-source discharge during the rainy seasons (Lao et al, 2021a). However, in such bays that are seriously affected by intensive human activities (i.e., industrial and port activities), the sources of nitrate are poorly understood.…”