北部湾入海河流营养盐的分布特征及入海通量研究

于2018年2月(枯水期)和8月(丰水期)对南流江、大风江、钦江、茅岭江和防城江等北部湾主要的入海河流开展调查，分析这些河流各形态营养盐的浓度特征及入海通量。结果表明，不同时期营养盐浓度差异较为明显，主要表现为枯水期防城江、茅岭江和钦江的营养盐浓度较丰水期高，而丰水期大风江和南流江的营养盐浓度高于枯水期，表明丰水期大风江和南流江污染较为严重。丰水期，${rm {NO}}_3^- $是溶解态无机氮的主要成分，但枯水期防城江和大风江${rm {NH}}_4^+ $比例升高。根据径流量资料和河流营养盐浓度，估算出2018年北部湾入海河流的氮和磷的入海通量分别为1014607 t和47929 t，其中溶解态无机氮占总氮的77%，${rm {PO}}_4^{3-} $占总磷的40%。丰水期，南流江营养盐入海通量总体较高，其次是大风江，防城江、茅岭江和钦江的营养盐入海通量相对较小。枯水期，受区域污染影响，不同河流营养盐的入海通量变化较大。与历史对比，北部湾河流的营养盐入海通量显著升高，表明河流营养盐输入的升高可能是北部湾近海水体富营养化加重的重要因素。北部湾河流不同时期氮和磷输入量的差异，可能会对北部湾近岸及邻近海域生态系统产生较大影响。

Distribution characteristics and fluxes of nutrients in the rivers of the Beibu Gulf

Observations were carried out at Nanliu River, Dafeng River, Qinjiang River, Maoling River and Fangcheng River in the Beibu Gulf to analyze the distribution characteristics and fluxes of nutrient in February (dry season) and August (flood season) 2018. The results showed that significantly variations of nutrient concentration were observed, and the nutrient concentrations in the Fangcheng River, Maoling River and Qinjiang River in the dry season were higher than that in the flood season, while the nutrient concentrations in the Dafeng River and Nanliu River in the flood season were higher than that in the dry season. Nitrate (${rm {NO}}_3^- $) was the predominant species of dissolved inorganic nitrogen (DIN) during the flood season, while the ${rm {NH}}_4^+ $ content in the Fangcheng River and Dafeng River increased during the dry season. Based on the runoff data and nutrient concentration, the fluxes of nitrogen and phosphorus into the Beibu Gulf were calculated to be 1014607 tons and 47929 tons respectively in 2018, of which DIN accounted for 77% of total nitrogen and ${rm {PO}}_4^{3-} $ accounted for 40% of total phosphorus. During the flood river, higher nutrient fluxes were found in the Nanliu River, followed by Dafeng River, Fangcheng River, Maoling River and Qinjiang River. While in the dry season, the flux of nutrients from rivers to the coastal gulf changed significantly due to the influence of regional pollution. Compared with the historical data, the fluxes of nutrient into the coastal gulf increased significantly, which may be responsible for the increase of water eutrophication in the coastal Beibu Gulf. High and different terrestrial inputs transported by the rivers in northern Beibu Gulf may lead to an extensive impact on the ecological system of the Beibu Gulf.