三沙湾水质分布特征对陆源污染、湾内养殖的响应

根据福建三沙湾海域2018年洪季一个定点站和12个走航站的5项营养盐及水文资料，研究发现:（1）三沙湾沿岸城市排放水是主要的污染源。其中，蕉城区外大金溪湾的硝酸盐、氨盐、悬沙含量、硅酸盐和磷酸盐浓度，在落潮盐度最小时期（宁德城区排放水）分别是涨潮盐度最大时期（海水）水质浓度的1.2倍、3.6倍、6倍、2.5倍和2倍。（2）三沙湾营养盐从陆向海的变化既受陆域河流排放的影响，也受湾内养殖排放的影响。其中NO₃-N和SiO₃-Si浓度受陆源排放影响较大，从陆向海分别下降了31%和50%。而NO₂-N、NH₄-N和PO₄-P浓度变化受湾内养殖的影响，从陆向海下降的趋势不明显。（3）12个走航站无机氮（DIN）的平均值为57.33 μmol/L，大于21.41 μmol/L；PO₄-P平均值为2.28 μmol/L，大于1.45 μmol/L；DIN/DIP基本为8~30。这些参数表明三沙湾水质已经超四类海水水质标准，并达到富营养化状态。

Responses of distribution of water quality in the Sansha bay on the land discharge and aquaculture

Based on nutrients and hydrological data of one fixed station and twelve navigation stations in 2018 flood season in the Sansha bay, Fujian province, this paper found: (1) The average concentrations of SiO₃-Si、NO₃-N、NH₄-N、PO₄-P and SSC in ebb (includes drainage of the Ningde city) are about 1.2, 3.6, 6, 2.5 and 2 times higher than that in the flood (seawater) in Dajinxi estuary, respectively. (2)The concentrations of NO₃-N and SiO₃-Si decrease by 31% and 50% with the increased of salinity, the result indicated SiO₃-Si and NO₃-N variation were controlled by river discharge. However, with increase of salinity, the concentrations of NH₄-N and PO₄-P showed a slight decrease trend, and NO₂-N even showed an increase trend, the result implicated that change of NH₄-N、PO₄-P and NO₂-N were mainly controlled by aquaculture in the bay. (3) The average concentrations of inorganic nitrogen (DIN) on twelve navigation stations was 57.33>21.41 μmol/L, PO₄-P (DIP) was 2.28>1.45 μmol/L, and DIN/DIP was between 8～30, such level of above parameters indicated that the water quality in the Sansha bay had exceeded the grade IV water quality standard and reached the state of eutrophication.