象山港氮、磷营养盐环流和分布规律的研究

CIRCULATION AND DISTRIBUTION OF NITROGEN AND PHOSPHORUS IN XIANGSHAN BAY,CHINA

采用定点监测分析方法,研究了象山港狭湾内设置的六个固定站位1992—2007年时间段内的硝酸氮(NO3-N)、亚硝酸氮(NO2-N)、铵氮(NH4-N)和磷酸盐(PO4-P)浓度的监测数据,探讨了象山港狭湾内(122°00′E以西)氮、磷营养盐的环流和分布规律。结果表明,(1)除个别年份外,16年内硝酸氮、亚硝酸氮、铵氮和磷酸盐浓度的空间分布,从港顶1号站向港口6号站呈降低趋势,其中以PO4-P、NO2-N的降低趋势最为明显,而NH4-N的降低趋势相对较弱。(2)NO3-N的空间变化规律较为复杂,并且3号站的浓度往往达到最大值。(3)无论是平水期(4月)还是丰水期(7月),表层盐度均低于底层,而表层温度高于底层;盐度从港顶1号站向港口6号站递增,而温度递减。这种分布规律基本上可用余环流模式进行解释,但余环流输运并不是促使营养盐入海的唯一原因,潮振荡的垂向剪切造成的纵向弥散和潮混合亦对营养盐输运有重大贡献。(4)与1992年相比,2007年各站的NO3-N浓度几乎都增加了一倍,PO4-P浓度增幅更大,说明象山港的氮、磷污染与日俱增。

To study the circulation and distribution of nitrogen and phosphorus nutrients in Xiangshan Bay, Zhejiang, China （to the west of 122°00＇E）, concentrations of nitrate nitrogen （NO3-N）, nitrite nitrogen （NO2-N）, ammonium nitrogen （NH4-N） and phosphate （PO4-P） were studied in six stations from 1992 to 2007. Results showed that： （1） The concentrations, especially those of PO4-P and NO2-N, declined overall from Stations 1 to 6 in the 16 years; （2） The distribution of NOa-N was more complicated than others, and often with the maximum at Station 3; （3） Whether in dry （April） or wet season （July）, the salinity at all stations was lower at surface and high at the bottom, and it was warmer at surface than at the bottom. The salinity increased from Stations 1 to 6, while the tendency of temperature was reversed. The distribution could be explained with a residual circulation mode that the nutrients accumulated in the Xihu Bay mostly enter the inner section of the Xiangshan Bay （to the west of No. 1 cross section） with mixing-dispersion by tide-wave action. The nutrients move westward at the bottom layer in residual circulation. At the same time, the accumulated nutrients in the bottom layer of Huangdun Bay, Tie Bay and the northern beach to the west of No. 1 cross section also go into the westward bottom residual circulation. As the residual circulation to the west of No. 1 section features a gravitational nature, its direction at the bottom is westward and at the surface eastward; therefore, nutrients are transported constantly to the surface layer, pass eastward across the No.2 section, and then leave the bay mouth. However, tide-wave action contributes greatly in addition to the residual circulation; （4） The concentrations of NO3-N and PO4-P at all stations in 2007 nearly and more than doubled from those of 1992, respectively, indicating a worsening trend of nitrogen and phosphorus pollution in Xiangshan Bay.