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长江流域内工农业生产发达,人口密集,社会发展繁荣,是我国重要的经济区域之一[1]. 作为我国第一大河,长江的多年平均径流量高达9300余亿m3,占据我国入海径流总流量的51%以上[2]. 巨量的长江冲淡水携带巨量的营养物质输入长江口及东海,对河口及邻近海域的水文、地貌、生物等产生重要而深远的影响[2-3].
长期以来,许多学者对长江口及其邻近海域营养盐分布规律进行了研究. 例如,刘春兰等[1]对长江口附近海域的营养盐含量调查显示,其溶解无机氮、活性磷及硅的平均浓度分别为0.62、0.030、1.21 mg·L−1. 王文亮等[4]、张锦辉等[5]分析探讨了长江口及邻近海域内磷酸盐的形态特征和影响因素,刘雅丽等[6]描述了长江口邻近海域内营养盐的季节变化,王文涛等[7]利用同位素手段研究探讨了短周期氮循环过程及特征,丰富了对河口区氮循环和迁移转化的认知. 陈慧敏等[8]报道称,长江口邻近海域氮、磷的浓度呈增加趋势,在20世纪90年代以来增长显著,其溶解无机氮及活性磷酸盐浓度范围在0.027—1.34及0.0007—0.043 mg·L−1.
另一方面,长江冲淡水入海后扩展范围极广,沿水流扩散形成不同的区域,如舟山附近海域内由长江口咸淡水混合形成的羽状锋区域[9-10],各区域有其独特的理化特征. 舟山邻近海域形成我国四大渔场之一,也是长江口鳗苗、杭州湾鲳鱼等多种经济鱼类产卵场及幼鱼索饵场[11]. 本文对2020年夏季8月份长江口邻近海域的营养盐进行分析,探讨该区域内营养盐的分布特征及可能的影响因素,为进一步研究该海域营养盐的输送、转化和迁移等过程提供基础资料.
2020年夏季长江口邻近海域的营养盐含量及分布特征
Nutrients content and distribution characteristics of the Yangtze River Estuary in summer, 2020
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摘要: 本研究根据2020年夏季SOPHI航次21个站位水体中6项营养盐(NH4+-N、NO2−-N、NO3−-N、溶解无机氮(DIN)、PO43−-P、SiO32−-Si)的调查数据,解析了调查区域营养盐的分布特征,并结合悬浮物(TSM)等环境参数,探究其主要影响因素. 结果表明,NH4+-N、NO2−-N、NO3−-N、溶解无机氮(DIN)、PO43−-P、SiO32−-Si及悬浮物(TSM)的平均浓度(mg·L−1)分别为0.0246、0.00764、0.135、0.167、0.0256、0.576及16.8. 其中低于第四类海水水质标准的样品数量较低(<10%),表明该区域整体水质良好. NO3−-N、DIN及SiO32−-Si的平面分布具有保守性,其中NO3−-N与SiO32−-Si的平面分布由近岸到远洋呈逐渐降低趋势. 其原因是地处近岸区域受长江径流输入的影响所致. 而PO43−-P和NO2−-N的平面分布则显示为非保守性,其主要受所在区域海洋上升流及黑潮次表层水涌升影响. 尽管NH4+-N的分布呈现一定的保守性,且其平面分布趋势与NO3−-N与SiO32−-Si接近,但其高值点分析结果显示,除长江径流输入影响之外,人类活动亦对NH4+-N的分布具有明显影响.Abstract: Based on survey data of six nutrients including NH4+-N, NO2−-N, NO3−-N, dissolved inorganic nitrogen (DIN), PO43−-P and SiO32−-Si, and the related environmental parameters including total suspended matter (TSM) conducted in Summer, 2020, during the SPOHI Cruise, the distribution characteristics of nutrients were analyzed and the main influencing factors was discussed. The obtained results showed that the average concentrations (mg·L−1) of NH4+-N, NO2−-N, NO3−-N, DIN, PO43−-P, SiO32−-Si and TSM were 0.0246, 0.00764, 0.135, 0.167, 0.0256, 0.576 and 16.8, respectively. Among them, the number of samples which were below the fourth-class seawater quality was low (less than 10.0%). It indicated that the overall water quality in this investigated area was good. The planar distributions of NO3−-N, DIN and SiO32−-Si were conservative, and were gradually decreasing from the near shore area to the open ocean. The reason was that the investigated area was mainly affected by the input of the runoffs from the Yangtze River. However, the plane distributions of PO43−-P and NO2−-N were non-conservative, which were mainly affected by the upwellings in the area and the upwellings of the Kuroshio subsurface seawater. Additionally, the plane distribution of NH4+-N was conservative to a certain extent, and was close to those of NO3−-N and SiO32−-Si. However, based on the high value point measurement, it showed that the human activities also demonstrated an obvious effect on the its distribution, in addition to the impact of the Yangtze River runoff input.
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Key words:
- Yangtze River Estuary /
- nutrients /
- distribution characteristics.
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表 1 营养盐与TSM、盐度范围及均值
Table 1. The range and average of nutrients and TSM, salinity
项目
Projects浓度范围/(mg·L−1)
Concentration range平均浓度/(mg·L−1)
Average concentration总体
Total表层
Surface layer底层
Bottom layerNH4+-N 0.00550—0.0361 0.0246 0.0242 0.0255 NO2−-N ND—0.0392 0.00764 0.00849 0.00701 NO3−-N 0.00461—0.765 0.135 0.171 0.140 DIN 0.0286—0.780 0.167 0.204 0.173 PO43−-P ND—0.743 0.0256 0.0469 0.0197 SiO32−-Si ND—3.02 0.576 0.634 0.686 TSM ND—356.5 16.8 8.22 37.3 盐度 5.24—34.5 30.7 26.3 32.9 注:ND,未检出. ND, not detected. 表 2 调查海域的水质
Table 2. The quality of the investigation seawater
海水水质
Seawater quality以N计
Counting as N以P计
Counting as P样品数
Amounts百分比/%
Percent样品数
Amounts百分比/%
Percent一类水质 52 77.6 42 62.7 二类水质 7 10.4 — — 三类水质 1 1.50 17 25.4 四类水质及以上 7 10.4 8 11.9 表 3 营养盐与盐度、TSM之间的Pearson相关关系
Table 3. Pearson correlation coefficient between nutrients and salinity, TSM
营养盐
Nutrients相关系数
Correlation coefficient盐度
SalinityTSM NH4-N NO2-N NO3-N DIN PO4-P SiO3-Si NH4-N 0.419** 0.050 1 NO2-N -0.216 0.082 -0.098 1 NO3-N -0.803** 0.377** -0.390** 0.240 1 DIN -0.799** 0.384** -0.358** 0.279* 0.999** 1 PO4-P -0.037 -0.026 0.049 0.006 -0.026 -0.024 1 SiO3-Si -0.709** 0.340** -0.427** 0.217 0.891** 0.887** -0.059 1 注:**. 在0.01级别(双尾),相关性显著;*. 在0.05级别(双尾),相关性显著.
Note: **. At the 0.01 level (two-tailed), the correlation is significant; *. At the 0.05 level (two-tailed), the correlation is significant. -
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