2016—2021年长江口海域营养盐时空变化特征及其影响因素研究
Spatial-Temporal Characteristics of Nutrients in the Yangtze River Estuary and Its Influencing Factors from 2016 to 2021
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摘要: 为研究长江口海域营养盐时空变化特征及其主要影响因素，本文基于2016—2021年长江口生态环境监督性监测数据、长江流域入海断面监测数据以及长江径流数据，根据长江口盐度(S)空间分布特点，将该海域分为淡水区(S＜5‰)、河口区(5‰＜S＜25‰)和海水区(S＞25‰)，从分区的角度探讨长江口海域无机氮、磷酸盐、硅酸盐时空分布、营养盐结构及限制因子。结果表明：①时间上，2016—2021年DIN、PO4-P浓度呈波动下降趋势，SiO3-Si则呈波动上升趋势。DIN主要表现为春季＞夏季＞秋季，PO4-P和SiO3-Si则呈现秋季＞夏季＞春季的趋势。②空间上，DIN、SiO3-Si都是由近岸向远海逐渐递减的趋势，呈现出淡水区＞河口区＞海水区的分布特征；PO4-P则表现为河口区＞淡水区＞海水区。DIN、PO4-P、SiO3-Si都受到长江冲淡水的影响。PO4-P高值区通常位于最大浊度带附近，悬浮颗粒物在一定程度上影响PO4-P的分布情况。浮游植物的生长繁殖是营养盐含量变化的重要原因之一。③长江口海域营养盐结构具有分布不均衡的特点，N/P、Si/P均远大于16:1，Si/N则均接近1，P即为长江口海域浮游植物潜在限制因子。叶绿素a的相对高值区域大都处于P限制，Chla含量越高，N/P和Si/P则普遍越大，生物的吸收作用会使P的限制程度加剧，说明浮游植物对长江口海域营养盐结构具有重要的影响。研究显示：长江口海域营养盐分布具有明显的规律性，长江冲淡水对营养盐的空间分布有着重要影响。浮游植物的吸收作用是营养盐及其结构的影响因素之一。该研究结果可为长江口生态环境改善提供依据。Abstract: According to the partition method, the water quality and ecological monitoring data of the Yangtze River Estuary from 2016 to 2021 was used to analyze the spatial-temporal characteristics of nutrients and its influencing factors, while the study area was divided into freshwater zone (S < 5‰), estuary (5‰ < S < 25‰) and seawater zone (S > 25‰). The results indicated that, (1) The concentrations of DIN and PO4-P showed fluctuating downward trends, and SiO3-Si showed fluctuating upward trends from 2016 to 2021. The concentration of DIN mainly showed a trend of spring>summer>autumn, while PO4-P and SiO3-Si were opposite. (2) Affected by the freshwater from the Yangtze River, the concentration of DIN and SiO3-Si showed a trend of freshwater zone > estuary > seawater zone, while the PO4-P showed highest concentration in the estuary. The area with high PO4-P value was usually located near the maximum turbidity zone. The growth and reproduction of phytoplankton was one of the most important reasons for nutrients. (3) The nutrient structure of the Yangtze River Estuary was characterized by an uneven distribution, with N/P and Si/P much larger than 16:1, and Si /N close to 1. P was a potential limiting factor for phytoplankton. The relatively high value area of chlorophyll a was mostly limited by P, with high N/P and Si/P generally. The absorption of organisms will exacerbate the degree of P limitation, which indicated that phytoplankton have an important impact on the nutrient structure. Research showed that, the distribution of nutrients in the Yangtze River Estuary had obvious regularity, and the freshwater from the Yangtze River had an important influence on the spatial distribution of nutrients. The absorption of phytoplankton was one of the influence factors of nutrient structure. The results of the study can provide a basis for the improvement of the ecological environment of the Yangtze River estuary.
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