江苏盐城近海富营养化评价与径流输入的影响

依据2018年江苏盐城近岸海域的营养盐和化学需氧量（COD）等调查数据，采用单因子污染指数法、营养盐结构和限制性分析、富营养化状态指数法等对水域营养盐状况与富营养化特征进行了系统分析和评价。同时，对近岸4条主要河流的溶解无机氮（DIN）、溶解无机磷（DIP）和COD入海通量进行了估算，并探讨了陆源输入对近岸海域的影响。结果表明，该区水体DIN和DIP含量劣于第Ⅲ类海水水质标准的站位占比分别为90%和71%，但COD污染并不显著，78%的调查站位水体COD符合或优于国家Ⅰ类海水水质标准。水体营养盐与COD含量的空间分布趋势相似，表现为近岸高、离岸低、河口与港口局部区域异常高。调查区富营养化极为严重，98%的调查站位富营养化状态指数（E）≥1，重度富营养化（E＞10）的站位占比约30%。水体N/P平均为34，远高于Redfield比值，氮磷比例严重失衡，藻类生长可能会受到磷的潜在限制。经估算，近岸4条主要河流年DIN、DIP和COD的入海总量分别为12 901、484和33 077 t，为近岸海域污染物的主要来源；且各项污染物丰水季通量约为枯水季2倍；丰水季河流水体N/P比平均约为24.7，N污染较为严重，可能是造成夏季近岸海域氮磷比例失衡的重要原因之一。

Evaluation of eutrophication and impact of river runoff along the coastal zone of Yancheng City,Jiangsu Province

Based on in-situ investigation of water nutrients and chemical oxygen demand （COD） along the coast of Yancheng City, Jiangsu Province in 2018, nutrient concentrations, compositions, and spatial distributions were analyzed using single factor pollution index, nutrient ratios, and nutrient limitation. The related eutrophication status was evaluated using eutrophication state index. Meantime, the fluxes of dissolved inorganic nitrogen （DIN）, dissolved inorganic phosphorus （DIP）, and COD discharged into coast from four local rivers were calculated, and their impacts on the coast were discussed. Results show that DIN and DIP contents in 90% and 71% of sampling stations, respectively, were higher than the Class III seawater quality standard of China, showing apparent DIN and DIP pollutions. Comparatively, COD pollution was not significant because COD contents in 78% of sampling stations were below the Class I seawater quality standard. Spatial distribution patterns of water nutrient and COD were similar, and their contents decreased from nearshore to offshore in general, but increased sharply in some estuaries and ports. The eutrophication in the study area was very serious, because sampling stations with eutrophication state index （E）≥1 accounted for 98%, and stations with severe eutrophication （E>10） accounted for about 30%. Water N/P ratios were about 34 on average, much higher than the Redfield ratio, implying nutrient composition was seriously unbalanced, and algal growth might be potentially limited by phosphorus. Annual fluxes of DIN, DIP, and COD from four inflowing rivers into the coast were estimated to be 12 901, 484, and 33 077 t, respectively, which were the main pollutant sources of coastal waters. In addition, their fluxes in the wet season were about twice higher than those in the dry season, and N/P ratios of river runoff in the wet season were 24.7 in average, suggesting the serious N pollution, which was possibly the major reason for the imbalance of nitrogen and phosphorus in the coastal waters.