2021年杭州湾及其邻近海域秋季营养盐分布特征和混合行为

Nutrients distribution and mixing behavior at Hangzhou Bay and its adjacent seain autumn 2021

营养盐是构成海洋生物资源的物质基础,也是我国近岸海域最主要的污染因素。本文基于2021年9月杭州湾及其邻近海域的调查资料,分析了该海域营养盐的形态、结构和分布特征,探讨了营养盐污染的潜在来源及影响因素。结果表明,总氮(total nitrogen,TN)平均浓度为1153μg/L,硝酸盐氮(NO3-N)和溶解性有机氮(dissolved organic nitrogen,DON)是氮元素的主要形态,分别占TN的40.9%和39.1%;总磷(total phosphorus,TP)平均浓度为112μg/L,颗粒态磷(particulate phosphorus,PP)是磷元素的主要形态,占TP的61.7%。在空间分布上,各形态营养盐整体上呈现由近岸向远岸浓度梯度降低的趋势;嵊泗海域表、底层浓度差异明显。除颗粒态营养盐比值(氮磷比)小于16外,其他各形态营养盐比值远高于16,调查海域呈现显著的磷限制。NO3-N、无机氮(dissolved inorganic nitrogen,DIN)、溶解性总氮(dissolved total nitrogen,DTN)、TN与盐度的相关系数分别为0.757、0.736、0.693、0.710,呈现保守行为,浓度变化主要由咸淡水混合过程控制;氨氮(NH4-N)、亚硝酸盐氮(NO2-N)、DON及磷的各种形态与盐度相关系数均小于0.5,呈现非保守行为,其浓度变化受河流输入、陆源污染、海水养殖及生物地球化学循环过程等多种因素的共同作用。

Nutrients are essential elements for phytoplankton growth and also are the main pollution elements in China’s coastal waters.Based on the investigation of Hangzhou Bay and its adjacent sea in September of 2021,the structure and distribution characteristics of nutrients,the potential pollution sources of seawater were explored.According to the results,the average concentration of total nitrogen(TN)was 1153μg/L and the main components of nitrogen were NO3-N and dissolved organic nitrogen(DON)with the proportions of 40.9%and 39.1%,respectively.The average concentration of total phosphorus (TP) was 112 μg/L and the main components of phosphorus was particulate phosphorus (PP) with theproportion of 61.7%. Nutrients spatial distribution of surface water showed that the concentrations decreasedgradually from nearshore to offshore, and nutrients distributions of bottom layer in Shengsi area weresignificantly different with surface layer. The vast majority of N/P ratios (except PN/PP) were generally greaterthan 16 indicating P-limited. Concentrations of NO3-N, dissolved inorganic nitrogen (DIN), DTN and TN werepositively correlated with salinity (correlation coefficient were 0.757, 0.736, 0.693 and 0.710) which indicatedtheir behaviors were conservative, and the concentrations were mainly controlled by the mixing with seawater.Correlation coefficients of NH4-N, NO2-N, DON and phosphorus were less than 0.5, which indicated theirbehaviors were non-conservative. Their concentrations were affected by river input, human activities, offshoreinput and biogeochemical cycle.