闽江入海断面溶解无机氮长时间序列分析及入海通量估算

为深入研究闽江口富营养化机制,于1985—2021年在闽江入海断面开展了水质监测。采用结合局部加权回归散点平滑法(LOWESS)的季节性肯达尔检验(SK检验)对断面溶解无机氮(DIN)及其各组分浓度变化趋势进行分析,同时结合水文资料对入海通量进行估算。结果表明:DIN浓度范围为0.728~3.140 mg/L,在37年间整体呈上升趋势,但不显著。各组分中NO₂-N和NH₃-N浓度分别呈显著和极显著下降趋势,而NO₃-N浓度呈极显著上升趋势。DIN组分中NO₂-N和NH₃-N比重不断减小,而NO₃-N比重不断增大,目前已成为DIN的主要组成部分。DIN入海通量范围为3.59×10⁴~14.85×10⁴ t,在37年间缓慢增加,其各组分入海通量长期变化趋势同浓度变化类似。从长期来看,DIN及其各组分浓度的变化趋势主要受流域环境变化及下游福州市含氮废水排放影响,而在短期则受台风、降水等一些突发环境事件的影响较大。

Long Time Series Analysis and Fluxes Estimation of Dissolved Inorganic Nitrogen in Section of River-Sea Boundary in Minjiang Estuary

In order to understand the mechanics of eutrophication in Minjiang estuary,water quality monitoring was carried out in section of river-sea boundary in Minjiang estuary from 1985 to 2021.Using seasonal Kendall test combined with LOWESS,the concentration variation trends of dissolved inorganic nitrogen (DIN) and its components were analyzed.Fluxes were also estimated with hydrological data.Results showed that the concentration of DIN range from 0.728 to 3.140 mg/L,with an overall upward trend but not significant during the 37 years.The concentrations of NO₂-N and NH₃-N revealed significant and highly significant downward trends relatively,while the concentration of NO₃-N revealed highly significant upward trend.For DIN components,the percentage of both NO₂-N and NH₃-N fell continuously while the percentage of NO₃-N raised,thus NO₃-N became dominant part of DIN in recent years.The flux of DIN into the sea ranged from 3.59×10⁴ to 14.85×10⁴ t,and raised slowly during the 37 years,and the long-term flux trends of its components were similar to that of the concentration.Variations of DIN and its components were mainly affected by environment changes in Minjiang River basin and nitrogenous wastewater discharged from Fuzhou City on a long-term basis,however it could be greatly affected by some environmental event (typhoon) on a short-term basis.