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溶解氧 (dissolved oxygen, DO) 是我国地表水环境质量监测的重要指标之一,对维持水生生态系统健康具有重要意义[1-2]。水体中DO质量浓度波动变化受到耗氧和复氧的综合影响,耗氧主要包括水生生物呼吸耗氧、还原性污染物质耗氧、有机物降解耗氧[3-5],复氧主要包括大气复氧、水中浮游植物光合作用等[6-7]。水体中DO质量浓度受到多种因素的影响,水温、辐射、浊度和叶绿素a等环境因子的变化会影响上述耗氧和复氧两种作用,进而影响水体中DO的质量浓度[8-10]。当水体耗氧速率大于水体供氧速率时,DO无法及时补充,DO质量浓度逐渐降低。当DO质量浓度低于某一值时 (通常定义DO质量浓度低于4 mg∙L−1为低氧,低于3 mg∙L−1为缺氧,低于0.2 mg∙L−1为厌氧) ,水体中厌氧菌迅速繁殖,导致有机物快速分解从而出现腐败发酵的现象;水体黑臭、鱼类死亡,影响水生生物的生长,严重威胁水体生态安全[11]。水体脱氧已成为全球关注的重大生态环境问题[12-15]。目前对自然水体DO开展了大量研究,主要涉及DO动态变化规律研究、影响水体DO动态变化的因素研究等方面,以及沉积物耗氧[16-18]的相关研究。水体耗氧物质[19]有学者进行了研究,对于水体耗氧速率未见报道。
白洋淀是我国华北地区最大的以浅水淀泊为主的淡水湿地系统[20],是众多河流、淀泊、芦苇台田、浅沼、高地、沙洲与人类和谐共生发展而形成的独特的生态系统复合体。近年来,通过流域污染控制、入淀河流治理、内源生态清淤等措施,白洋淀水质得到极大改善,整体达到国家地表水Ⅲ类水质标准,但入淀河流影响区域6—10月出现DO质量浓度过低现象,DO质量浓度甚至低于2 mg∙L−1。针对白洋淀入淀河流影响区夏季水体缺氧问题,本研究通过自动监测站水质参数逐时数据的时间序列分析和水体耗氧实验模拟等方式,探究白洋淀入淀河流影响区DO时间变化特征、水体综合耗氧特征及相关影响因素,为白洋淀水环境治理和水生态修复提供决策依据。
白洋淀入淀河流影响区水体综合耗氧特征及影响因素
Integrated oxygen consumption characteristic and influencing factors in inflow river impact zone of Baiyangdian Lake
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摘要: 针对白洋淀入淀河流影响区夏季溶解氧 (DO) 浓度过低的现象,综合采用水质数据时间序列分析、水体综合耗氧实验模拟和相关性统计分析等方法深入研究了府河影响区的南刘庄国控断面溶解氧逐时变化规律、不同下垫面类型水体耗氧速率以及其影响因素。结果表明:1) 南刘庄断面DO质量浓度呈现出春秋季高夏季低的趋势,在水质逐年改善的背景下2022年夏季DO质量浓度仍低至1.5 mg∙L−1左右;DO质量浓度日变幅在0.5~5.7 mg∙L−1之间,均值为2.3 mg∙L−1,呈现出夏季>春季>秋季的状态;2) 府河影响区水体耗氧速率在0.024 0~0.049 9 mg∙(L∙h)−1之间,不同下垫面水域类型水体呈现水道≈淀面>沟壕的状态;不同深度水体基本呈现下层>上层和中层的趋势;水体综合耗氧速率中沉积物耗氧速率与水体耗氧速率的比值为1.55,水体和沉积物耗氧均是水体DO较低的重要原因;3) 南刘庄断面DO质量浓度年内变化趋势与叶绿素a (Chla) (p<0.01) 、浊度 (p<0.01) 和CODMn质量浓度 (p<0.01) 呈显著负相关关系;水体耗氧速率与叶绿素a (Chla) (p<0.01) 、DOC (p<0.05) 和CODMn质量浓度 (p<0.05) 呈显著正相关关系。降低河流来水浊度、抑制入淀河流影响区域夏季浮游藻类爆发增长、阶段开展生态清淤降低沉积物本身和孔隙水污染物扩散带来的高耗氧本底问题是白洋淀水质稳定达到Ⅲ类的根本保障。Abstract: Regarding the phenomenon of low dissolved oxygen (DO) concentration in the affected area of the Baiyangdian River during summer, this study employed time series analysis of water quality data, comprehensive oxygen consumption experiments on water bodies, and correlational statistical analysis to research the diurnal variation patterns of dissolved oxygen (DO) concentration at the Nanliuzhuang national control section within the Fu River's influence zone, the water oxygen demand over different underlying surface types, and their influencing factors during summer. The results showed that the DO concentration at the Nanliuzhuang section exhibited a seasonal pattern of higher levels in spring and autumn and lower levels in summer, with the concentration dropping to around 1.5 mg∙L−1 in summer of 2022 despite overall improvements in water quality over the years. The daily fluctuation range of DO concentration varied between 0.5~5.7 mg∙L−1, with an average of 2.3 mg∙L−1, showing a trend of summer > spring > autumn. The water oxygen demand in the Fu River's influence zone ranged from 0.024 0 to 0.049 9 mg∙(L∙h)−1, with the water bodies showing a pattern of canal ≈ lake surface > ditch in terms of different underlying surface water types. The water oxygen demand generally exhibited a trend of bottom layer > surface layer and middle layer across different depths. The ratio of sediment oxygen demand to water oxygen demand in the comprehensive oxygen consumption rates of water bodies was 1.55, indicating that both water and sediment oxygen demand significant reasons for the low DO concentration. The annual variation trend of DO concentration at the Nanliuzhuang section showed a significant negative correlation with chlorophyll a (Chla) content (p < 0.01), turbidity (p < 0.01), and CODMn concentration (p < 0.01), and the water oxygen demand was significantly positively correlated with chlorophyll a (Chla) content (p < 0.01), DOC concentration (p < 0.05), and CODMn concentration (p < 0.05). Reducing the turbidity of river inflows, suppressing the explosive growth of phytoplankton in the river inflow influence area during summer, and periodically conducting ecological dredging to reduce the high oxygen consumption background caused by sediment and pore water pollutant diffusion were fundamental to ensuring the stable achievement of Class III water quality standards in Baiyangdian Lake.
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表 1 南刘庄国控断面水质指标变化趋势相关性
Table 1. Correlation between changes in water quality indicators of Nanliuzhuang national control section
相关系数及显著性检验 指标 DO 浊度 Chla CODMn person相关性 DO 1 −0.598** −0.756** −0.473** 双尾检验 0.000 0.000 0.000 person相关性 浊度 −0.598** 1 0.892** 0.130** 双尾检验 0.000 0.000 0.000 person相关性 Chla −0.756** 0.892** 1 0.359** 双尾检验 0.000 0.000 0.000 person相关性 CODMn −0.473** 0.130** 0.359** 1 双尾检验 0.000 0.000 0.000 注:**表示在0.01水平下相关性显著 表 2 研究区域采样点位上覆水、沉积物基础理化指标
Table 2. Basic physicochemical indexes of overlying water and sediments at sampling sites in the study area
点位 上覆水基础指标 沉积物指标 T/ ℃ pH ORP/(mV) COND/(μS∙cm −1) TDS/(mg∙L−1) DO/(mg∙L−1) 浊度/NTU OM/% TP/(mg∙kg−1) TN/(mg∙kg−1) S1 17.7±0.7 7.57±0.02 89±1 539.2±0.8 368.2±0.9 2.13±0.5 7.47±0.29 8.30 1 390.30 2 993.72 S2 16.3±0.6 7.68±0.37 106±1 545.2±0.4 373.4±0.4 2.21±0.42 5.80±0.61 9.02 1 069.88 2 843.59 S3 18.3±1.3 8.46±0.23 101±5 547.1±2.8 373.1±2.9 1.84±0.97 2.69±0.12 9.94 1 106.29 4 279.20 点位 上覆水营养指标 TP/
(mg∙L−1)SRP/
(mg∙L−1)TN/
(mg∙L−1) /$ \text{N}{\text{O}}_{\text{3}}^{-}\text{-N} $
(mg∙L−1) /$ \text{N}{\text{H}}_{\text{4}}^{\text{+}}\text{-N} $
(mg∙L−1)Chla/
(ug∙L−1)DOC/
(mg∙L−1)BOD5/
(mg∙L−1)CODCr/
(mg∙L−1)CODMn/
(mg∙L−1)S1 0.41±0.06 0.12±0.09 1.92±0.14 0.93±0.04 0.32±0.15 10.78±1.40 9.82±2.18 0.23 11.67±1.53 4.01±0.03 S2 0.52±0.15 0.13±0.01 1.10±0.49 0.30±0.03 0.46±0.01 9.12±1.64 9.89±2.77 0.25 17.00±2.65 4.38±0.28 S3 0.37±0.03 0.06±0.01 0.84±0.05 0.19±0.13 0.02±0.00 9.89±3.01 13.13±1.24 0.25 7.33±0.58 3.88±0.18 -
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