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水体富营养化及蓝藻水华仍然是目前湖泊、水库所面临的最主要的生态环境问题[1]。据生态环境部最新发布的《2020中国生态环境状况公报》显示,开展水质监测的112个重要湖库中IV-V类、劣V类水质占23.2%,总磷是主要污染指标之一;110个监测营养状态的湖库中,轻度富营养状态、中度富营养状态和重度富营养状态占29.0%,湖库富营养化态势严峻[2]。在湖库生态系统中,沉积物作为碳、氮、磷等营养元素和其他污染物的主要蓄积库,在外源污染得到有效控制的情况下,沉积物的内源释放依旧会导致严重的富营养化问题[3]。因此在湖库富营养化防治过程中,沉积物中的碳、氮、磷是备受关注的重要指标。
对河流、湖泊沉积物中氮磷等营养盐含量及其分布特征目前已经开展了较多的研究[4-5]。近年来,水库逐渐成为城市供水的主要水源[6]。相较于天然湖泊,水源水库水体停留时间更长,对污染物的截留沉积效果更加明显[7]。同时,由于季节性热分层的存在,导致水库底层水体长期处于厌氧或者缺氧状态,诱发沉积物营养物质释放,造成水库蓝藻水华爆发,严重危及饮用水安全[8-9]。因此,探明水源水库沉积物中碳、氮、磷的污染负荷及分布特征,揭示其污染现状,对水库水体富营养化控制、保障饮用水安全具有重要意义。
随着深圳经济的高速发展和用水需求的不断增长,水安全问题备受关注。茜坑水库作为深圳市西北片区最重要的饮用水水库,对经济发展和社会稳定有着重要作用[10-11]。目前,对茜坑水库表层沉积物中碳、氮、磷污染状况还缺乏系统的调查。本研究通过采集茜坑水库14个点位表层沉积物,测定各点位表层沉积物总有机碳(TOC)、总氮(TN)、总磷(TP)的含量,研究表层沉积物中TOC、TN、TP空间分布特征,分析TOC、TN、TP的相关关系和TOC/TN,沉积物的污染状况采用综合污染指数法和有机指数法进行评价。
水源水库沉积物碳氮磷分布特征及污染评价
Distribution characteristics of carbon, nitrogen and phosphorus in sediments of water source reservoir and pollution assessment
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摘要: 茜坑水库作为深圳市重要的水源水库,对当地经济发展和社会稳定有着重要作用。为探究茜坑水库沉积物中营养物质的空间分布特征及污染状况,测定了茜坑水库14个点位表层沉积物中总氮(TN)、总磷(TP)和总有机碳(TOC)的含量,分析了TN、TP、TOC之间的相关性及TOC/TN,并对沉积物污染状况进行了评价。结果表明,茜坑水库表层沉积物TN平均含量为3442 mg·kg-1,TP平均含量为1648 mg·kg-1,TOC平均含量为1.477%,碳、氮、磷污染严重且空间分布差异明显,旧库区主库及库湾碳、氮、磷含量均大于新库区。相关性分析表明,TOC与TN、TOC与TP、TN与TP均呈显著正相关关系(P<0.05,r2分别为0.95, 0.63, 0.69),表明茜坑水库表层沉积物氮磷多以有机形式存在,且氮磷具有同源性。TOC/TN表明茜坑水库沉积物中的有机质多来自于藻类,还有一小部分来自水生生物。综合污染指数和有机指数评价结果均表明茜坑水库各个点位沉积物污染程度严重,氮、磷、有机质具有潜在的内源释放的风险。Abstract: As an important water source reservoir in Shenzhen, Xikeng Reservoir plays an important role in local economic development and social stability. To explore the spatial distribution characteristics and pollution status of nutrients in the sediments of the Xikeng Reservoir, this study determined the total nitrogen (TN), total phosphorus (TP) and total organic carbon (TOC) of the surface sediments at 14 points in the Xikeng Reservoir, analyzed the correlation between TN, TP, TOC and TOC/TN, and evaluated the sediment pollution. The results showed that the average content of TN in the surface sediments of Xikeng Reservoir was 3442 mg·kg-1, the average content of TP was 1648 mg·kg-1, the average content of TOC was 1.477%, the pollution of carbon, nitrogen, and phosphorus was serious and the spatial distribution difference was obvious. The carbon, nitrogen and phosphorus contents of the main reservoir and reservoir bay in the old reservoir area were higher than those in the new reservoir area. The correlation showed that TOC and TN, TOC and TP, TN and TP were all significantly positively correlated (P<0.05, r2 was 0.95, 0.63, 0.69, respectively), indicated that the nitrogen and phosphorus in the surface sediments of Xikeng Reservoir mostly existed in organic form, and nitrogen and phosphorus had homology. TOC/TN indicated that the organic matter in the sediments of Xikeng Reservoir mostly came from algae, and a small part came from aquatic organisms. The evaluation results of the comprehensive pollution index and the organic index indicated that the sediment pollution at each point of the Xikeng Reservoir was serious, and there were potential risks of internal release of nitrogen, phosphorus, and organic matter.
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表 1 采样点位置及表层沉积物性状
Table 1. Sampling point location and sediments properties
点位
Point位置
Location泥质
Sediment qualityXK1 坝前最深点 表层颜色较浅,内层发黑,泥较黏稠 XK2 入水口 颜色很浅,沙砾较多,臭味大 XK3 旧库区库湾 颜色深黑,有臭味 XK4 入水口 沙砾最多,颜色最浅 XK5 旧库区主库 内层颜色发黑,泥呈松散稀软状 XK6 旧库区库湾 表层颜色较浅,内层发黑,泥较黏稠 XK7 旧库区库湾 内层颜色发黑,泥呈松散稀软状 XK8 旧库区库湾 内层颜色深黑 XK9 旧库区主库 内层颜色发黑,泥呈松散稀软状 XK10 出水口 内层颜色发黑,泥呈松散稀软状 XK11 新库区主库 表层颜色较浅,内层发黑 XK12 新库区主库 颜色深黑,有臭味 XK13 新库区主库 有少许沙砾,内层颜色较黑 XK14 新库区库湾 内层颜色发黑,泥呈松散稀软状 表 2 茜坑水库表层沉积物TN、TP、TOC相关关系
Table 2. Correlation of TN, TP and TOC in surface sediments of Xikeng Reservoir
TOC TN TP TOC 1 TN 0.95* 1 TP 0.63* 0.69* 1 表 3 沉积物污染评价标准[24]
Table 3. Standard of pollution for sediments
等级
Grade综合污染指数
Comprehensive pollution index有机污染指数
Organic pollution index污染程度
Pollution degreeSTN STP FF 有机指数
Organic index有机氮/%
Organic nitrogen1 <1.0 <0.5 ≤1.0 <0.05 <0.033 未受污染 2 1.0—1.5 0.5—1.0 1.0—1.5 0.05—0.2 0.033—0.066 轻度污染 3 1.5—2.0 1.0—1.5 1.5—2.0 0.2—0.5 0.066—0.133 中度污染 4 ≥2.0 ≥1.5 ≥2.0 ≥0.5 ≥0.133 重度污染 表 4 茜坑水库表层沉积物污染评价结果
Table 4. Evaluation results of surface sediment pollution in Xikeng Reservoir
点位
PointSTN 污染程度
Pollution
degreeSTP 污染程度
Pollution
degreeFF 污染程度
Pollution
degree有机指数
Organic
index污染程度
Pollution
degree有机氮指数
Organic nitrogen
index污染程度
Pollution
degreeXK1 5.14 重度 3.95 重度 4.85 重度 0.53 重度 0.33 重度 XK2 2.02 重度 2.64 重度 2.49 重度 0.05 轻度 0.13 中度 XK3 6.38 重度 3.58 重度 5.72 重度 0.87 重度 0.41 重度 XK4 3.51 重度 2.69 重度 3.31 重度 0.24 中度 0.22 重度 XK5 5.81 重度 5.16 重度 5.65 重度 0.59 重度 0.37 重度 XK6 6.38 重度 5.72 重度 6.22 重度 0.77 重度 0.41 重度 XK7 6.77 重度 4.90 重度 6.32 重度 0.84 重度 0.43 重度 XK8 6.66 重度 3.45 重度 5.92 重度 0.76 重度 0.42 重度 XK9 5.92 重度 4.69 重度 5.62 重度 0.54 重度 0.38 重度 XK10 4.57 重度 2.44 重度 4.08 重度 0.30 中度 0.29 重度 XK11 5.92 重度 5.39 重度 5.79 重度 0.71 重度 0.38 重度 XK12 5.81 重度 3.25 重度 5.21 重度 0.66 重度 0.37 重度 XK13 2.23 重度 2.08 重度 2.20 重度 0.07 轻度 0.14 重度 XK14 4.79 重度 2.19 重度 4.19 重度 0.48 中度 0.30 重度 表 5 茜坑水库表层沉积物TN、TP、TOC平均含量与其他湖库比较
Table 5. Comparison of the average content of TN, TP and TOC in the surface sediments of Xikeng Reservoir with other lakes and reservoirs
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