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磷是自然水体的限制性营养元素之一[1],过剩的磷会导致水生生态系统初级生产力升高,进而导致水体富营养化,破坏水生生态系统平衡[2]。沉积物作为天然河道的组成部分,一方面,沉积物磷的赋存形态及含量、分布特征、迁移转化和吸附特性等影响着水体富营养化的进程[3];另一方面,在外源污染得到有效控制的同时,内源磷释放会成为主要的污染因子,导致水体富营养化[4]。影响磷在表层沉积物吸附释放的主要因素有沉积物组成粒径、各形态磷含量、腐殖质种类等沉积物本身的特性和pH、氧化还原电位、离子强度、温度等环境因素。目前,已经提出对沉积物不同形态磷的分析方法。朱广伟等[5]对沉积物不同形态磷进行了化学分级浸提,是目前比较系统的方法,该方法将沉积物中的磷分为7种形态,有效地分离了Fe/Al-P,减少后续投加富里酸对各形态磷影响研究的异议。
根据清远市人民政府网站公开数据,“十三五”期间漫水河黄坎桥断面水质为Ⅴ类-劣Ⅴ类,定类因子主要为总磷,而总磷质量浓度超标是造成水体富营养化的主要因素之一,从天地图可知,该流域污染源以畜禽养殖、农田及生活污水为主,其产生的废水富含有机物,排入河道会造成水体有机质含量上升[6]。
有机质作为大气二氧化碳和植物养分的来源以及连接土壤物理、化学和生物特性的主要因素,对其研究具有重要意义[7]。土壤有机质由生物化学组成、生物稳定性和碳周转率等各不相同的单元组成。腐殖化的有机质被称为腐殖质(腐殖酸HA、富里酸FA和胡敏素HA)[8],含有羧基、醇羟基、酚羟基等各种官能团。在腐殖质丰富的环境中,腐殖质与多种金属氧化物(Al2O3、Fe2O3、SiO2和TiO2等)通过络合、螯合和吸附等机理相互作用形成有机胶体,并随水体大量迁移,从而直接或间接影响土壤中磷酸盐的吸附和磷的有效性[9]。因此,本研究将通过模拟实验,向水环境中投加外源富里酸以探究腐殖质对沉积物中磷酸盐的吸附和磷有效性的影响。另外,有机质腐殖化是一个缓慢的过程,在实验过程中,添加外源富里酸可以在不等待有机质腐殖化的情况下增加有机质含量,是排除不同矿物组成和其他因素变化对实验结果造成影响的有效途径[10]。
目前,关于水体和沉积物营养盐污染的研究分析较多[11],对蓝藻、有机质等物质对沉积物磷形态迁移转化规律研究较为深入[12],也有研究者分析了FeO与腐殖质的结合机理[13]。但目前尚缺乏对腐殖质浓度影响沉积物总体磷形态迁移转化规律的研究。因此,本研究在已有研究的基础上,选取清远市清新区漫水河河段5条污染贡献比较高且污染来源不同的农灌渠作为研究对象,分析了其表层沉积物中磷的分布特征;通过投加外源富里酸探究了腐殖质浓度对沉积物各形态磷分布的影响,揭示了沉积物中各形态无机磷迁移转化的机制,以期为后续河道富营养化控制和内部养分负荷降解提供参考。
漫水河清远流域磷污染特征及富里酸对沉积物释磷的影响
Characteristics of phosphorus pollution in Manshui River and the effects of fulvic acid on phosphorus release from sediments
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摘要: 探讨了漫水河清新区境内流域上覆水和沉积物中磷的空间分布特征,以及富里酸含量对沉积物释磷的影响。结果表明:5条农灌渠水体总磷质量浓度为0.87~2.83 mg·L−1,超过地表水环境质量标准Ⅴ类水浓度限值;沉积物样本取自12个采样点,测得总磷含量为593.35~2 973.00 mg·kg−1,其中铁结合磷(Fe-P)占比最高,为19.54%~64.47%;沉积物各采样点生物有效磷分布差异较大,占总磷比例平均为57.73%,说明研究农灌渠的沉积物潜在释磷能力大。相关性分析结果表明,TP含量与Fe-P、闭蓄态磷(Oc-P)、自生磷(De-P)含量间呈显著正相关,表明外源磷输入是导致沉积物磷含量升高的主要原因。投加外源富里酸的模拟实验结果表明,富里酸浓度升高会提高沉积物对磷的吸附能力,进而促进Fe-P的形成。Abstract: In this study, the spatial distribution of phosphorus in the overlying water and sediments in the Qingxin District of the Manshui River was explored, and the effect of fulvic acid concentration on phosphorus release from sediments. The results showed that the total phosphorus concentrations at the 5 agricultural irrigation canals were 0.87~2.83 mg·L−1, which exceeded the surface water environmental quality standard V class water concentration limit; sediment samples were taken from 12 sampling points, the measured total phosphorus contents were 593.35~2 973.00 mg·kg−1, iron-bound phosphorus(Fe-P) accounted for the highest proportion of total phosphorus, which was 19.54%~64.47%; the distribution of biologically available phosphorus at each sampling point of the sediment was quite different, accounting for 57.73% of total phosphorus on average, which indicated that the potential release capacity of phosphorus from the sediments of the studied agricultural irrigation canals was large. The correlation analysis results showed that the significant positive correlations occurred between the content of TP and the content of Fe-P, closed storage state phosphorus(Oc-P), and authigenic phosphorus(De-P), indicating that the external source phosphorus input was the main reason for the increase of the phosphorus content of the sediment. The simulation experiment results of adding exogenous fulvic acid showed that the increase of the fulvic acid concentration could increase the adsorption capacity of the sediment for phosphorus, leading to Fe-P formation.
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Key words:
- phosphorus /
- sediment /
- sequential extraction /
- iron-bound phosphorus /
- fulvic acid
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表 1 不同采样点各形态磷浓度Fig.1 Phosphorus concentration of each form at different sampling sites
采样点
编号所属
农灌渠各形态磷浓度/(mg·L−1) TP TDP TPP SRP DOP L1 MT排涝 1.05 0.21 0.84 0.19 0.02 L2 MT排涝 1.08 0.33 0.75 0.27 0.06 L3 MT排涝 0.87 0.15 0.72 0.10 0.05 L4 MT排涝 1.43 0.53 0.90 0.51 0.02 L5 JK干渠 2.08 0.54 1.54 0.13 0.41 L6 JK干渠 1.66 0.62 1.04 0.47 0.15 L7 JK干渠 2.83 1.78 1.05 1.51 0.27 L8 JK干渠 2.34 1.13 1.21 0.82 0.31 L9 JK干渠 1.36 0.48 0.88 0.33 0.15 L10 JJ排坑 1.07 0.44 0.63 0.05 0.39 L11 XST排坑 1.76 0.74 1.02 0.06 0.68 L12 HYT排坑 2.39 1.17 1.22 0.47 0.70 表 2 表层沉积物总磷及不同赋存形态磷之间的Pearson相关性(n=12)
Table 2. Pearson correlation between total phosphorus in surface sediments and phosphorus in different forms(n=12)
TP Ex-P Al-P Fe-P Oc-P Ca-P De-P Or-P BAP TP 1 — — — — — — — — Ex-P 0.520 1 — — — — — — — Al-P 0.468 0.625* 1 — — — — — — Fe-P 0.939** 0.415 0.482 1 — — — — — Oc-P 0.833** 0.413 0.472 0.637* 1 — — — — Ca-P 0.575 0.248 -0.154 0.312 0.673* 1 — — — De-P 0.641* 0.240 -0.074 0.419 0.736** 0.762** 1 — — Or-P 0.490 0.508 0.245 0.315 0.590* 0.448 0.530 1 — BAP 0.944** 0.517 0.580* 0.991** 0.662* 0.295 0.400 0.359 1 注: **表示在P<0.01级别相关性显著;*表示在P<0.05级别相关性显著。 表 3 模拟实验相关条件参数
Table 3. Relevant condition parameters of simulation experiment
组别 土样
质量/g添加FA
体积/mL定容后溶液
体积/mLTOC质量浓度/
(mg·L−1)对照组 9.999 6 0 200 0 1 9.999 8 13 200 14.95 2 10.000 5 35 200 40.25 3 10.000 3 87 200 100.05 -
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