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对于草型湖泊型湿地,水生植物生长发育与环境相互作用改变水体的理化性质[1],从而加速水体营养盐的快速氧化分解[2]。水生植物在水生生态系统的营养循环、能量流动和水质净化方面发挥重要作用[3]。然而,水生植物进入衰亡腐败期,形成凋落物会积存于湖泊水体中[4]。凋落物腐败分解是水生生态系统发生的一个自然过程,分解释放的营养物质释放到上覆水中,迁移吸附至沉积层逐渐累积,且未完全分解的凋落物堆积在沉积物中,将直接影响水环境状况[4-5]。
凋落物分解过程中的养分释放及其对水环境的影响已有不少研究。王晓栋[6]研究了南四湖主要水生植物菹草、水花生、莲、香蒲和芦苇分解过程中主要污染物的释放规律,估算发现每年430.92 ×104 t水生植物分解总有机碳(total organic carbon, TOC)、TN、NH4+-N和TP最大释放量分别为56 245.73、14 145.82、3 945.38和1 575.46 t。WU等[7]研究发现,水葫芦、黑藻和香蒲凋落物分解造成水体处于厌氧状态,释放大量的TOC、TN、NH4+-N和TP显著影响水环境质量,尤其是对水体DO和TOC的影响最显著。此外,YUAN等[8]研究表明,水生植物分解可产生大量的DOM,水中过量的DOM会导致溶解氧量和污染率增加[9],对水质造成潜在风险。
DOM由两类不同分子特征的混合物组成[10],一类是较易降解的氨基酸、酚类和有机酸等蛋白类物质,另一类是较难降解的类腐殖酸和类富里酸物质[11]。不同凋落物分解产生的DOM组分和含量不同[11-12],导致水体有机物污染程度不同[13]。因此,DOM组分和含量对上覆水水质有重要影响。WU等[14]研究发现香蒲凋落物分解过程上覆水中DOM质量浓度随着生物量增加而升高。ZHANG等[12]研究发现不同生物量凋落物分解产生的DOM组分和含量不同。然而,较少研究不同生物量凋落物分解过程中DOM的释放过程和结构特征的变化,以及其对水体有机物污染的影响程度。
水生植物的生物量和种类决定了植物自身营养物质含量不同,会导致其凋落物分解释放的DOM特性不同。沉水植物、浮游植物和挺水植物广泛分布于湿地水生生态系统,对水生生态系统产生重大影响。因此,以金鱼藻、菹草、浮萍和睡莲为代表进行分解实验,分析不同生物量凋落物分解过程中DOM的释放特征以及COD释放量与分解时间的关系,预测凋落物分解对水体有机物污染影响程度。研究结果可为水质恢复中湿地植物的种植密度和植物凋落物管理提供技术指导。
不同种类水生植物分解过程中溶解性有机物的释放特征
Release characteristics of dissolved organic matter during decomposition of different aquatic plants
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摘要: 为研究水生植物分解对水体有机物污染的影响,对不同生物量(0.1、0.5、1.0 g·L−1)下金鱼藻、菹草、浮萍和睡莲凋落物分解过程中溶解性有机物(dissolved organic matter, DOM)的释放特征进行了研究。结果表明,不同生物量下4种水生植物分解过程中上覆水DOM质量浓度变化趋势相似,0~15 d迅速增加,15~60 d缓慢下降直至相对稳定。有机物释放量为浮萍>睡莲>菹草>金鱼藻,DOM芳香化程度为菹草>睡莲>浮萍>金鱼藻。0~15 d,DOM以易降解的类蛋白有机物为主,此时COD释放量显著增加;30~60 d,难降解的类富里酸和类腐殖酸有机物含量逐渐增加,对COD贡献不明显。DOM质量浓度随着生物量的增加而逐渐增加。高生物量(≥0.5 g·L−1)凋落物分解体系易降解的类蛋白物质(0~15 d)与难降解的类富里酸、类腐殖酸有机物(30~60 d)含量显著增加。分析发现植物凋落物生物量、种类以及凋落物分解时期可影响DOM质量浓度和特性,进而可能影响水体有机物的污染状况。因此,为避免大量植物凋落物分解造成的潜在风险,应及时控制水体中植物凋落物量。Abstract: In order to study the effect of decomposition of aquatic plants on organic matters pollution in water body, the release characteristics of dissolved organic matter during the decomposition of litters of Ceratophyllum demersum L., Potamogeton crispus L., Lemna minor L. and Nymphaea tetragona L. at different biomass levels (0.1, 0.5, 1.0 g·L−1) were investigated. Results suggested that the variation trend of DOM mass concentration in the overlying water was similar during decomposition process of four aquatic plants with different biomass levels, a rapid increase from 0 to 15 d followed by a slow decrease until relatively stable from 15 to 60 d.The release of organic matters was Lemna minor L.>Nymphaea tetragona L.>Potamogeton crispus L.>Ceratophyllum demersum L., and the humification degree of DOM was Potamogeton crispus L.>Nymphaea tetragona L.>Lemna minor L.>Ceratophyllum demersum L. From 0 to 15 d, DOM was dominated by the easily biodegradable protein-like organic matters, and COD release increased significantly. From 30 to 60 d, the amount of the difficultly biodegradable fulvic acid-like and humic acid-like organic matters increased gradually, while their contribution to COD was not obvious. DOM mass concentration increased gradually with the increase of biomass levels. In high biomass (≥0.5 g·L−1) litter decomposition system, the content of easily biodegradable protein-like organic matters (0~15 d) and difficultly biodegradable fulvic acid-like and humic acid-like organic matters (30~60 d) increased significantly. The results showed that biomass levels, species and decomposition period of plant litters affected the mass concentration and characteristics of DOM, then they affect organic matters pollution of water body. Therefore, to avoid the potential risk caused by a large number of plant litter decomposition, the amount of plant litter in water body should be controlled in time.
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Key words:
- aquatic plants /
- biomass levels /
- dissolved organic matter /
- release characteristics
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表 1 植物凋落物中C和N含量
Table 1. Contents of C and N in plant litters
植物凋落物 C/% N/% C/N 金鱼藻 37.53±0.59 3.19±0.28 12:1 菹草 39.33±1.03 3.83±0.34 10:1 浮萍. 40.04±0.18 2.03±0.01 20:1 睡莲 39.46±0.86 3.39±0.11 11:1 -
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