Photochemical and microbial alteration of chromophoric dissolved organic matter (CDOM) in aquatic ecosystems associated with different sources

Abstract

城市非点源污染向水生生态系统中输入大量的溶解有机物(DOM)，对生态系统健康产生重要影响. 有色可溶性有机物(CDOM)是广泛分布于自然水体中的一类成分和结构复杂、含有多种高活性化学官能团的大分子聚合物，是DOM的重要组分，对水生生态系统健康、能量流动及生物地球化学循环有重要影响. 光化学反应和微生物代谢过程被认为是控制水体CDOM转化、降解和循环的主要影响因素. 然而，对城市化如何影响CDOM组成以及光化学和微生物如何相互作用影响城市水体CDOM动态的理解是不足的. 因此，为评估光化学过程和微生物代谢对不同城市水体CDOM降解与转化的贡献，解析不同城市水体CDOM光化学/微生物降解作用机理，本研究在英国伯明翰选择3类具有典型DOM来源的水体样本，通过实验室9 d受控培养实验，对比分析光化学以及微生物影响下CDOM来源和组成的变化. 结果表明：(1)城市河流由于接受上游污水排放及较短的水力滞留时间，含有丰富的芳香性碳，其CDOM光化学活性明显高于湖泊，光化学降解率为16.60%;(2)城市湖泊CDOM受人类活动影响，自生源类荧光成分富集，生物活性高，在微生物培养过程中CDOM增加了62.16%，而相较于城市湖泊，非城市湖泊由于接受周围景观土壤输入的大量腐殖质类CDOM，光照对其降解转化作用较为明显; (3)光化学过程促进了陆源CDOM中大分子类腐殖质物质降解成为生物活性高的小分子化合物，刺激微生物代谢生成类蛋白质类有机物; 以类蛋白质组分为主导的CDOM在光照过程中被转化为难降解状态，生物活性降低，CDOM微生物代谢过程被抑制. 研究成果为城市水体不同CDOM来源及活性差异特征研究提供了新的思路，有助于城市河流的可持续开放与管理.;Urban non-point source pollution contributes large amounts of dissolved organic matter (DOM) to aquatic ecosystems and has a significant impact on ecosystem health. Chromophoric dissolved organic matter (CDOM) is a group of macromolecular polymers with complex composition and structure, containing a variety of highly reactive chemical functional groups, which are widely distributed in natural waters. It has an important impact on aquatic ecosystem health, energy flow and biogeochemical cycling. Photochemical reactions and microbial metabolic processes are the main controlling factors on the transformation, degradation and cycling of CDOM in water bodies. However, understanding how urbanization source input impacts CDOM quantity and quality and how photochemical and microbial interact to affect CDOM dynamic are deficient. To assess the contribution of photochemical processes and microbial metabolism to the degradation and transformation of different sources of CDOM in urban waters, and to elucidate the mechanisms of photochemical/microbial degradation of different sources of CDOM in aquatic systems (non-urban lake with humic, mostly terrestrial CDOM; urban lake with autochthonous biological production CDOM; urban river with mixed humic and protein-like CDOM), this study compares and analyses the changes in the sources and composition of CDOM under the influence of photochemistry and microorganisms in a controlled 9-day laboratory incubation experiment in three water bodies with typical urban characteristics, selected in Birmingham, UK. Changes in CDOM concentration, optical properties and chlorophyll concentration were measured at the initial and end of incubations. The results show that: (1) due to the acceptance of upstream sewage discharge and shorter hydraulic retention times, the CDOM of urban rivers is dominated by aromatic substances, with the highest photochemical degradation rate of 16.60%; (2) the CDOM of urban lakes, which is affected by human activities, is dominated by autochthonous substances, and could be increased by 62.16% via microbial metabolism, while compared to urban lakes, non-urban lakes have a more pronounced effect of light on their degradation and transformation due to receiving a large input of humus-like CDOM from the surrounding landscape soils; (3) the photochemical process could degrade terrestrial humic-like substances into small molecular compounds with high biological activity, which could stimulate microbial metabolism to produce protein-like CDOM, however, photochemical degradation could inhibit microbial metabolism by transform the autochthonous protein-like CDOM into a refractory state. The study provides a novel perspective for the differences in the sources and activities of CDOM in different urban aquatic systems and the changes in CDOM characteristics during photochemical and microbial processes.