Limited degradability of dissolved organic carbon, nitrogen, and phosphorus during contrasting seasons in a tropical coastal environment

IF 3.8 1区 地球科学 Q1 LIMNOLOGY
Jiangyong Chu, Christian Lønborg, Patrick Martin
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Abstract

The biogeochemistry of dissolved organic matter (DOM) is poorly understood in tropical coastal waters. Here, we quantified the biological and photochemical lability of dissolved organic carbon, nitrogen, and phosphorus, in the tropical coastal waters of Singapore. We conducted experiments during the inter-monsoon, the mid-southwest monsoon, and the late southwest monsoon seasons, which span the greatest range of biogeochemical conditions found in the area. The DOM lability was quantified as concentration changes during 90-d biodegradation and 7-d photoreactor incubations. Overall, DOM showed low lability, even though dissolved organic nitrogen and dissolved organic phosphorus accounted for most of the dissolved nitrogen and phosphorus. In the biodegradation experiments, only 5–15% of dissolved organic carbon, 0–7% of dissolved organic nitrogen, and 8–21% of dissolved organic phosphorus were degraded. The addition of labile dissolved organic carbon, intended to test priming effects and to ensure the microbes were not carbon-limited, had no measurable impact on the results. During our photochemical experiments only 2–10% of the dissolved organic carbon were degraded, while neither dissolved organic nitrogen nor dissolved organic phosphorus showed consistent photochemical losses. The DOM optical properties (absorbance and fluorescence spectra) showed limited or no changes during the biodegradation experiments but larger declines in the photochemical experiments. Overall, the biodegradation of DOM was highest during the inter-monsoon, when autochthonous DOM was most dominant, while photolability was greater during the terrestrial DOM-rich southwest monsoon. Our results illustrate that in some tropical coastal environments, DOM can be fairly resistant to biological and photochemical degradation, and thus does not represent a large stock of potentially available nutrients.

Abstract Image

在热带海岸环境的不同季节,溶解的有机碳、氮和磷的有限降解性
热带沿海水域溶解有机物(DOM)的生物地球化学研究尚不清楚。在这里,我们量化了新加坡热带沿海水域中溶解有机碳、氮和磷的生物和光化学不稳定性。我们在季风间、西南季风中期和西南季风后期进行了实验,这些季节跨越了该地区发现的最大范围的生物地球化学条件。DOM的稳定性被量化为在90天的生物降解和7天的光反应器孵育期间的浓度变化。总体而言,DOM表现出较低的不稳定性,尽管溶解有机氮和溶解有机磷占溶解氮和磷的大部分。在生物降解实验中,溶解有机碳仅降解5-15%,溶解有机氮仅降解0-7%,溶解有机磷仅降解8-21%。添加不稳定的溶解有机碳是为了测试启动效应并确保微生物不受碳限制,但对结果没有可测量的影响。在我们的光化学实验中,溶解的有机碳只有2-10%被降解,而溶解的有机氮和溶解的有机磷都没有表现出一致的光化学损失。DOM的光学性质(吸光度和荧光光谱)在生物降解实验中变化有限或没有变化,但在光化学实验中下降较大。总体而言,DOM的生物降解在季风间期最高,本地DOM占主导地位,而光敏性在陆源DOM丰富的西南季风期更大。我们的研究结果表明,在一些热带沿海环境中,DOM可以相当抵抗生物和光化学降解,因此并不代表潜在可用营养物质的大量库存。
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来源期刊
Limnology and Oceanography
Limnology and Oceanography 地学-海洋学
CiteScore
8.80
自引率
6.70%
发文量
254
审稿时长
3 months
期刊介绍: Limnology and Oceanography (L&O; print ISSN 0024-3590, online ISSN 1939-5590) publishes original articles, including scholarly reviews, about all aspects of limnology and oceanography. The journal''s unifying theme is the understanding of aquatic systems. Submissions are judged on the originality of their data, interpretations, and ideas, and on the degree to which they can be generalized beyond the particular aquatic system examined. Laboratory and modeling studies must demonstrate relevance to field environments; typically this means that they are bolstered by substantial "real-world" data. Few purely theoretical or purely empirical papers are accepted for review.
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