Divergent metabolism estimates from dissolved oxygen and inorganic carbon: Implications for river carbon cycling

IF 3.8 1区 地球科学 Q1 LIMNOLOGY
Qipei Shangguan, Robert A. Payn, Robert O. Hall Jr, Fischer L. Young, H. Maurice Valett, Michael D. DeGrandpre
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Abstract

Rivers efficiently collect, process, and transport terrestrial-derived carbon. River ecosystem metabolism is the primary mechanism for processing carbon. Diel cycles of dissolved oxygen (DO) have been used for decades to infer river ecosystem metabolic rates, which are routinely used to predict metabolism of carbon dioxide (CO2) with uncertainties of the assumed stoichiometry ranging by a factor of 4. Dissolved inorganic carbon (DIC) has been less used to directly infer metabolism because it is more difficult to quantify, involves the complexity of inorganic carbon speciation, and as shown in this study, likely requires a two-station approach. Here, we developed DIC metabolism models using single- and two-station approaches. We compared metabolism estimates based on simultaneous DO and DIC monitoring in the Upper Clark Fork River (USA), which also allowed us to estimate ecosystem-level photosynthetic and respiratory quotients (PQE and RQE). We observed that metabolism estimates from DIC varied more between single- and two-station approaches than estimates from DO. Due to carbonate buffering, CO2 is slower to equilibrate with the atmosphere compared to DO, likely incorporating a longer distance of upstream heterogeneity. Reach-averaged PQE ranged from 1.5 to 2.0, while RQE ranged from 0.8 to 1.5. Gross primary production from DO was larger than that from DIC, as was net ecosystem production by 100 mmol m 2 d 1 . The river was autotrophic based on DO but heterotrophic based on DIC, complicating our understanding of how metabolism regulated CO2 production. We suggest future studies simultaneously model metabolism from DO and DIC to understand carbon processing in rivers.

Abstract Image

从溶解氧和无机碳估算出的新陈代谢差异:对河流碳循环的影响
河流能有效地收集、处理和运输源自陆地的碳。河流生态系统的新陈代谢是处理碳的主要机制。几十年来,溶解氧(DO)的昼夜循环一直被用来推断河流生态系统的新陈代谢率,这些新陈代谢率通常被用来预测二氧化碳(CO2)的新陈代谢,其假定化学计量的不确定性为 4 倍。在此,我们使用单站和双站方法建立了 DIC 代谢模型。我们比较了克拉克福克河上游(美国)基于溶解氧和 DIC 同步监测的代谢估算值,这也使我们能够估算生态系统水平的光合商数和呼吸商数(PQE 和 RQE)。我们观察到,与溶解氧估算值相比,DIC 估算值在单站和双站方法之间的差异更大。由于碳酸盐的缓冲作用,与溶解氧相比,二氧化碳与大气平衡的速度较慢,这可能与上游异质性的距离较长有关。到达平均 PQE 在 1.5 到 2.0 之间,而 RQE 在 0.8 到 1.5 之间。溶解氧产生的总初级生产量大于 DIC 产生的总初级生产量,生态系统的净生产量也大于......。根据溶解氧计算,河流是自养型的,但根据 DIC 计算,河流是异养型的,这使我们对新陈代谢如何调节 CO2 产量的理解更加复杂。我们建议未来的研究同时模拟溶解氧和 DIC 的新陈代谢,以了解河流的碳处理过程。
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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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