Climate change: temperature and oxygen impacts on the photooxidation of dissolved organic carbon (DOC)

IF 3.261
Ora E. Johannsson , Marcio S. Ferreira , Anne Crémazy , Gudrun De Boeck , Adalberto L. Val , Chris M. Wood
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Abstract

Over the past 20 years, the Amazon has experienced extreme floods, droughts and warmer temperatures due to climate change. Water temperature in the Rio Negro, a major tributary of the Amazon River, reached it highest October value during the 2023 drought. In Lake Tefé, connected to the Rio Solimões (another major tributary of the Amazon river), water temperatures reached 39°C. Increasing temperatures, and associated decreases in oxygen, will plague the Amazon and other regions, altering and accelerating links in the carbon cycle, such as photooxidation of dissolved organic carbon (DOC). We determined the response of DOC photooxidation rate in the Rio Negro (black-water) and Rio Solimões (white-water) to increases in water temperature between 20°C and 40°C and oxygen concentration between 0.01 mg O2.l-1 and 8 mg O2.l-1. The temperature coefficient (Q10) averaged 1.165, indicative of the dominance of diffusive processes, presumably of reactive oxygen species involved in photooxidation. Direct kinetic release of CO2 was 15% to 21% of normoxic CO2 production, and did not respond to temperature. The activation energy (Ea) of photooxidation was 13.14 kJ.mol-1 in the Rio Solimões and14.09 kJ.mol-1 in the Rio Negro. The Eas were not significantly different, suggesting no differences in the cost of photooxidation between the two rivers. They align with UVB Eas. Photooxidative production of CO2 only became oxygen limited between 0.5 mgO2.l-1 – 0.8 mgO2.l-1 (1.2 kPa – 1.9 kPa, 23°C). Thus, near-surface levels of oxygen are unlikely to directly depress CO2 production of DOC as temperatures rise.
气候变化:温度和氧气对溶解有机碳(DOC)光氧化的影响
在过去的20年里,由于气候变化,亚马逊经历了极端的洪水、干旱和气温升高。亚马逊河的主要支流内格罗河的水温在2023年干旱期间达到了10月份的最高水平。在与里约热内卢Solimões(亚马逊河的另一条主要支流)相连的tef湖,水温达到了39°C。气温升高,以及随之而来的氧气减少,将困扰亚马逊河流域和其他地区,改变和加速碳循环的环节,如溶解有机碳(DOC)的光氧化。我们测定了里约热内卢Negro(黑水)和里约热内卢Solimões(白水)中DOC光氧化速率对水温在20°C ~ 40°C之间升高和氧气浓度在0.01 mg O2之间升高的响应。l-1和8毫克o2 -1。温度系数(Q10)平均为1.165,表明扩散过程占主导地位,可能是参与光氧化的活性氧。二氧化碳的直接动力学释放是常压二氧化碳产量的15%至21%,并且不受温度的影响。光氧化反应的活化能为13.14 kJ。mol-1在里约热内卢Solimões和14.09 kJ。摩尔-1在里约热内卢黑人。Eas没有显著差异,这表明两条河流的光氧化成本没有差异。它们与中波紫外线排列。光氧化产生的CO2仅在0.5 mgO2之间成为氧气限制。l-1 - 0.8 mgO2l-1 (1.2 kPa - 1.9 kPa, 23℃)。因此,随着温度的升高,近地表的氧气水平不太可能直接降低DOC的二氧化碳产量。
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CiteScore
4.10
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