Chomicki K M, Schiff S L
Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada.
Sci Total Environ. 2008 Oct 15;404(2-3):236-44. doi: 10.1016/j.scitotenv.2008.04.024. Epub 2008 Jun 6.
Oxygen (O(2)) is required for life in higher organisms, however, processes such as respiration, the oxidation of reduced inorganic species, and the photolytic breakdown of dissolved organic matter (DOM) decrease the O(2) concentrations in aquatic systems. Filtered, inoculated, and sterile samples of stream waters from Ontario, Canada, were incubated in natural sunlight to examine the effects of photolysis of DOM, respiration, and abiotic reactions on O(2) consumption and delta(18)O of dissolved oxygen (delta(18)O-O(2)). Oxygen consumption rates in the light were up to an order of magnitude greater than in the dark, suggesting light-mediated processes controlled O(2) consumption. Rates of O(2) loss were the same for each treatment (i.e. filtered, inoculated, and sterile) indicating that photolysis was the dominant O(2) consuming process over respiration in these incubations. O(2) consumption rates were different between streams, even when normalized to the change in dissolved organic carbon (DOC), signifying that DOM photolability varied among streams. During DOM breakdown to CO(2), the lighter (16)O isotopomer was preferentially consumed. Fractionation factors observed for photolysis, respiration, and abiotic reactions ranged between 0.988 and 0.995, and were similar in both the light and in the dark incubations in all streams. These fractionation factors are not a function of O(2) consumption rates, and are outside the range published for respiration (0.975-0.982). In current models of O(2) and delta(18)O-O(2), photolysis and respiration are not considered separately and the isotopic fractionation during respiration that is measured in the dark is used in the light. In these incubations, DOM degradation and abiotic reactions are important O(2) consuming and delta(18)O-O(2) fractionating processes. Current models of O(2) and delta(18)O-O(2) incorporate photolysis of DOM and other abiotic processes into the respiratory component of O(2) consumption, thereby overestimating respiration and underestimating photosynthesis to respiration ratios. Consequently, photolysis and abiotic reactions should be considered separately, particularly in shallow aquatic systems with high DOC.
高等生物的生命活动需要氧气（O₂），然而，诸如呼吸作用、还原态无机物的氧化以及溶解有机物（DOM）的光解等过程会降低水生系统中的O₂浓度。对来自加拿大安大略省的溪水进行过滤、接种和无菌处理后，置于自然阳光下孵育，以研究DOM光解、呼吸作用和非生物反应对O₂消耗以及溶解氧的δ¹⁸O（δ¹⁸O-O₂）的影响。光照下的O₂消耗速率比黑暗中高出一个数量级，这表明光介导过程控制着O₂消耗。每种处理（即过滤、接种和无菌处理）的O₂损失速率相同，这表明在这些孵育过程中，光解是比呼吸作用更主要的O₂消耗过程。即使将O₂消耗速率归一化到溶解有机碳（DOC）的变化量，不同溪流之间的O₂消耗速率仍存在差异，这表明不同溪流中DOM的光解性各不相同。在DOM分解为CO₂的过程中，较轻的¹⁶O同位素异构体优先被消耗。观察到的光解、呼吸作用和非生物反应的分馏系数在0.988至0.995之间，并且在所有溪流的光照和黑暗孵育中都相似。这些分馏系数不是O₂消耗速率的函数，且超出了已公布的呼吸作用的范围（0.975 - 0.982）。在当前的O₂和δ¹⁸O-O₂模型中，光解和呼吸作用没有被分别考虑，而是将黑暗中测量的呼吸作用期间的同位素分馏用于光照条件下。在这些孵育过程中，DOM降解和非生物反应是重要的O₂消耗和δ¹⁸O-O₂分馏过程。当前的O₂和δ¹⁸O-O₂模型将DOM光解和其他非生物过程纳入O₂消耗的呼吸成分中，从而高估了呼吸作用并低估了光合与呼吸的比率。因此，应分别考虑光解和非生物反应，特别是在DOC含量高的浅水水生系统中。
