Streams in high-elevation tropical ecosystems known as páramos may be significant sources of carbon dioxide (CO₂) to the atmosphere by transforming terrestrial carbon to gaseous CO₂. Studies of these environments are scarce, and estimates of CO₂ fluxes are poorly constrained. In this study, we use two independent methods for measuring gas transfer velocity (k), a critical variable in the estimation of CO₂ evasion and other biogeochemical processes. The first method, kinematic k₆₀₀ (k_600-K), is derived from an empirical relationship between temperature-adjusted k (k₆₀₀) and the physical characteristics of the stream. The second method, measured k₆₀₀ (k_600-M), estimates gas transfer velocity in the stream by in situ measurements of dissolved CO₂ (pCO₂) and CO₂ evasion to the atmosphere, adjusting for temperature. Measurements were collected throughout a 5-week period during the wet season of a peatland-stream transition within a páramo ecosystem located above 4000 m in elevation in northeastern Ecuador. We characterized the spatial heterogeneity of the 250-m reach on five occasions, and both methods showed a wide range of variability in k₆₀₀ at small spatial scales. Values of k_600-K ranged from 7.42 to 330 m/d (mean = 116 ± 95.1 m/d), whereas values of k_600-M ranged from 23.5 to 444 m/d (mean = 121 ± 127 m/d). Temporal variability in k₆₀₀ was driven by increases in stream discharge caused by rain events, whereas spatial variability was driven by channel morphology, including stream width and slope. The two methods were in good agreement (less than 16% difference) at high and medium stream discharge (above 7.0 L/s). However, the two methods considerably differed from one another (up to 73% difference) at low stream discharge (below 7.0 L/s, which represents 60% of the observations collected). Our study provides the first estimates of k₆₀₀ values in a high-elevation tropical catchment across steep environmental gradients and highlights the combined effects of hydrology and stream morphology in co-regulating gas transfer velocities in páramo streams.

中文翻译：

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使用两种独立方法的热带高海拔气流中气体传输速度的时空变化

通过将陆地碳转化为气态 CO _{2 ，}被称为 paramos 的高海拔热带生态系统中的溪流可能是大气中二氧化碳 (CO ₂ ) 的重要来源。对这些环境的研究很少，并且对 CO ₂通量的估计很少受到限制。在这项研究中，我们使用两种独立的方法来测量气体转移速度 ( k )，这是估算 CO ₂逃逸和其他生物地球化学过程的关键变量。第一种方法，运动学k ₆₀₀ ( k _600-K )，源自温度调整后的k ( k ₆₀₀) 和流的物理特性。第二种方法是测量k ₆₀₀ ( k _600-M )，通过原位测量溶解的 CO ₂ (pCO ₂ ) 和 CO ₂逃逸到大气中，并根据温度进行调整，从而估计气流中的气体转移速度。在位于厄瓜多尔东北部海拔 4000 米以上的帕拉莫生态系统内泥炭地-溪流过渡的雨季期间，在整个 5 周期间收集了测量数据。我们五次对 250 米河段的空间异质性进行了表征，两种方法在小空间尺度上都显示出k ₆₀₀的广泛变异性。的值ķ _600-K范围为 7.42 至 330 m/d（平均值 = 116 ± 95.1 m/d），而k _{600-M 的}值范围为 23.5 至 444 m/d（平均值 = 121 ± 127 m/d）。k _{600 的}时间变化是由降雨事件引起的河流流量增加驱动的，而空间变化是由渠道形态驱动的，包括河流宽度和坡度。这两种方法在高中流排放（高于 7.0 L/s）时非常吻合（差异小于 16%）。然而，这两种方法在低流量排放（低于 7.0 L/s，占收集到的观测值的 60%）时彼​​此有很大不同（差异高达 73%）。我们的研究提供了k _{600 的初步}估计 跨越陡峭环境梯度的高海拔热带集水区的价值，并突出了水文和河流形态在共同调节帕拉莫河流中的气体传输速度方面的综合影响。