Spatiotemporal variability of gas transfer velocity in a tropical high‐elevation stream using two independent methods

摘要

Streams in high‐elevation tropical ecosystems known as páramos may be significant sources of carbon dioxide (CO_(2)) to the atmosphere by transforming terrestrial carbon to gaseous CO_(2). Studies of these environments are scarce, and estimates of CO_(2)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 CO_(2)evasion and other biogeochemical processes. The first method, kinematick _(600)(k _(600‐K)), is derived from an empirical relationship between temperature‐adjustedk (k _(600)) and the physical characteristics of the stream. The second method, measuredk _(600)(k _(600‐M)), estimates gas transfer velocity in the stream by in?situ measurements of dissolved CO_(2)(pCO_(2)) and CO_(2)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 ink _(600)at small spatial scales. Values ofk _(600‐K)ranged from 7.42 to 330?m/d (mean?=?116?±?95.1?m/d), whereas values ofk _(600‐M)ranged from 23.5 to 444?m/d (mean?=?121?±?127?m/d). Temporal variability ink _(600)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 ofk _(600)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.