资源环境科技发展态势分析平台

Nitrous oxide (N2O) is a potent greenhouse gas with an estimated 10% of anthropogenic N2O coming from the hyporheic zone of streams and rivers. However, difficulty in making accurate fine-scale field measurements has prevented detailed understanding of the processes of N2O production and emission at the bedform and flowline scales. Using large-scale, replicated flume experiments that employed high-density chemical concentration measurements, we have been able to refine the current conceptualization of N2O production, consumption, and emission from the hyporheic zone. We present a predictive model based on a Damkohler-type transformation ((tau) over tilde) in which the hyporheic residence times (tau) along the flowlines are multiplied by the dissolved oxygen consumption rate constants for those flowlines. This model can identify which bedforms have the potential to produce and emit N2O, as well as the portion and location from which those emissions may occur. Our results indicate that flowlines with (tau) over tilde (up) ((tau) over tilde as the flowline returns to the surface flow) values between 0.54 and 4.4 are likely to produce and emit N2O. Flowlines with (tau) over tilde (up) values of less than 0.54 will have the same N2O as the surface water and those with values greater than 4.4 will likely sink N2O (reference conditions: 17C, surface dissolved oxygen 8.5mg/L). N2O production peaks approximately at (tau) over tilde =1.8. A cumulative density function of (tau) over tilde (up) values for all flowlines in a bedform (or multiple bedforms) can be used to estimate the portion of flowlines, and in turn the portion of the streambed, with the potential to emit N2O.