Simulated methane emissions from Arctic ponds are highly sensitive to warming
Abstract. We employ a new, process-based model for methane emissions from ponds (MeEP) to investigate the methane-emission response of polygonal-tundra ponds in Northeast Siberia to warming. Small and shallow water bodies such as ponds are vulnerable to warming due to their low thermal inertia compared to larger lakes, and the Arctic is warming at an above-average rate. While ponds are a relevant landscape-scale source of methane under the current climate, the response of pond methane emissions to warming is uncertain. MeEP differentiates between the three main pond types of the polygonal tundra, ice-wedge, polygonal-center, and merged polygonal ponds. The model resolves the three main pathways of methane emissions – diffusion, ebullition, and plant-mediated transport – at the temporal resolution of one hour, thus capturing daily and seasonal variability of the methane emissions. The model was tuned using chamber measurements resolving the three methane pathways. We perform idealized warming experiments, with increases in the mean annual temperature of 2.5, 5, and 7.5 °C on top of a historical simulation. The simulations reveal an overall increase of 1.33 g CH4 year-1 °C-1 per square meter of pond area. Under annual temperatures 5 °C above present temperatures pond methane emissions are more than three times higher than now. Most of this emission increase is due to the additional substrate provided by the increased net productivity of the vascular plants. Furthermore, plant-mediated transport is the dominating pathway of methane emissions in all simulations. We conclude that vascular plants as a substrate source and efficient methane pathway should be included in future pan-Arctic assessments of pond methane emissions.
Zoé Rehder et al.
Status: final response (author comments only)
RC1: 'Comment on bg-2022-240', Anonymous Referee #1, 08 Feb 2023
- AC1: 'Reply on RC1', Zoé Rehder, 11 May 2023
RC2: 'Comment on bg-2022-240', Anonymous Referee #2, 19 Apr 2023
- AC2: 'Reply on RC2', Zoé Rehder, 11 May 2023
Zoé Rehder et al.
Zoé Rehder et al.
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The manuscript by Rehder et al. Employs a process-based model for methane emissions from ponds to investigate who methane emissions from polygonal-tundra ponds will be affected by warming. This is a very important topic, especially now that we know that the Arctic has been warming faster than any other region in the world and that this warming may let to the proliferation of thaw ponds. Although the model seems to be robust, my major concern is the applicability of the model to other sites to be able to extrapolate the findings to other regions. Moreover, what about the representativity of the selected ponds regarding ponds in the Arctic? In my opinion, a new section discussing how to upscale the results would be useful. Also, a sensitivity analyses of the models needs to be added.
Line 1 I suggest starting the abstract with the broad picture, i.e., mentioning that ponds are important sources of CH4 and vulnerable to warming. After that, authots can focus on the objective of your study.
Line 5 I think the abstract contain too many details about the model. That should be placed in the Methods section. Focus on the main characteristics of the model, its novelty, and the main results.
Line 9 Why these warming temperatures were chosen? Explain this later in the methods.
Line 10 Mention here that this increase in warming seems to be linear with temperature.
Line 17 I have missed a first paragraph to contextualize the topic.
Lines 17-23 This paragraph contains some information that should be included in the methods or study site section.
Line 25 A quantification of the importance of ponds as a source of CH4 to the atmosphere needs to be included.
Line 50 Can not also young or recent accumulated C fuel methanogenesis?
Line 54 Add some information about how substrate quality affect CH4 emissions from ponds.
General I would include a brief information about the model at the end of the introduction. Mentioning if there are other models that have been built, or why the MeEP is relevant and its novelty.
Material and Methods
Line 180: there more studies in the area that show that these ponds are important sources of CH4?
Line 184: What does “how compact the shape of the pond is” mean? (line 184)
Line 190 Please, justify why you assume NPP = GPP/2
Figure 3 The graph showns an R2 = 0.54, can the authors suggest with mechanismos could explain the rest of the variance?
Results and discussion