|This is still a potentially publishable manuscript, however there are a few edits that need to be made.|
I would like to heavily encourage the authors to submit a revised manuscript with all the changes highlighted and indicate in the response to reviewers exactly the text changed. Because this was not done, I had to reread the entire manuscript, and thus, perhaps I have found elements that were in the first version, but would have missed if the authors has highlighted their changes more effectively.
The question of what kind of deposition the authors are looking at is better explained in the methods section: I see there the highlighted changes. However, I am still not sure that these aren’t the soluble N and P, instead of total deposition. Because of the methods shown, and the uncertainty about what exactly this deposition is, I would like to encourage the authors to be more clear that they are using wet deposition in both the abstract, introduction and conclusions.
In the response to the reviewers, the authors indicate that they are very interested in ecological impacts in managed forests, which is really interesting and important and should be added to the introduction, and more so to the results and conclusions. If they are interested in ecological impacts, aren’t they more interested in N:P ratios in the deposition? Following the ideas of Brahney et al., 2016, shouldn’t they look at how N:P ratios in vegetation relate to the deposition ? The P deposition is much more effective (14x), because less P is required. How does that change the conclusions of this study?
“Based on measurements of P content in various fuels and estimates of the P partitioning during combustion processes, a recent assessment indicates that anthropogenic sources, such as combustion-related emissions, can contribute to over 50% of the global atmospheric P and make a substantial contribution to global P deposition (Wang et al., 2015).” This is not correct. They get this large number by ignoring size differentiation between their model (<20um) and locally produced primary biogenic aerosols, and assuming that deposition in forests generated by locally produced biogenic aerosols (in Tipping et al., 2013) comes from combustion instead. Using different assumptions, Brahney et al., 2015 shows that one can match the Tipping et al., 2013 data, as well as other data constraining the size of the combustion sources (as done in Mahowald et al., 2008, but not done in Wang et al., 2015). Please rewrite to “Based on assumptions of the P partitioning during combustion processes and local deposition, a recent assessment hypothesizes that anthropogenic sources, such as combustion-related emissions, can contribute to over 50% of the global atmospheric P budget (Wang et al., 2015), although this result is very sensitive to assumptions about size distribution (Brahney et al., 2016).”
“Anthropogenic sources have been traditionally thought to make only a small contribution to P deposition (Okin et al., 2004; Mahowald et al., 2008). In contrast, our results emphasize that anthropogenic sources near large cities can have significant impacts on the spatial patterns of regional P deposition. The urban hotpot of P deposition might be derived from intensive combustion-related emissions near urban areas (Wang et al., 2015) and a short-distance transfer of P-containing aerosols from P-rich farmland soils (Anderson et al., 2006).” Again, as in the first version, the Mahowald et al., 2008 study also has hotspots close to cities, so this it is not correct that you need huge P sources from combustion to get this result. Also, you get maximum values close to the arid regions. Please be more clear on this. I would suggest something like: “Anthropogenic sources have been traditionally thought to make only a small contribution to P deposition (Okin et al., 2004; Mahowald et al., 2008), and yet can still result in local hotspots of deposition (e.g. Mahowald et la., 2008: Wang et al., 2015) along with P from arid regions, which is consistent with our study. The urban hotpot of P deposition might be derived from intensive combustion-related emissions near urban areas (Wang et al., 2015) and a short-distance transfer of P-containing aerosols from P-rich farmland soils (Anderson et al., 2006).”