the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 24 Oct 2025
Proposing Sources for Discrete Groundwater Discharges to Patterned Pools in Three Regional Raised Northern Peat Bogs
Abstract. Raised northern peat bogs are generally assumed to be entirely precipitation-fed (ombrogenous), suggesting they are void of groundwater (minerogenous) inflow from underlying sediments. Patterned pools in raised bogs have often been attributed to surficial flow filling depressions along the peat surface that produces subtle differences in peat pore-water chemistry. However, we present evidence that certain patterned pools may be partially fed by localized upwelling of minerogenous groundwater from underlying glacial sediments in three northern peat bogs of Maine, USA. Underlying permeable glacial deposits, embedded in hydraulically confining glacio-marine clay deposits, were delineated using ground-penetrating radar and transient electromagnetic surveys. Paired point measurements of temperature and specific conductance (SpC) were surveyed around pools, and statistical relationships indicative of groundwater upwelling were established. Uncrewed aerial systems (UAS) thermal infrared (TIR) mapping was conducted, augmented by handheld TIR imaging, to examine characteristic groundwater temperatures in cold and warm seasons across pool surfaces. Surface water samples were acquired to assess the relationship between SpC/temperature signals and elevated iron and manganese concentrations that could be indicative of glacial aquifer sources. The combined datasets present evidence for localized upwelling in pools underlain by glacial structures, and the possibility of minerogenous groundwater contributions. Upwelling through the peat matrix is possibly partially facilitated by macropore, peat pipe’ features that serve as preferential flowpaths of varying lengths to the surface. Such upwelling could drive a positive feedback loop where elevated concentrations of ionic constituents repeatedly dilate the peat matrix and/or terminal electron acceptors enhance anaerobic respiration and microbial activity, accelerating the humification of peat around patterned pools and potentially magnifying carbon loss.
- Preprint
(14081 KB) - Metadata XML
-
Supplement
(11731 KB) - BibTeX
- EndNote
Status: open (extended)
- CC1: 'Comment on egusphere-2025-4567', Giacomo Medici, 31 Oct 2025 reply
-
RC1: 'Comment on egusphere-2025-4567', Eric Rosa, 07 Jan 2026
reply
Review comments on EGUSPHERE-2025-4567 (for Hydrology and Earth System Sciences)
This study focuses on identifying upwelling groundwater fluxes that could feed patterned pools in raised northern peat bogs in Maine, USA. It also considers the potential impact of these fluxes on the development of patterned pools. This topic is scientifically original and relevant to the readership of HESS. The methodological approaches include geophysical measurements (GPR and transient electromagnetic surveys), thermal imaging, in situ measurements of conductivity and temperature, and water sampling for Fe and Mn concentration analysis. These approaches are relevant to answering the research question. Overall, this is original and scientifically relevant work. However, I believe that some improvements are still needed before publication to maximise the manuscript's scientific impact.
General comment 1: I believe more details are needed in section 2 (Material and methods) to better explain the choices for sampling and in situ measurement points:
- It is stated (L213) that specific conductivity and temperature measurements were conducted at a 25 cm depth a few centimeters from the pools perimeter. This choice is likely justified by the enhanced accessibility of the sites close to pool margins. However, it is important to consider the possibility that measurements taken in the immediate vicinity of the pool margins may not be representative of the conditions prevailing towards the centre of the pools, especially at greater depths. Could thermal stratification occur in some pools, with cold water at the bottom and warmer water at the surface?
- A variety of measurements were conducted on different days at multiple sites. It is to be considered whether there has been a change in the temperature of surface water in pools during the period of measurement. To illustrate this point, if measurements are conducted in August, can stable temperatures be expected between the early morning and the afternoon across all measurement points? The potential impact of temporal variability, i.e. variations in surface water temperature during the day of sampling, on the comparisons between different sampling points merits consideration.
- The selection of Fe and Mn as analytical parameters could be expanded upon. Indeed, the hydrogeochemical behaviour of these two chemical elements is very sensitive to Eh-pH conditions and the presence of organic colloids. Consequently, utilising these two elements as tracers of groundwater flows without also considering Eh-pH values and the presence of organic colloids can result in a high degree of uncertainty. The use of other tracers, such as stable isotopes of the water molecule, could facilitate a more precise analysis of the sources of water feeding the pools.
- Here, the focus is set on advective transport but could diffusion from the underlaying inorganic sediments explain part of the spatial variability in pool water conductivity?
General comment 2: Should it be feasible, it would be of interest to present the precise topographic contours for the peatlands under study. Some figures illustrate upgradient and downgradient areas (e.g., Figure 2); however, it is probable that the flow configuration is more intricate than what is visible in the image. The incorporation of topographic contours (e.g., derived from Lidar data) would facilitate enhanced comprehension of the surface flow paths between pools. This would further facilitate the comprehension of the hydraulic head data presented in Figure S16 and the general pattern illustrated in the conceptual model (Figure 10).
General comment 3: The conceptual model provided in Figure 10 is of particular interest. Nevertheless, further information could be pertinent:
- If possible, it would be relevant to provide an estimate of the topographic gradient between the esker and the lagg and between the central part of the peatland and the lagg.
- If the necessary data are available, it would also be relevant to illustrate the hydraulic gradient between the esker and the peatland. Are there data confirming the higher hydraulic heads in eskers near the studied peatlands?
- The available figures (e.g. 6, S7, S9) do not provide unequivocal evidence to determine whether the eskers are solely buried formations or if they are connected to topographically higher recharge areas. Can this be explained in more details or illustrated on a figure?
General comment 4: While the text on the methodological approaches and results is interesting, it can be difficult for readers unfamiliar with the study sites to follow. This is because several methods were used at different times for three sites. To optimise readability, I would suggest adding a summary table of the work carried out at the different sites to the Materials and Methods section. For example, in such a table, the rows could represent the methods and the columns could represent the sites. The information in the cells could provide information such as the number of measurements and the dates of the measurements. Similarly, a table could be added to the results section, summarising the highlights of the results (using a similar table structure).
Some additional specific comments on the manuscript:
L28 : I believe there is a missing apostrophe
L111 + 112 : the expressions “glacial esker” and “glacial till” are used. Please double check if the term “glacial” is really needed. I believe both are, by definition, of glacial origin. The comment applies to the other appearances of these expressions.
L230 (Eq. 2) : I believe this could be an oversimplification. Is the thermal regime of the pools dependent on their size and depth, as well as groundwater fluxes?
Figure 2 : Would it be relevant to apply a topographic correction to the profiles? This also applies to other profiles shown.
L380 (Figure 6) :à I suggest adding the date of measurements in the figure caption.
L441 : Please explain with more details the reported temperatures. Are all zones associated with temperatures below zero frozen?
L618 : Can you please better explain point c)? Are there measurements/results directly representing this?
L634 (+figure 10) : It would be interesting to add information on the image (conceptual model) on how the parameters you have measured (with geophysics, geochemistry and temperature) help for constraining the model.
L677 : Towards the end of the discussion, you would likely have an opportunity to recommend a series of measures to prioritize in future studies in order to test your conceptual model. What would you recommend to future researchers working on this issue? Such recommendations could inform future research.
Figures S5, S6, S8 : I recommend adding a line between both images and adding labels (A for temperature, B for Conductance).
Tables S1, S2, S3, S4, : Please carefully check how many decimals should be kept for the different values in these tables.
Figure S9 : I am having difficulty understanding how the arrow is oriented in relation to the up- and down-gradient areas. Please could you double-check this?
Figure S15 : I recommend revising the text that appears on the images “3D Surface Plot of Hydraulic Gradient...”. I believe the text in the caption should suffice.
Figure S17 : The hydraulic head contours proposed therein appear to be oversimplified.
Final comment:
Overall, I believe this is a very interesting study, scientifically original and of interest to HESS readers. The suggestions presented above are intended to be constructive, and it is hoped that they will be useful to the authors.
Citation: https://doi.org/10.5194/egusphere-2025-4567-RC1
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 192 | 80 | 20 | 292 | 21 | 10 | 11 |
- HTML: 192
- PDF: 80
- XML: 20
- Total: 292
- Supplement: 21
- BibTeX: 10
- EndNote: 11
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1
General comments
Very good research in the field of groundwater hydrology. Please, follow my guidance and the specific comments to fix the minor issues.
Specific comments
Lines 76-78. “Glaciofluvial esker structures have been modelled to exert changes in the vertical movement of peat pore water, attributed to changes in the topography of the mineral sediment along the base of a bog and the hydraulic conductivity (K) contrasts between eskers and lower K peat”. Insert review papers on flow heterogeneities in fluvial and glacial aquifers worldwide:
- Jansson, P., Hock, R., Schneider, T. 2003. The concept of glacier storage: a review. Journal of Hydrology, 282(1-4), 116-129.
- Agbotui, P.Y., Firouzbehi, F., Medici, G. 2025. Review of effective porosity in sandstone aquifers: insights for representation of contaminant transport. Sustainability, 17(14), 6469.
Line 97. Clearly state the general aim of your research at the end of the introduction.
Line 97. Describe the 3 to 4 general objectives of your research by using numbers (e.g., i, ii, and iii).
Lines 99-139. Insert quantitative information on thickness of your sedimentary deposits.
Lines 99-139. Insert quantitative information from cores on proportion of sand, clay and gravel in your sedimentary deposits.
Line 679-690. Expand the conclusion. The general meaning/impact of your hydro-geophysical research is not evident in these lines.
Figures and tables
Figure 2. Location not evident. Please, insert coordinates.
Figures 3 to 5. Distinguish a Figure A and B.
Figure 6. The difference between Figure A and Figure B is not clear.
Figure 10. Insert a spatial scale.
Figure 10. Specify if a vertical exaggeration if present.