Application of environmental tracers for investigation of groundwater mean residence time and aquifer recharge  in fault-influenced hydraulic drop alluvium aquifers

Ma, Bin; Jin, Menggui; Liang, Xing; Li, Jing

doi:https://doi.org/10.5194/hess-23-427-2019

Articles | Volume 23, issue 1

https://doi.org/10.5194/hess-23-427-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/hess-23-427-2019

© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 23, issue 1

Research article

|

24 Jan 2019

Research article |

| 24 Jan 2019

Application of environmental tracers for investigation of groundwater mean residence time and aquifer recharge in fault-influenced hydraulic drop alluvium aquifers

Bin Ma, Menggui Jin, Xing Liang, and Jing Li

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Final revised paper (published on 24 Jan 2019)
Preprint (discussion started on 10 Apr 2018)

Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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- Supplement

RC1: 'Groundwater mean transit times from CFCs and tritium', Anonymous Referee #1, 14 May 2018
- AC1: 'Response to Referee 1-HESS-2018-143', Bin Ma, 25 Aug 2018
RC2: 'review of the manuscript entitled “Groundwater mean transit times, mixing and recharge in faulted-hydraulic drop alluvium aquifers using chlorofluorocarbons (CFCs) and tritium isotopes”', Anonymous Referee #2, 15 May 2018
- AC2: 'Response to Referee 2-HESS-2018-143', Bin Ma, 25 Aug 2018

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (further review by editor and referees) (05 Sep 2018) by Christine Stumpp

AR by Bin Ma on behalf of the Authors (10 Oct 2018) Author's response Manuscript

ED: Referee Nomination & Report Request started (23 Oct 2018) by Christine Stumpp

RR by Anonymous Referee #1 (02 Nov 2018)

RR by Anonymous Referee #2 (22 Nov 2018)

Suggestions for revision or reasons for rejection

The authors have obviously taken great pain to respond to the reviewers’ criticisms constructively. They have failed completely however to address the fundamental issues raised by the reviewers. Changes are numerous and quite substantial, but superficial. Hence, I still stand to my initial assessment that the authors have written a relatively well done case study that however falls completely short of any kind of originality or innovativeness. The manuscript imitates previous works, but even in what the authors have shown of the revised version, it still suffers from its lack of focus. Estimating groundwater residence times from multiple tracers has been done and redone so many times and is not a sufficient reason for a publication in HESS, except if a methodological breakthough of sorts can be presented (this is not at all the case here). Furthermore, the authors are STILL inconsistent in the use they make of the weighting functions, presenting three potential models (EPM, EMM and DM) in the method section, but retaining the piston-flow model for the analysis of the carbon 14 data. If anything, this shows that the authors have not fundamentally modified their initial (erroneous) analysis, although prompted to do so by the reviewers.

Specific comments:

Remark 3: One can always argue that any kind of environmental or hydrological study is “essential” because of human induced pressures, climate change, necessity to provide policy support data, etc… What I meant to say was however much more simply that I do not see anything new or innovative in the manuscript. I still do not. In particular, the authors reproduce the overall shortcomings of many recent publications on multi-tracer groundwater studies, where the multiple tracer measurements are not used to derive one of more consistent parameterised models (see Maloszewski et al., Journal of Hydrology 66, 1983 for a good example), but instead juggle more or less successfully between different estimates of the mean transit time obtained from each tracer, sometimes comparing the results of models assuming incompatible weighting functions.

Remark 4: “The groundwater residence times (ages) often display a wide range due to the recharge under various climate conditions”. This is correct, but only in a very particular case of arid to hyperarid environments having known a wetter period. In temperate climates, the distribution of transit time at the outlet of a groundwater system is due to the differences in length and flow time of the flow tubes contributing to discharge.
“The exponential–piston flow model (EPM) describes aquifer that containing a segment of exponential flow followed by a segment of piston flow. Piston flow assumes that water mixing from different flow lines is minimal and receiving little or no recharge in the confined aquifer, and the exponential flow assume a full mixing of water in the unconfined aquifer and receiving areally distributed recharge”. This description is not correct, and confirms my impression that the authors do not quite know what they are doing. The EPM does not prescribe the order in which the two components are physically arranged (this is explicitely explained in Maloszewski and Zuber, 1983), because mathematically, it makes no difference for the output concentration. And as far as the exponential model is concerned, mixing occurs at the sampling point and is only exactly true for semi-confined aquifers (see Haitjema, Journal of Hydrolog 172, 1995).
“the MRTs with different RTDs were cross‒referenced”. What does that mean ? Comparing the estimated mean transit times really leads nowhere. Either they are close and the authors will claim there is “satisfactory agreement”, or they are not and an entire section of the discussion will be devoted to that. Model choice still is an open research question, so either the authors present a solid argument as to which model they chose, or some kind of methodology allowing to reject some models (as flawed as it is, the method by Plummer et al. is one example of that).
“In our manuscript, the apparent 14C ages estimation was adopted.” I have already criticised this in the first review. “Apparent age” means you are assuming a piston-flow weighting function. This is not consistent with the method section presenting the EPM, the DM and the EMM as potential models describing the transit time distribution of the aquifer.

Remark 50: “We think that combining 3H and CFCs is a good tool to distinguish the
modern precipitation recharge and to indicate the groundwater mixing properties”. I do not quite know what the authors mean by groundwater mixing properties, but the rest of the paragraph is not an answer to my point at all concerning the very limited use of binary mixing diagrams in multi-tracers studies. The authors just equivocate without actually trying to propose a counter argument.

Remark 57: Figure 11 has been kept by the authors, who at the same time have deleted references to “apparent age” from their manuscript, but not from the analysis ! Do they realize that the plots of figure 11,, being calculated using a piston-flow model, show this very “apparent age” they agreed makes no sense ?

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ED: Publish subject to minor revisions (review by editor) (06 Dec 2018) by Christine Stumpp

AR by Svenja Lange on behalf of the Authors (04 Jan 2019) Author's response

ED: Publish subject to technical corrections (07 Jan 2019) by Christine Stumpp

Short summary

Groundwater supplies the most freshwater for industrial and agricultural production and domestic use in the arid northwest of China. This research uses environmental tracers to enhance one's understanding of groundwater, including aquifer recharge sources and groundwater mean residence times in the alluvium aquifers. The results provide valuable implications for groundwater resources regulation and sustainable development and have practical significance for other arid areas.