Geochemical Processes Controlling Ionic Composition of Water in the Catchments of Lakes Saana and Saanalampi in the Kilpisjärvi Area of North Scandinavia
Round 1
Reviewer 1 Report
All comments and recommendations are in the attached file. I'm pasting them in here too:
General remarks
The stated aim of this paper is the determine whether (and where?) pyrite is present in the study
area and if so, its impact on weathering processes and the local environment. They quite rightly
conclude that there is chemical heterogeneity in this catchment with sulphuric acid weathering only
important in the west. The Piper diagram of Figure 8 shows a clear difference between streams and
porewaters on the eastern and western sides of Lake Saana which seems convincing to me. I think
this study deserves to be published but the manuscript needs improvement.
Major points:
With respect to pyrite, the authors present XRD data with unexplained peaks but do not attempt to
discuss these in the light of known pyrite peaks. If none of those peaks are pyrite then they should
explain this. No XRD data are presented for the claystone which is 9% S by weight. Possible
pyrite signals in the XRD data deserve more consideration.
It would be useful to have some sort of conceptual diagram showing what flow paths the authors
consider to be most likely and where they think the pyrite, dolomite and silicate minerals might be
weathered along those flowpaths. For example, has water flowed from the top of Mt Saana through
the quaternary sediments, quartzite, dolomite and claystone down to the western sampling points,
implying high permeability or at least sufficient fractures in these rocks? Or does it flow along
relatively impermeable quartzite to streams, only interacting with the exposed dolomite and
claystone on its way downslope or with dolomite and claystone rubble at the foot of the slope? The
paragraphs in section 4.4 (lines 274 through 294) are rather confusing and a diagram might make
things clear.
The abstract ends with a statement about ecological heterogeneity but this is not discussed in the
paper except to say that existing studies are not detailed enough to draw conclusions. It would be
good to either say a bit more about this or to leave it out entirely. A simple vegetation survey (eg
with quadrats near the sampling points) could have been helpful here.
Specific remarks
Soils: Is it safe to assume that the soils are basically Quaternary sediments which have undergone
only slight pedogenesis? What are these sediments, glacial till? Is it derived from the Archean or
Caledonian rocks, or from other rocks and transported from further afield? What is the depth to
bedrock? Is this known for the sampling points?
Figure 1b: It would be good to have a vertical scale here.
Introduction line 120: where is the northern inflow on Figure 1b? I don't really understand what is
meant by the northern inflow “forming a well-defined bed”; please clarify.
Lake samples, runoff and Sampling point 4: These don’t appear in any of the tables. I suppose
that Table 2 is subsurface (pore) water and Table 3 is streamwater, so lake/runoff/outlet samples do
not fit those categories (perhaps it would be better to have a single table with all the data).
However, it would be nice to know a bit more about the lake/runoff samples. Were the lake samples
taken from the surface of the lake or at some depth; how deep is the lake and is it stratified? How is
runoff defined? Sometimes this refers to overland runoff and sometimes to streamwater leaving a
catchment. Is runoff simply streamwater from sampling point 4?Piezometer tubes: Piezometers are used for measuring pressures... here, they’ve been used to
sample the pore water. This is a bit confusing.
Surface samples or waters are referred to throughout the text; should these all be subsurface?
Units: It may be personal preference on my part but I really prefer molar units for solutes, which
make it easier to understand the weathering. For example, the dolomite dissolution does not appear
to be congruent (ie Ca and Mg are not released stoichiometrically) . It would be nice to see that in
the figures and tables without having to mentally convert from milligrams, seeing as Ca and Mg
have different atomic masses. There may be contributions from the Mg-chlorite and/or oligoclase
(ie silicate weathering) of course and it might be necessary to look at the strontium isotopes, but
perhaps the authors plan another paper about that.
Evaporative concentration is suggested as the reason for increased chloride concentrations
(section 4.3 line 238) while low sulphate concentrations may be related to anaerobic microbial
oxidation of organic matter. It is not clear to me that evaporative concentration would create anoxic
conditions; surely there would be greater air-filled porosity following evaporation? Has sulphate
been maintained below a threshold by microbial activity regardless of evaporation?
Gypsum karst is referred to in section 4.2 line 200. Where is this gypsum karst, which isn’t shown
in Figure 1? Or is this a general statement about gypsum?
Table 1: please put “weight %” instead of just “%”. Although “weight %” is clearly stated in the
text, it is always good to make it clear in the table as not all readers will read from start to finish.
Also, “rock type” seems an odd column heading when most of the entries are “soil”. Perhaps these
entries ought to read “Quaternary sediments”, or the heading could be “sample type”. Why does the
deepest sample from sampling point 3 have very different chemistry? Does the AR stand for
Archean?
Figure 4 is not well explained; what are the two traces on each panel? The panels themselves are
not explained in the caption; if (a) is the dolomite sample and (b) is soil sample 1 please say so. Of
greater concern are the unexplained peaks of panel (b). Pyrite has several peaks between 30 and 50;
could any of these unexplained peaks be pyrite? As the point of the paper is to determine whether
pyrite occurs in this catchment it would be good to know whether pyrite shows up in the XRD.
Figure 8: Does “hydrocarbon” refer to the carbonate system (carbonic acid H 2 CO 3 , bicarbonate and
carbonate ions) or just bicarbonate? If it refers to the carbonate system, was the partial pressure of
carbon dioxide gas measured (should be well above ambient in the pore waters) followed by the
various equilibria assuming either open or closed system? Alternatively, was bicarbonate (with or
without carbonate ion) assumed to just charge-balance the major ions given no nitrogen species or
organic acids?
Some minor linguistic and typographical errors:
Abstract line 25: “rate” needs an “s” in the penultimate sentence, ie “ ...chemical weathering rates
of the rocks...
Introduction line 67: change “on” to “in”: “... the presence of pyrite in the ...”
Section 2 line 83: “The area situates in the altitude of...” is peculiar. Could say “The study area has
an altitude of ...” or something like that.Table 1: “Basaltic dyke AR”
Figure 4: Various mineral misspellings: amphibole, oligoclase ...
Section 4.2 line 205: “become controlled” should be “becomes controlled”
Table 3 headings: El.cond. instead of El;cond;
Section 4.3 line 224: Change to “... have been detected, a clear relationship between ...”
Caption Figure 8 line 233: change to “ ... presented in the Supplementary Information.”
Section 4.4 line 264: Get rid of extra comma: “Although feeze-thaw cycles ...”
Section 4.4 line 292: “... are well represented in the catchment.”
Conclusion line 342: “... stayed times lower than ...” I don’t know what this means...
Conclusion line 345: need a space (streamscould): “... streams could ...”
Comments for author File: 
Comments.pdf
Author Response
Dear Editor and Reviewers,
We have modified the manuscript to accommodate the reviewer comments which will help to improve the scientific rationale of this paper. Please find below our responses to the questions and comments that arose from the reviews.
Reviewer 1.
1. With respect to pyrite, the authors present XRD data with unexplained peaks but do not attempt to discuss these in the light of known pyrite peaks. If none of those peaks are pyrite then they should explain this.
The peaks between 30 and 50 belong to oligoclase. Percentage of minerals has been added to the Figure 4 and Supplementary A.
2. No XRD data are presented for the claystone which is 9% S by weight. Possible pyrite signals in the XRD data deserve more consideration.
Correction. The sulphur percentage of claystone is only 0.09. An unfortunate typo has occurred in the text (0.9%, line 161). The co-author who collected the rock samples is on vacation and has not answered my question regarding the XRF analyses. They have probably not been done, otherwise I would have added them.
3. It would be useful to have some sort of conceptual diagram showing what flow paths the authors consider to be most likely and where they think the pyrite, dolomite and silicate minerals might be weathered along those flowpaths. For example, has water flowed from the top of Mt Saana through the quaternary sediments, quartzite, dolomite and claystone down to the western sampling points, implying high permeability or at least sufficient fractures in these rocks? Or does it flow along relatively impermeable quartzite to streams, only interacting with the exposed dolomite and claystone on its way downslope or with dolomite and claystone rubble at the foot of the slope? The paragraphs in section 4.4 (lines 274 through 294) are rather confusing and a diagram might make things clear.
The conceptual model about geochemical processes and flow paths has been added as Figure 12.
4. The abstract ends with a statement about ecological heterogeneity but this is not discussed in the paper except to say that existing studies are not detailed enough to draw conclusions. It would be good to either say a bit more about this or to leave it out entirely. A simple vegetation survey (eg. with quadrats near the sampling points) could have been helpful here.
The statement about ecological heterogeneity has been removed from the abstract.
Specific remarks
5. Soils: Is it safe to assume that the soils are basically Quaternary sediments which have undergone only slight pedogenesis? What are these sediments, glacial till? Is it derived from the Archean or Caledonian rocks, or from other rocks and transported from further afield? What is the depth to bedrock? Is this known for the sampling points?
The surface is covered with boulders and we could drill holes deeper than half a metre only in 10% of cases. It was difficult to estimate the precise transition line. We were able to drill into the depth of 2 metres only once (sampling point 8), and then we definitely reached bedrock. The Quaternary layer there appears to be just over a metre thick. We could not determine the exact origin of the sediments. The lower part of the Quaternary sediments seemed to be local claystone mixed with arkoze boulders. Lake sediments were also found, which suggests that Lake Saana has been much larger than it currently is. The humus layer is about 1 to 2 cm thick, but in the southern wetland the layer can exceed 10 cm (sampling point 3), most likely carried there from the slopes. All these are merely visual observations, not in-depth analysis.
6. Figure 1b: It would be good to have a vertical scale here.
The scale has been added.
7. Introduction line 120: where is the northern inflow on Figure 1b? I don't really understand what is meant by the northern inflow “forming a well-defined bed”; please clarify.
The sentence is misleading. Northern inflow and southern outflow are both marked with arrows in Figure 1a. Mostly local streams are shallow (up to 0.1 m deep) and wide (0.1 to 1 m) depending on the slope. Lake Saana’s outflow and inflow form well-defined beds with the depth of 0.4 to 1 m. The corresponding remarks have been added to the text.
8. Lake samples, runoff and Sampling point 4: These don’t appear in any of the tables. I suppose that Table 2 is subsurface (pore) water and Table 3 is streamwater, so lake/runoff/outlet samples do not fit those categories (perhaps it would be better to have a single table with all the data). However, it would be nice to know a bit more about the lake/runoff samples. Were the lake samples taken from the surface of the lake or at some depth; how deep is the lake and is it stratified? How is runoff defined? Sometimes this refers to overland runoff and sometimes to streamwater leaving a catchment. Is runoff simply streamwater from sampling point 4?
Results of chemical analyses of lake water from different depths and that of runoff (sampling point 4) have been presented in the Supplementary file. The lake’s depth (24 m) is mentioned in the description of the catchment (Line 114). Lake samples were taken in late spring when the lake was still under ice cover and no wind mixing occurred.
9. Piezometer tubes: Piezometers are used for measuring pressures… here, they’ve been used to sample the pore water. This is a bit confusing.
The note has been taken into account and the corresponding changes to the text have been made.
10. Surface samples or waters are referred to throughout the text; should these all be subsurface?
I have corrected all of them to “subsurface” or “subsurface water”.
11. Units: It may be personal preference on my part but I really prefer molar units for solutes, which make it easier to understand the weathering. For example, the dolomite dissolution does not appear to be congruent (ie Ca and Mg are not released stoichiometrically). It would be nice to see that in the figures and tables without having to mentally convert from milligrams, seeing as Ca and Mg have different atomic masses. There may be contributions from the Mg-chlorite and/or oligoclase (ie silicate weathering) of course and it might be necessary to look at the strontium isotopes, but perhaps the authors plan another paper about that.
I had the same dilemma about units. Finally, however, I decided to use mg/L because this is how the lab presented its results. Since other reviewers did not mention the problem, I’ve left it as it was, in mg/L.
12. Evaporative concentration is suggested as the reason for increased chloride concentrations (section 4.3 line 238) while low sulphate concentrations may be related to anaerobic microbial oxidation of organic matter. It is not clear to me that evaporative concentration would create anoxic conditions; surely there would be greater air-filled porosity following evaporation? Has sulphate been maintained below a threshold by microbial activity regardless of evaporation?
No. Our idea was that Cl, Ca etc. contents have increased due to evaporative concentration. Only SO4 content has remained low, the explanation of which could be that SO4 is degraded by bacteria. The sulphate-reducing bacteria are also active, although not the dominating type, in aerobic conditions.
13. Gypsum karst is referred to in section 4.2 line 200. Where is this gypsum karst, which isn’t shown in Figure 1? Or is this a general statement about gypsum?
It is a general statement, supplied with a reference [45].
14. Table 1: please put “weight %” instead of just “%”. Although “weight %” is clearly stated in the text, it is always good to make it clear in the table as not all readers will read from start to finish.
Accepted.
15. Also, “rock type” seems an odd column heading when most of the entries are “soil”. Perhaps these entries ought to read “Quaternary sediments”, or the heading could be “sample type”.
“Rock type” is replaced with “Sample type” and “Soil” with “Subsurface” to align with the text.
16. Why does the deepest sample from sampling point 3 have very different chemistry?
I have had the same question. All subsurface samples have good correlation between LOI and sulphur and I have interpreted it as bio-sulphur. The LOI and sulphur contents in this sample are the highest. Perhaps that sample includes a bigger amount of some buried organic material (lake sediments?).
17. Does the AR stand for Archean?
Yes. But I’ve removed the abbreviation from the table.
18. Figure 4 is not well explained; what are the two traces on each panel? The panels themselves are not explained in the caption; if (a) is the dolomite sample and (b) is soil sample 1 please say so. Of greater concern are the unexplained peaks of panel (b). Pyrite has several peaks between 30 and 50; could any of these unexplained peaks be pyrite? As the point of the paper is to determine whether pyrite occurs in this catchment it would be good to know whether pyrite shows up in the XRD.
The figure 4a is carbonate and figure 4b is subsurface sample 1 (Table 1). The legend of the drawing has been corrected. The peaks between 30 and 50 belong to oligoclase. Percentage of minerals has been added to the Figure 4 and Supplementary A.
19. Figure 8: Does “hydrocarbon” refer to the carbonate system (carbonic acid H2CO3, bicarbonate and carbonate ions) or just bicarbonate? If it refers to the carbonate system, was the partial pressure of carbon dioxide gas measured (should be well above ambient in the pore waters) followed by the various equilibria assuming either open or closed system? Alternatively, was bicarbonate (with or without carbonate ion) assumed to just charge-balance the major ions given no nitrogen species or organic acids?
Hydrocarbon means bicarbonate. Corresponding correction has been made to the legend of the figure. NO3 and NH4 were also measured; both were close to the detection limit (0.1 mg/L). Organic acids have not been detected.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The manuscript is well organized and clearly written. It was a pleasure to review it.
Below I suggest a few changes in style:
L83: Why is the first part of the sentence given in bold?
L95: I would prefer “large“ instead of “wide”
L123: I suggest: ..Saanalampi has a northern outflow and some southern inflows draining the ….
L126: ...used in this study….
L128: ...Quaternary drill cores at depth of ….
L129: ... subsurface water… Do you mean “groundwater”?
L132: ….contamination of the samples
L 148: …..were pulverized in a ring mill. Was it a steel or agate ring mill?
L: What is the meaning of the second pattern in Fig. 4A and 4b?
L148: ...followed the Cl- concentration….
L197: better…….sulphur containing minerals…
L303; 304: figures and dimensions have to be separated bay a blank
L339-340: better: ….that H2SO4 controls……
L345: ….streams could create….
The manuscript is well organized and clearly written. It was a pleasure to review it.
pemoe
Author Response
Dear Editor and Reviewers,
We have modified the manuscript to accommodate the reviewer comments which will help to improve the scientific rationale of this paper. Please find below our responses to the questions and comments that arose from the reviews.
Reviewer 2
1. L 148: …..were pulverized in a ring mill. Was it a steel or agate ring mill?
It was a tungsten-cobalt ring mill.
2. L: What is the meaning of the second pattern in Fig. 4A and 4b?
The figure 4a is carbonate and figure 4b is subsurface sample 1 (Table 1). The legend of the drawing has been corrected.
Author Response File: Author Response.docx
Reviewer 3 Report
see attachment
Comments for author File: Comments.pdf
Author Response
Dear Editor and Reviewers,
We have modified the manuscript to accommodate the reviewer comments which will help to improve the scientific rationale of this paper. Please find below our responses to the questions and comments that arose from the reviews.
Author Response File: Author Response.pdf
