Assessment of Water Quality and Soil Salinity in the Agricultural Coastal Plain (Ravenna, North Italy)
, Mauro De Feudis 1,2,*, Gilmo Vianello 1 and Gloria Falsone 1,2Round 1
Reviewer 1 Report
General comments -
The paper shows the spatial distribution of soil salinity and quality, and water salinity/quality over a region of Italy. Furthermore, it aims to shows the changes over a season. I think the paper would need to address a few issues however:
Temporal scale – is one season enough? Need evidence of how this measured season fits with other seasons.
The changes in water salinity of a season is a very interesting story here – less saline in summer from freshwater dilution. In an ideal world would benefit from longer term measuring, or atleast more data on the typicality of the season measured – was 2017/2018 a particularly wet or dry year? The mean precipitation is detailed. Might be worth showing how the 2017/2018 fits here. Is it typical?
The changes in soil over time aren’t very clearly presented
Whilst reading the paper, it was more challenging to take home the temporal comparisons in soils, the way this is presented it’s a nice description of spatial variation of soil properties in a region of Italy, but harder to extract the changes over time from its current presentation format. Below there are suggestions of where this could be improved (e.g. integration of figures)
No attention to soil structural degradation from salts – this is important for saline impacts to soil function and more relevant to leaching rates
This paper does show that soils will differ, and thus may want to be considered in future leaching considerations. But I feel that more detail is specifically needed on how that might manifest? The authors measure Bulk Density – can they link this to leaching rate and infiltration/flushing? There is no real mention of soil structural degradation from salts, which I think really should be considered given that it can have an adverse effect on soil flushing rates, and thus soil vulnerability.
Link to land use
A link to, and description of the typical cropping and/or land use in the area would also be good. E.g. Is knowledge of soil salinity in the sandier soils as relevant if they are natural vegetation? Where are the high value irrigated crops in relation to all of the soil types?
More specific comments -
Fig 1 – difficult to read (even at 100%) with black and white shading. Could this be in colour and higher resolution? Abbreviation CDR needs to be marked on the map
Line 138 - For the water sample collections, what months do you define as spring/summer and autumn/winter? Please state
Fig 5 and 6 – would be easier for the reader if able to compare maps of summer vs winter/ Perhaps all 4 in one figure? Again, Resolution needs to improve greatly (as on all figures)
Line 278 – not quite sure where the 2% threshold of TOC for soil health comes from – please include relevant citation
Line 281 – but some of these are sandy soils anyway, and would struggle to get above 2% OC. I think it is quite bold to claim that soil functions might be ‘compromised’ on these inherently low C soils anyway – there inherent soil function capacity may not be able to be improved at with such intrinsic soil properties.
Line 283 – please elaborate on meaning of vulnerability. Vulnerable to what? Arenosols are much much sandier than the Cambisols, so would expect low C contents regardless.
Line 298 – higher EC may correlate with more fine textured soils, but this may be likely due to higher CEC in these soils as opposed to sands, so not sure it is right to say they are more vulnerable unless you start to bring in soil structural degradation (dispersion) as a discussion point – which I think is missing from this paper, and a revision would benefit from. That is where clay soils may truly be more vulnerable.
Line 306 – this is a really interesting finding of the paper
Line 310 – Is there any evidence to show and cite that this freshwater dilution is happening? Past studies or documents of current practice? Please cite
Line 332 – guarantee may not be the best word to use
Author Response
The paper shows the spatial distribution of soil salinity and quality, and water salinity/quality over a region of Italy. Furthermore, it aims to shows the changes over a season. I think the paper would need to address a few issues however:
Q1) Temporal scale – is one season enough? Need evidence of how this measured season fits with other seasons.
Q2) The changes in water salinity of a season is a very interesting story here – less saline in summer from freshwater dilution. In an ideal world would benefit from longer term measuring, or atleast more data on the typicality of the season measured – was 2017/2018 a particularly wet or dry year? The mean precipitation is detailed. Might be worth showing how the 2017/2018 fits here. Is it typical?
A to Q1&Q2) The precipitation data of monitored summer season, called into the text “irrigation period”, well fits with the mean summer precipitation measured from 1961 to 2018, being 55 mm and 52 mm, respectively. Therefore, in the monitored irrigation period the soil water balance and the consequent plant water needs fit with other summer seasons. In the monitored summer period, the volume of water used for irrigation and salt leaching purposes is thus typical for the studied area. The monitored winter season (i.e., “non-irrigation period”) is instead wetter than the typical winter period (1961-2018), with 90 and 59 mm as mean precipitation respectively. In the monitored winter period, the salt leaching would be thus even enhanced by this “extra” rainfall, further stressing the strong salt retention occurred in the studied Cambisols. In the revised version, we now report the data precipitation of monitored period in M&M section (see LL 163 – 166 of the new version). We further stress the strong salt retention in Cambisols in winter, considering that we monitored a wetter winter period with respect to the typical one (see LL. 418 – 420 of the new version).
Q3) The changes in soil over time aren’t very clearly presented
Q4) Whilst reading the paper, it was more challenging to take home the temporal comparisons in soils, the way this is presented it’s a nice description of spatial variation of soil properties in a region of Italy, but harder to extract the changes over time from its current presentation format. Below there are suggestions of where this could be improved (e.g. integration of figures)
A to Q3&Q4) In the new version of the manuscript the format of the figures that show the temporal variation of soil properties was changed according to Reviewer 1 suggestions (see also A to Q10)
Q5) No attention to soil structural degradation from salts – this is important for saline impacts to soil function and more relevant to leaching rates
Q6) This paper does show that soils will differ, and thus may want to be considered in future leaching considerations. But I feel that more detail is specifically needed on how that might manifest? The authors measure Bulk Density – can they link this to leaching rate and infiltration/flushing? There is no real mention of soil structural degradation from salts, which I think really should be considered given that it can have an adverse effect on soil flushing rates, and thus soil vulnerability.
A to Q5&Q6) In the Introduction section of revised manuscript, we now refer to the structural degradation of soil due to salinization, as effectively it is a great soil issue such as other serious issues related to soil biology (see LL. 30 – 32 of the new version). No specific measurements of features related to soil structure quality (e.g., aggregate stability, porosity and pore size distribution, etc) have been however performed, being our research mainly focused on the effectiveness of the use of extra water for salt leaching and its consequent on leaching of soluble organic matter pools. We measured the bulk density (BD) values, as physical parameter strongly affecting water drainage and related the soil structure. The BD values have not however been monitored in the two seasons, therefore no conclusions about the effect of salt concentration on BD can be inferred. We agree that the poor physical quality of our Cambisols, as detected by high BD values, can negatively affect the soil flushing rates (as already specified at LL. 290-291 in the previous manuscript version) and consequently the salt leaching. We now specified at LL. 405 – 406 of the new version.
Link to land use
Q7) A link to, and description of the typical cropping and/or land use in the area would also be good. E.g. Is knowledge of soil salinity in the sandier soils as relevant if they are natural vegetation? Where are the high value irrigated crops in relation to all of the soil types?
A to Q7) According to Q7 of Reviewer 1 and Q3 of Reviewer 2 more information about the study area were added (see LL 89 – 107 of the new version)
More specific comments -
Q8) Fig 1 – difficult to read (even at 100%) with black and white shading. Could this be in colour and higher resolution? Abbreviation CDR needs to be marked on the map
A to Q8) The resolution of all figures was improved. Moreover, we noticed that in the previous version of the manuscript the images (not the captions) of Figures 1 and 2 were reversed and may be this made confusions to the reviewers. However, this mistake did not interfere with the text of the manuscript. In the new version of the manuscript the Figures 1 and 2 are the right ones.
Q9) Line 138 - For the water sample collections, what months do you define as spring/summer and autumn/winter? Please state
A to Q9) In Material and methods we defined the months of the considered periods (see LL. 163 – 166 of the new version)
Q10) Fig 5 and 6 – would be easier for the reader if able to compare maps of summer vs winter/ Perhaps all 4 in one figure? Again, Resolution needs to improve greatly (as on all figures)
A to Q10) According to Reviewer 1, Figures 5 and 6 were combined (Figure 5 of the new version) and the quality was improved. As a consequence, both the figure caption and the paragraph 3.3 were rewritten (see LL 302 – 321 of the new version)
Q11) Line 278 – not quite sure where the 2% threshold of TOC for soil health comes from – please include relevant citation
A to Q11) We added the citation, thank you (see L. 389 of the new version)
Q12) Line 281 – but some of these are sandy soils anyway, and would struggle to get above 2% OC. I think it is quite bold to claim that soil functions might be ‘compromised’ on these inherently low C soils anyway – there inherent soil function capacity may not be able to be improved at with such intrinsic soil properties.
A to Q12) We partly disagree with the Reviewer 1, because even if very low OC content in sandy soils is often reported, several researches (e.g., Vinther et al., 2006; Li et al., 2007; Hanegraaf et al., 2009) found soil organic carbon concentrations higher than 2 % in cropland sandy soils. In the revised manuscript, as suggested, we now refer to low function capacity of sandy soils in the Discussion section (see LL. 389 – 393 of the new version), further stressing the risk of soil degradation due to leaching of soluble organic matter in Arenosols.
Q13) Line 283 – please elaborate on meaning of vulnerability. Vulnerable to what? Arenosols are much much sandier than the Cambisols, so would expect low C contents regardless.
A to Q13) In the new version of the manuscript (see LL. 393 – 397 of the new version) we referred the term “vulnerability” to soil degradation caused by the low TOC content. Thank you
Q14) Line 298 – higher EC may correlate with more fine textured soils, but this may be likely due to higher CEC in these soils as opposed to sands, so not sure it is right to say they are more vulnerable unless you start to bring in soil structural degradation (dispersion) as a discussion point – which I think is missing from this paper, and a revision would benefit from. That is where clay soils may truly be more vulnerable.
A to Q14) We have not measured the CEC values of our soil samples, but we agree with the Reviewer 1 that in finer soils the CEC is higher than in sandy soils. In any case, because of the value pH (7.5-7.9) and the presence of CaCO3 in all the soils (see Table 3), the BS% and ESP should be similar among soils. We agree that the differences in soil texture, and consequently, all the physical properties related to the particle size distribution, strongly influence the salt leaching. We now stressed it as suggested (see LL. 405 – 406 of the new version; see also A to Q5-Q6).
Line 306 – this is a really interesting finding of the paper
Q15) Line 310 – Is there any evidence to show and cite that this freshwater dilution is happening? Past studies or documents of current practice? Please cite
A to Q15) In Material and Methods (L 153 of the new version) of the new version we added the citation of the web page of Western Romagna Land Reclamation Consortium and Cipolla et al. (2019) that report how the fresh water introduction in the canal networks during the irrigation summer period is one of the services provided every year by the consortium. Furthermore, at LL 85 – 87 of the new version of the manuscript we briefly added the main services provided by the consortium. Thank you
Q16) Line 332 – guarantee may not be the best word to use
A to Q16) We changed into “allow”. Thank you (L 461 of the new version)
Reviewer 2 Report
The present manuscript investigated salt leaching in Arenosols and Cambisols croplands in the coastal area of Ravenna (Italy) due to irrigation. The study focused on interactions between soil type and water quality, the spatial distribution of soil and water salinity, and highlights the seasonal evolution of soil and water salinity. It was clearly shown that - compared to sandy soils - soils with a high clay content can preferentially store salt from the brackish groundwater and can hardly be desalinated with fresh water irrigation.
The manuscript is well written and clearly structured. However, some additional information is needed, mainly to better understand the methodical setup. In addition, the discussion could be improved e.g. by including some explanations about the geostatistical maps and by relating the discussion more clearly to the results.
Abstract
Line 23: „…leaching from soils due to the high irrigation…” – to be more precise: can you specify soil types or soil properties that are most likely responsible for the increase of nutrients in water bodies?
Introduction
Line 55: “… effectiveness of salt leaching and preservation of soil and water resources…” – basically – yes. However, what about fertilizers? How is it possible to ensure salt leaching, but to keep other important ions (e.g. nitrate…) in the soil for plant nutrition? Leaching of fertilizers could also result in salinization of water bodies… is there any information how to balance salt leaching and nutrient supply at the same time?
Materials and Methods
Chapter 2.1: Would it be possible to give a rough overview about the average agricultural use in the investigation area, e.g. crops (or crop rotation), fertilization strategies etc., as this might influence pH, EC, some of the measured ions and other values?
Chapter 2.2, Figure 2: Were Gleysols and Fluvisols excluded from the study? Why? Leaching water from these soils might have also contributed to the water quality in the investigated canals and drains (Figure 3). For example, the Lamone River is quite far away from soil sampling points – how far is the water quality affected by properties of the investigated soil sampling points?
Please specify how many samples (replicates) were taken from each soil type (or soil “unit”) – sampling strategy is not clear. How did you ensure a representative sampling of the different soils?
Results
Is there any information about the composition and quality of the irrigation water available? Would be important to know how far irrigation water ingredients may change the measured soil properties between seasons, and how far the quality of the irrigation water influences the water quality in the canals and drains.
Figure 4: Wherever possible, you should unify the scale of the y-axis to make differences between summer and winter season more pronounced. Otherwise, it should be highlighted that scales are different. Would it be possible to add another statistical evaluation to find differences between summer and winter season (of the same variable at the same site)?
Figures 5, 6, 7: These figures need to be improved. The numbers on the iso-lines are difficult to read and to interpret. I suggest inserting a legend (color scale with the associated units (dS/m?)) and removing the confusing numbers from the maps. Instead, a reference to Figs. 2 and 3 should be made by e.g. drawing the sampling points (and/or the water canals and drains) on the maps. It is currently not clear which area is shown on these maps.
Line 255: “… in waters monitoring point…” – should be “… in water monitoring points…”?
Line 263-264: refer to Figure 6b
Discussion
Generally, to better relate the data to the discussion, it would be helpful to include references to the results (tables and/or figures).
Line 288: replace “which” by “who”
Line 290: “Cambisols” instead of “Cambisoils”
Line 277-293: How is the discussion about TOC related to the topic of the chapter: Seasonal evolution of soil salinity?
Line 292-293: Relation to the previous TOC discussion is unclear: what does “radical growth” mean here?
Chapter 4.2: This chapter is not related to figures 5,6,7: Why not discussing the spatial variability in this chapter?
Conclusion
Why not repeating the idea of using pipe drains to prevent salt rising from brackish groundwater? I think this is a helpful idea to avoid wasting freshwater and to use irrigation more effectively.
Author Response
The present manuscript investigated salt leaching in Arenosols and Cambisols croplands in the coastal area of Ravenna (Italy) due to irrigation. The study focused on interactions between soil type and water quality, the spatial distribution of soil and water salinity, and highlights the seasonal evolution of soil and water salinity. It was clearly shown that - compared to sandy soils - soils with a high clay content can preferentially store salt from the brackish groundwater and can hardly be desalinated with fresh water irrigation.
The manuscript is well written and clearly structured. However, some additional information is needed, mainly to better understand the methodical setup. In addition, the discussion could be improved e.g. by including some explanations about the geostatistical maps and by relating the discussion more clearly to the results.
Abstract
Q1) Line 23: „…leaching from soils due to the high irrigation…” – to be more precise: can you specify soil types or soil properties that are most likely responsible for the increase of nutrients in water bodies?
A to Q1) In the revised manuscript we reformulate the sentence (LL 22 – 24 of the new version). However, we cannot specify the soil types because the nutrients and organic molecules found in the drainage canals are the results of their leaching from different types of soil.
Introduction
Q2) Line 55: “… effectiveness of salt leaching and preservation of soil and water resources…” – basically – yes. However, what about fertilizers? How is it possible to ensure salt leaching, but to keep other important ions (e.g. nitrate…) in the soil for plant nutrition? Leaching of fertilizers could also result in salinization of water bodies… is there any information how to balance salt leaching and nutrient supply at the same time?
A to Q2) We agree with Reviewer 2 that nutrients leaching is an important issue, especially in poor-C soils as the investigated ones. Thus, also in agreement with the Reviewer 2’s suggestion (Q17), in the Discussion section we now stress the use of alternative practises for soil salinization control avoiding leaching (see LL. 466 – 467 of the new version)
Materials and Methods
Q3) Chapter 2.1: Would it be possible to give a rough overview about the average agricultural use in the investigation area, e.g. crops (or crop rotation), fertilization strategies etc., as this might influence pH, EC, some of the measured ions and other values?
A to Q3) According to Q7 of Reviewer 1 and Q3 of Reviewer 2 more information about the study area were added (see LL 89 – 108 of the new version)
Q4) Chapter 2.2, Figure 2: Were Gleysols and Fluvisols excluded from the study? Why? Leaching water from these soils might have also contributed to the water quality in the investigated canals and drains (Figure 3). For example, the Lamone River is quite far away from soil sampling points – how far is the water quality affected by properties of the investigated soil sampling points?
A to Q4) For Gleysols and Fluvisols, we had very few sampling points (please, compare Figs. 1 and 2). For data processing, thus, the most frequent sampled soils have been taken into account as indicated at LL 171 – 173 of the previous version of the manuscript (LL. 222 – 224 of the new version). Although it is interesting to observe how each soil type can influence the water quality, the aim of our study was to give a wide overview about the water quality in a salt affected area and how the irrigation can affect this quality. Further, the nutrients and organic compounds in the drainage canals are the results of their leaching from more than one soil type, as a consequence, it is not possible to identify their source.
Q5) Please specify how many samples (replicates) were taken from each soil type (or soil “unit”) – sampling strategy is not clear. How did you ensure a representative sampling of the different soils?
A to Q5) The soil sampling density was carried out as a function of the land unit sizes and subsequent refilling was performed in the event of soil characteristic changes within the same land unit. Therefore, the sampling strategy was based on a regular grid, allowing to have about one sampling point every 60 ha (50 sampling points/30 km2 surface of investigated area), according to Wibawa et al. (2013). At LL. 156 – 159 of the new version, we now clearly declare the samples density.
Results
Q6) Is there any information about the composition and quality of the irrigation water available? Would be important to know how far irrigation water ingredients may change the measured soil properties between seasons, and how far the quality of the irrigation water influences the water quality in the canals and drains.
A to Q6) As indicated at LL. 113 – 114 of the previous version of the manuscript (LL 151 – 152 of the new one), the irrigation water comes from Reno river. The data from rivers and CDR has been grouped into FW and FWv which indicate freshwater samples from upstream and downstream stations, respectively. In our case the quality of the irrigation water can be observed by the values of FW reported in Figure 4. Of course, from the upstream to downstream stations the water quality worsts, as a consequence, the irrigation water quality is lower close to the downstream stations than close to upstream station, but in this study it is important to highlight that, basically, for the irrigation purposes water with high quality is used (Please, see also A to Reviewer 1’s Q15).
Q7) Figure 4: Wherever possible, you should unify the scale of the y-axis to make differences between summer and winter season more pronounced. Otherwise, it should be highlighted that scales are different. Would it be possible to add another statistical evaluation to find differences between summer and winter season (of the same variable at the same site)?
A to Q7) We agree with Reviewer 2 comment, but we decided do not change the scale of the figures to better show the differences among the water bodies, in particular for the winter period. However, as suggested by Reviewer 2 we modified the Figure caption highlighting the different scales. Since the aim of the paper was to contrast the considered soils and water bodies in each season, we decided do not perform further statistical analysis. However, Table S2 of the supplementary material contains the statistical summary of the water body parameters in the considered seasons by which its somehow possible to perform the comparisons between the two seasons.
Q8) Figures 5, 6, 7: These figures need to be improved. The numbers on the iso-lines are difficult to read and to interpret. I suggest inserting a legend (color scale with the associated units (dS/m?)) and removing the confusing numbers from the maps. Instead, a reference to Figs. 2 and 3 should be made by e.g. drawing the sampling points (and/or the water canals and drains) on the maps. It is currently not clear which area is shown on these maps.
A to Q8) According to Reviewer 1, a new Figure 5 (with higher resolution) was built which includes the Figures 5 and 6 of the old version. In order to evaluate the spatial variability in the study area for soil EC values (or logEC for the water) a variogram was estimated as provisional map. The new Figure 5 showed the variograms obtained from residual values of linear model, for soil (0-30 cm) and water sampling points in winter and summer periods, which do not allow the inclusion of a chromatic scale, but lighter colors means smaller distance among the residual values. Figure 7 of the old version of the manuscript was deleted because of the poor distance between the residual values of the model. As a consequence of this change, we modified both the figure 5 caption and the paragraph 3.3 (LL 302 – 321 of the new version). Although we agree with Reviewer 2 that, in this figure, it could be nice to draw the sampling point and the water bodies, we decided do not follow his/her suggestion because they make the figure more confusing. However, on the Y and X axes are reported the coordinates, in this way the reader can easily understand the area that the Figure is referring to.
Q9) Line 255: “… in waters monitoring point…” – should be “… in water monitoring points…”?
Q10) Line 263-264: refer to Figure 6b
A to Q9 and Q10) The paragraph 3.3 was modified.
Discussion
Q11) Generally, to better relate the data to the discussion, it would be helpful to include references to the results (tables and/or figures).
A to Q11) We now refer to the tables and figures as suggested
Q12) Line 288: replace “which” by “who”
A to Q12) Done, thank you (L 402 of the new version)
Q13) Line 290: “Cambisols” instead of “Cambisoils”
A to Q13) Done, thank you (L 403 of the new version)
Q14) Line 277-293: How is the discussion about TOC related to the topic of the chapter : Seasonal evolution of soil salinity?
Q15) Line 292-293: Relation to the previous TOC discussion is unclear: what does “radical growth” mean here?
A to Q14-Q15) To better relate the TOC discussion to the topic of the chapter we changed the title of the chapter which, in the new version, is “Organic C concentration and seasonal evolution of soil salinity”. Furthermore, the beginning part of the TOC discussion section was slightly modified to better relate TOC both to the issue of salt-affected soils and to the aims of the paper. (LL 386 – 387 of the new version). Radical growth means the growth of the plant root system, therefore to clarify this part we replaced “radical” with “root” (L 406 of the new version). Thank you.
Q16) Chapter 4.2: This chapter is not related to figures 5,6,7: Why not discussing the spatial variability in this chapter?
A to Q16) According to Reviewer 1, we combined Figs 5 and 6, however in order to better relate the data discussion to the spatial variability of water EC we referred to the new Fig 5 (see LL. 426 – 427 of the new version).
Conclusion
Q17) Why not repeating the idea of using pipe drains to prevent salt rising from brackish groundwater? I think this is a helpful idea to avoid wasting freshwater and to use irrigation more effectively.
A to Q17) We modified the conclusion according to Reviewer 2, thank you. (LL 476 – 477 of the new version)
References
Cipolla, S.S., Maglionico, M., Masina, M., Lamberti, A., Daprà, I., 2019. Real time monitoring of water quality in an agricultural area with salinity problems. Environmental Engineering and Management Journal 18, 2229–2240.
Hanegraaf, M.C., Hoffland, E., Kuikman, P.J., Brussaard, L., 2009. Trends in soil organic matter contents in Dutch grasslands and maize fields on sandy soils. European Journal of Soil Science 60, 213 – 222.
Li, X., Rengel, Z., Mapfumo, E., Singh, B., 2007. Increase in pH stimulates mineralization of ‘native’ organic carbon and nitrogen in naturally salt-affected sandy soils. Plant and Soil 290, 269 – 282.
Vinther, F.P., Hansen, E.M., Eriksen, J., 2006. Leaching of soil organic carbon and nitrogen in sandy soils after cultivating grass-clover swards. Biology and Fertility of Soils 43, 12 – 19.
Western Romagna Land Reclamation Consortium. Available online: https://www.romagnaoccidentale.it/#
Round 2
Reviewer 1 Report
Thanks for making the revisions and addressing the comments raised
