Changes in Surface Water Quality of the El Salvador River in La Joya de los Sachas, Ecuadorian Amazon Region

Round 1

Reviewer 1 Report

I think that the manuscript should be revised, the discussion part need more attention and can be improved, finally, I recommend the rejection of this publication.

Author Response

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Reviewer 2 Report

Review Report

·       Journal: Water (ISSN 2073-4441)

·       Manuscript ID: water-2935658

·       Type: Article

·       Title: Changes in surface water quality of the El Salvador River in La Joya de los Sachas, Ecuadorian Amazon Region

·       Authors: Tannia Vargas-Tierras , Mirian Jimenez-Gutierrez , Sandra Pastrano , Gino Chávez , Vanessa Morales , María Morales , Fernando Paredes-Arcos , and Wilson Vasquez

·       Section: Water Quality and Contamination

·       Special Issue: Assessment of Water Quality and Pollutant Behavior

A)   General Comments:

The authors examine the water pollution problem in the Ecuadorian Amazon that is mainly due to the lack of sewage infrastructure, wastewater treatment plants in urban and rural areas, and itensive agricultural and livestock activities. Information about the water quality is fundamental due to its dynamic nature caused by various activities in this sensitive area. In their paper, the water quality status of the El Salvador River was evaluated and compared with the current standards of the Ministry of the Environment, Water, and Ecological Transition in Ecuador and also with Decree No. 115/2003 on water quality and water pollution management. Within the scope of this study, the water quality index was determined for 7 (seven) samples taken from the selected region (here, the authors could very briefly mention how/with which tool they determine this index). Random sampling was conducted at seven different locations along the river. The results of this study showed that the water quality is currently uite good, with a contamination index in the range of 84-87. Upon comparison of the measurement results with the water quality standards, it can be inferred that all the water quality parameters complied with the given standards which means that the water can be used for recreational purposes. However, since it is used for agricultural activities (irrigation of agricultural land), it was also compared with Table II, Table III and Table IV (here, the authors refer to some Tables called I-II-III-IV, but do not write what these Tables specifically show, which information they give about the water that is examined and to be used in agricultural activities). The authors indicate here some respective nitrate concentrations, namely 20, 13 and > 30 mg/Lwhich are exceeeding the associated water quality standards applied to water that is going to be used for agricultural activities.

Finally, it can be deduced that the presence of this molecule (?they probably mean nitrate ions) is exported by surface runoff to the river from the surrounding crops (this final sentence of the Abstract / Summary would need revision, since it is not clear what is meant with “this molecule” (nitrate ions?).

The Abstract should give a brief and very clear summary of the study. From the Abstract the main ideas / results, but also tools used as well as the aim & sope of the study should be easily understood. However, the authors give some details, mention specific reference tables from water quality (irrigation) standards, but do not describe in this section what they do in their own work  by making use of these tables. Was the scope of this paper measuring some parameters in the river and calculating water quality indexes for these river water samples?

The discussion about the water quality parameter values comes too short and is typical/expected/not surprising for the studied water samples.

Some specific comments are listed below with a special focus on the Results & Discussion as well as Conclusions (& Recommendations) Sections.

B)   Specific Comments:

·       Introduction:

Until Line 49 of this section, the content is very general, some rather basic information about sources and causes of water contamination / pollution are given. In fact, the Ecuadorian Amazon Region is a very rich ecosystem providing a multitude of precious food products. Tourism activities are also mentioned and contribute to the water quality/pollution discharge problem. At the same time, it faces some serious water pollution problems, that have been mentioned together with its reasons. However, interesting would be to give also some quantitative information in this section about the numerical amount (flowrates) of water used for different plants and crops, the number of water and wastewater treatment plants, their type and capacity. This information would be quite useful to the reader and to understand the prevailing situation of the region under study.

In the final part (end of paragraph of this section) it it important to indicate the aim and scope (which tools were used to evaluate the water quality of that region) of the present study.

·       Materials and Methods:

The authors measure some water quality parameters they us efor rive water examination andevaluation. The results are compared with numbers in the related legislations.

-BOD – BOD₅ = 5th day or 5-day biochemical oxygen demand.

-Table 1: Only very few parameters were measured to determine the water quality index.

What about water quality parameters such as total/dissolved organic carbon (TOC/DOC), alkalinity, phosphate, sulfate and color? Some major parameters are missing.

-What are the parameters “SDT” and “DBO5” standing for? TDS = Total Dissolved solids (in mg/L) and BOD₅ (5-day biochemical oxygen demans (in mgO2/L). Please correct.

-Tables 1 & 2: Could be given as supplementary data, in the “Appendix” Section of the paper. These tables are provided as general/reference information. It is not really necessary to give them in the man text.

·       Results:

-What is the unit of conductivity (Line 210)?

·       Discussion:

-There is a problem with the units of the measured parameters. Nitrates are in mg/L units, what is correct, but conductivity must be in mS/cm or microS/cm units. Do the authors mean total dissolved solids (TDS); the TDS unit is mg/L? This is important and should be clarified – what is meant.

-Nitrogen concentrations and rate limiting factors for euthrophication: Typically, P (phosphorus, phosphate anions) is rate limiting among N and P in rivers and lakes. Was phosphate-P measured in samples? Please explain/give more information

-Line 275: Total soluble solids = Total dissolved solids = TDS, not TSS (= total suspendend solids). TSS (total suspended solids) is related to turbidity. The relationships between different parameters are well-known. The authors may clarify the names, units, symbols and relationships between these parameters.

-From the next paragraphs it is evident that according to the measurements, the water quality parameters are still good (their concentration is in the normal range) or at least acceptable/tolerable. This could be attributable to the fact that the strong and diverse ecosystem of the sample region is yet capable of absorbing the examined pollution indicators. The only concern might be the high nitrate and dissolved solids concentrations of the water samples. These should be considered as “alarming” and some precautions should be taken so that their values and also those of the other parameters are not increasing to problematic levels.

-In the Discussion and Conclusion Sections, it is expected that the authors propose some water quality managemement program or strategy to control the high (increasing) nitrate concentrations and salinity (also measured as the conductivity and solids parameter) considering the region’s situation in terms of climatic conditions, water flowrate, activities types in that area, as well as other environmental/social/technical/economical factors.

·       Conclusions:

In the Conclusions Section, the authors directly give the major results of their study regarding the water quality of the El Salvador River. The water quality index of the El Salvador Riverwas also calculated as we know from the summary and the main text of the paper. This index indicated that the studied water could safely be used for recreational activities since the regions has a good water quality index; however, the nitrate concentration in the river exceeded the values determined in the regulations of the reform book VI of the unified text of Secondary Legislation of the Ecuadorian Environment Ministry Ministerial Agreement 097-A and Decree No. 115/2003, Class III. “Considering these facts advisable to carry out periodic sampling to compare the behavior of this molecule over time”(similar phrase with the Abstract). Finally, the authors point out that the intensive agricultural and livestock activities around the river are the major reason of the high the nitrate concentration that could increase over time and become a potential risk to human health in most of the communities of Tres de Noviembre, considering that children are more vulnerable than adults to the carcinogenic effects caused by high nitrate levels in water.

The Conclusion Section looks very similar to the “Abstract” (Summary) Section (in particular the first parts and that one related to nitrate), giving practically the same content and information about the water quality results. The authors could suggest precautions to be taken to control excessive nitrate concentrations by proper management of point/non-points sources, they could give further recommendations / suggestions to improve the river water quality that could be safely used for agricultural irrigation. In this section, some suggestions and recommendations for future work are expected.

Comments for author File: Comments.pdf

The Quality of English is fine. However, there are some parameters that should be translated to English (probably indicated in another/local language)

Author Response

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Reviewer 3 Report

This work analyzes the surface water quality status of the El Salvador River in the Ecuadorian Amazon Region. The analysis is carried out by estimating the Water Quality Index already used for these purposes in the past. The Index values, obtained using the data collected in the field, were compared with the legal limits (Decree No 115/2003). These legal limits are never given (and it would be useful to report them at least in Table 3).  Methodologically, the work does not bring anything new, but it improves knowledge about the water quality status of the El Salvador River. The data collected and correlation results (which are shown in Figure 2) are simply listed but the reasons (anthropogenic/natural) that condition the chemism at different sampling points are not analyzed in detail.

The Authors merely confirm some correlations (e.g., Water Conductivity/Nitrate), which are, moreover, already known in the bibliography. Limited mention is made of the role exerted by urban discharges (where? Directly into the river? Into groundwater?). In addition, the presence of nitrates in river water is attributed to the action of runoff from soils affected by cultivation. It would be useful, in this regard, to also consider the underground runoff system, which could play a non-negligible role on the chemistry of the whole system.

Chemical analyses were conducted over a rather long period. Although the rainfall figure is fairly consistent (April: 306 mm; May 337.9 mm; June 300.9 mm), the temperature value (which is not shown in Table 3) is variable (row 180 p. 5). Since the temperature figure conditions the water chemism, it would be useful to specify on the basis of what considerations it is not evaluated. Also specify on the basis of what considerations correlations can be made between chemical data for such different periods.

Sampling point 1 is close to a minor watercourse (line 102 p. 5). Has the water quality of this tributary stream been evaluated? Can it influence the water quality characteristics of the water sampled at sampling point 1? It is requested that this aspect be better specified. 

The estimation of the Quality Index should be better detailed. In the text it is told how the QI is calculated (line 174 p. 4) by referring to a graph for which reference is made to the literature (14). It would be more useful to include it in the text for better understanding by the reader.

The discussions are difficult to follow. Reference is made to comparisons with other studies but, for those who are not familiar with the indicated locations, it is really difficult to understand the meaning of such comparisons.

Figure 1 - Unclear. It is recommended that it be redrawn by indicating the toponyms, where possible, on the map

Figure 2 - Caution: the dash on the scale markers is confused with the negative sign

Revise the English by avoiding repetition.

Author Response

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Round 2

Reviewer 1 Report

Dear Authors,

Thank you for addressing most of comments and suggestions addressed by reviewers. I find the readability of the paper has improved by consolidating the material and method section, with the additional information about sample preparation and method validation and the interpretation part was ameliorated.

However, I recommend to:

1.     Change STD by TDS (Total Dissolved Solids).

2.     Equation (1): Add another bracket 𝐖𝐐𝐈 = ∑(𝑺𝑰𝒊 ∗ 𝑾𝒊)

Author Response

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Reviewer 2 Report

The authors have answered the specific comments, but there were no answers/revision provided for the summary (abstract) and conclusions sections.

Before final submission, the authors may consider the general comments (summary&conclusions) to their paper.

As also been mentioned in the previous report, there are no concerns regarding English language. Only a few typos.

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Reviewer 3 Report

The Authors took into account the suggestions made during the first revision.

The work has been supplemented with further analyses and a more appropriate presentation of the results.

Some figures have been improved with appropriate modifications.

The statistical processing of the data has been better treated and commented on.

Further modifications:

In Table 1, the unit of measurement of temperature is not specified.

I reccomend a moderate review of English

Author Response

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