Dear Ivana Mladenovic and co-authors

I have read your paper:

“Multicriteria Decision Analysis of Sites with Increased Nutrient Contents in Water “

Here are my comments

1- It is no doubt a very important subject, addressing contamination in the most beautiful European River

2- The article provides good and well documented data. I am familiar with your work since I read another similar paper on the Danube, from you, maybe about three years ago.

3- You use the excellent PROMETHEE method and its GAIA extension, which in my opinion, is one of the best, however, it is based on outranking, although GAIA is based on PCA.

According to what you say in page 2, “Given that the problem of water pollution with nutrients is a demanding and multicriteria problem, a multicriteria decision making analysis (MCDA) was used in this work to reveal more information about the mutual dependence between certain parameters of the nutrient indicators and the exact locations where nutrient content is exceeded”.

I assume that your objective is to determine the most polluted sites, something that you don’t say explicitly.

I solved your problem using another MCDM method and obtained this ranking, in descending order of importance:

1-Annual indicator in Novi Sad, that is Total P

2- Minimum indicator in Novi Sad, that is NO2-N

3- Maximum indicator in Smeredovo, that is NH4-N

4- Annual indicator in Radujevac, that is, Annual POH4 -P

5- Minimum indicator in Bezdan, that is, Min NO3-N

6- Minimum indicator in Zemun, that is, Min Total N

7-Limit indicator in Novi Sad, that is, Limit Total N

8- Limit indicator in Bezdam, that is, Limit NO3-N

This ranking shows that the most contaminated site, with P and N, is Novi Sad. Notice that in your Figure 2, with the GAIA graphic, also shows that Novi Sad is the site closest to one of the axes, which, according too GAIA, indicates principal components.

Your ranking is:

1- Novi Sad, that is, Total P

2- Bezdam that is, Min NO3-N

3- Smeretovo, that is, NH4-N

4- Zemun, that is, Min Total N

5-Radujevac, that is, Annual POH4 -P

Consequently, even if both rankings coincide with the best selection, they are different.

I was curious about this difference since you are using very good data and a very well- k own and proved MCDM method.

Naturally, in this case it is impossible to determine which of the two methods employed, (PROMETHEE) on your end, and (SIMUS) on mine, deliver the best solution, and it is not my intention either.

However, there is something that I think can explain the difference. It is the fact that in PROMETHEE all options are considered independently, opposite to SIMUS that takes all of them jointly and interrelated.

This last aspect is for me important, because a river is a highly dynamic and complex system, affected by anthropogenic (domestic and industrial wastes), atmosphere and animal wastes, and thus, probably, among others, contamination, erosion and sediments upstream influence sites downstream.

Thus, the high contamination in Bezdam may be affecting sites as Novi Sad, which in addition, has as a tributary the Drava River that could be contaminated. As I understand, Novi Sad is an important industrial city including and oil refinery, which could explain in part, its pollution.

4-In page 3 you say “information that is provided within the problem, the preferences of a decision-maker, as well as the preferred final outcome of the decision process”

I am afraid that I don’t concur with this statement. This is a real, physical problem and where there is no room for preferences. The experts and DM must, of course, give the appropriate weight to the importance of the different nutrients, and this can be done based on their expertise and examining the consequences of each one, not on preferences, but on expertise, research and analysis.

In my opinion, the DM needs to have a ranking because when doing the sensitivity analysis, to determine the strength of the best option or site, it may be subject to certain criteria than don’t admit and change in their values, which means that the selected option is extremelly vulnerable, and thus, perhaps the second site is more relevant as the most or least contaminate place.

I hope that these comments may help you.

Best regards

Nolberto Munier