The Effects of Reduced Wastewater Load in the Marine Area off Turku in the Archipelago Sea During the Period 1965–2025
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview of Helminen
General comments:
I found this article interesting to read. The English was very clear. The aims and results were clearly stated. It is important that the community should understand that even when we manage to drastically reduce the nutrient input to a body of water, the resulting response is not simple.
There are some area which the author should adjust to make the text easier to follow. I persoannly dislike using weight units for the concentration of nutrients because they are always ambiguous. When you describe a concentration of P in mg/l is is ambiguous. That can be mg of PO4, PO4-P, HPO4, H2PO4 etc. Using mM avoids this problem but I know that the convention of water quality chemists is to use these ambiguous units. Nevertheless it would be appropriate at various places in the text to define exactly what the author mneans by these units i.e. not mg/l but mg PO4-P/l etc etc.
My other somewhat related problem is there should be a section in the methods of how the water concentrations were measured. I realise the data is actually published data of nutrient concentrations measured in other labs. Nonetheless when the author uses the term Total N or Total P it would be helpful to know exactly what was measured and defined by these and similar terms. Was the water filtered before analysis? How was it treated toi get total P etc etc. This need not be a very long description but maybe ~half a page.
Specific comments:
Figure 1 there are no red triangles
Section 2.3 How were nutrient determined
In the text at various places there is mg/l and mg/L. This should be consistently one or the other.
Throughout is total P total dissolved P or does it also contain particulate matter. Likewise for total N. This problem will be solved is there was an expanded method section as requested.
Likewise in lines 406 … how was biomass determined
Determining the limiting nutrient from DIN:DIP ratios. The author is a bid too pessimistic. It is possible to determine the limiting nutrient even during a bloom since the limiting nutrient should be essentially ‘zero’ and the remaining excess nutrient in the water is non-limiting. There can then be complex responses – if the excess is P then cyanobacteria will grow until they consume the excess p.
Comments for author File: 
Comments.pdf
Author Response
Thank you for the constructive feedback. I have endeavored to address all the deficiencies highlighted in the evaluation. In the attached file are my detailed responses to each of the points raised.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsReview for the paper "The effects of reduced wastewater load in the marine area off Turku in the Archipelago Sea, during the period 1965–2025" by Harri Helminen submitted to "Water".
General comments.
This paper analyzes the long-term trend of some important variables reflecting water quality in a coastal water body off Turku, Finland. The study site is located in the Baltic Sea, a semi-enclosed region where land-based currents play a major role in shaping the coastal ecosystem and hydrological regime. Monitoring research, such as that conducted in this study, provides a baseline from which to assess significant changes in the ecosystem in response to environmental fluctuations. Wastewater is one of the main factors determining water quality in coastal areas. Therefore, the control of their loads can be considered as a tool to manage water quality. The paper is based on comprehensive data sets including nutrient concentrations and phytoplankton biomass. The results are interesting and may be of interest to many scientists working in the same regions. However, there is one major flaw that prevents me from recommending that the paper be published as is.
Major flaws.
- Abstract. The main results regarding the trend of phytoplankton biomass and nutrients should be included in this part.
- Introduction. I suggest a part emphasizing the novelty and importance of the research in a global context, e.g. some examples of similar regions with the same problems should be outlined as reference sites.
- Materials and methods. I did not understand the origin of the nutrient data. I have visited the link provided (https://www.syke.fi/avoindata) and was not able to obtain the data mentioned. In addition, the site is in Finnish and difficult to read for many international readers. Therefore, I suggest including a description of the methods, procedures and sample sizes for nutrient data. The main environmental characteristics of selected monitoring stations (180, 200, 210, etc.) need to be presented in a separate table.
- Materials and methods. The phytoplankton data set and analysis are not well described. Provide a sampling period and total sample size. Indicate which instrument was used to sample phytoplankton, depths of sampling, frequency of sampling. Also, I saw that the stations were located in different regions that seemed to be different if hydrological variables. Therefore, provide validations that there were no differences in phytoplankton between different sampling sites. All equipment used to observe and analyze phytoplankton should be indicated. A brief overview of the methods used to identify and count phytoplankton must be included in the MS. Describe the methods used to convert abundance to biomass data. Specify the units for phytoplankton biomass (wet, dry, or carbon). The author mentioned that only summer phytoplankton samples were analyzed, while other variables are presented as winter, summer, spring, and fall estimates. How did summer phytoplankton biomass reflect seasonal changes in water quality?
- Materials and Methods. My main concern is the lack of statistical treatment of the data. The author provides many plots showing time series of nutrient, environmental and phytoplankton variables. However, there is no relevant statistical analysis of these trends. I suggest using appropriate methods to explore the main patterns. For example, Mann-Kendall test should be performed on all trend data sets. ARIMA or wavelet analysis can also be used to visualize long-term changes. Comparisons between time periods should be made using relevant criteria such as ANOVA or Kruskal-Wallis tests. Regression analysis should be applied to other variables in addition to Chl-a-P relationships. In addition, an ordination of environmental and phytoplankton data may be used to delineate different time periods. The main results presented without any statistical validation look like unsupported speculations and I encourage the author to perform relevant analyses.
- Discussion. The discussion should outline the ecological implications of the main findings.
- Discussion. Discuss the applicability of your results to other similar ecosystems and regions.
Specific remarks.
Introduction. L87. Blue-green algae. More relevant term is cyanobacteria. Consider replacing.
M&M. Section 2.2. L103-109 and L110-114. Provide relevant references.
Figure 1. Coordinate girds shall be added to the map.
L407. Incorrect reference. Should be Figure 23 instead of Figure 22.
Figures 2-5, 7-21, 24. Left axes are not visible. Please correct.
Figure 25. Add sample size (n) to the graph.
Author Response
Thank you for the constructive feedback. I have endeavored to address all the deficiencies highlighted in the evaluation. In the attached file are my detailed responses to each of the points raised.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe authors have modified the text as I suggested and it should now be published
Reviewer 2 Report
Comments and Suggestions for AuthorsNo further comments.
