Cost Effectiveness of Ecosystem-Based Nutrient Targets—Findings from a Numerical Model for the Baltic Sea

Round 1

Reviewer 1 Report

Review Report for water

Proposed paper “ Cost effectiveness of ecosystem-based nutrient  targets for a sea – empirical evidence for the Baltic Sea”

Summary

The paper reports on a model-based study designed to identify economic implication of practices in combat eutrophication in the Baltic Sea and adjacent water sheds. The study is based on a numerical model that considers variables representing ecosystem dynamics as well monetary information on economic implications of abatement practices. Three levels of consideration cover sub-basins, countries and the entire Baltic Sea region. Modelling results in numbers on the cost effectiveness of divergent practices at the levels. The numbers are reflected with respect to places and priorities of a future nutrient reduction and ecosystem-based marine management.

Comments in general

Originality/Novelty/Significance:  Nutrient reduction in coastal and shallow marine ecosystems has been a challenging both for researchers and practitioners since the last decades. Despite a growing better understanding of marine ecosystem dynamics, land-sea interactions as well as socio-economic and political implications, reasoning of decision making that includes scientific support for taking effective measures is still an urgent issue. The presented study is embedded into this challenging setting and provides some pieces of novelty.

The topical research question is addressed with a sound methodology. Results are presented with good traceability. These strengths of the study are partly thwarted by weaknesses related to a vague definition of the economic system and, associated to that, somewhat random conclusions (see below for details). 

Interest to the Readers: The study meets the ambitions of the sustainability journal. The topic is relevant for a significant portion of the journal´s readership and an audience beyond.

Merit: Publishing a more mature version of the study can contribute to make further nutrient abatement schemes in the Baltic Sea region more cost effective and more sustainable. Here, the study helps to improve a better understanding of implications of maritime actions and supports future ecosystem-based management of marine and coastal regions.

Scientific Soundness: The paper finds is basis in a sound methodological approach. The authors present a numerical model which is described in an adequate and understandable way. This is particularly a strength of the paper with respect to the ecological part of the model. The variables a chosen carefully and link to relevant functions of both the marine and the terrestrial ecosystems. The considered scenarios for nutrient reduction are relevant and meaningful as well. In contrast to the ecological part, the socio-economic part is somewhat vague and need further elaboration. A revision is recommended to make the latter part sound as well. The paper might benefit on improvements on the following in particular

• The authors introduce the variables that represent processes in the economic realm briefly. The definition of economic variables seems to be driven by the availability of data rather than by an understanding of the socio-economic context of eutrophication and abatement strategies. Of course, a numerical model depends on data, but the design of a model needs to focus at proxies for socio-political and economic key processes or systems dynamics in order to make the model relevant for societal decision making. Such a sketch of the socio-economic system of the Baltic is not provided by the authors. Accordingly, the economic variables are justified in terms of limited processes only. Information on interlinkages or implications for the socio-economic system is missed.
• There is an implication of the fuzzy approach in this paper when taking the socio-economic context into account. The authors highlight certain results of the modelling work. The results are relevant, however, remain fragmented and relate to quite some details or arguments for policy or management recommendations. Here, the monetary numbers make differences in action taking on different levels obvious. Well, the numbers are impressive, but the relation for the different options is more important than the amount of costs. The authors should also clearly indicate that the costs by no way equal the costs likely to occur from real management practices. This is due to the limited number of cost variables in their model compared to the full set of cost items in the Baltic. It would also be worth mentioning more clearly in the paper that the study is focussing at monetary costs. Benefits of abatement schemes that result in non-monetary values are not considered. Decision making is related to such benefits as well.

• The authors leave issues of time unspoken. Well, they have to do so as the numerical model does not cover dimensions in time. Political decisions, on the contrary, often weight time spans specifically. The authors are encouraged to honestly reflect on the significant limitation of their model and results as far as dimensions in time are concerned. This can help practitioners and policy makers to value the findings of this study adequately.

English Level/Quality of Presentation: The paper is structured in an appropriate way. The data and analyses are presented appropriately as well. Some re-working, however, is necessary to realise some linguistic improvements in order to make the text understandable at all points. This relates to several passages in the text where certain words are simply missing. In some sections, grammar is not correctly applied. The help of a native speaker is recommended to make a more precise text easier to read and to avoid unintended connotation.

Links with Special Issues: If an integration in a special issue is intended or needed, the authors are strongly recommended to integrate key terms of the special issues´ topics into the introduction, the reflection on their results and the terms in the discussion section.   

Specific comments

Title: The use of the term ´ecosystem-based´ is somewhat misleading in the present way. Proposal of an alternative title - ´Cost effectiveness of nutrient targets in an ecosystem-based management – findings from a numerical model for the Baltic Sea´

Abstract: line 11- 14 – Sentence hard to understand.

Line 293 Define BOD (Biochemical oxygen demand?)

Author Response

see ci

Author Response File: Author Response.docx

Reviewer 2 Report

The manuscript fits well the scope and the high level of the journal. Just a few remarks:

1. The analysis of recent trends in the balance of nutrients in different sub-basins of the Baltic Sea is incomplete. Referring just to both Bothnian basins does not make much sense. What about the Gdansk or Arkona basins and their recent trends in the balance of nutrients?

2. The description of the role of coastal and transitional waters as nutrient sinks is missing. Refer to Tagliapietra et al. 2020. Emerald Growth: A New Framework Concept for Managing Ecological Quality and Ecosystem Services of Transitional Waters. Water, 12, 894.

Author Response

See enclosed file

Author Response File: Author Response.docx