Developing Indicators for the Valuation of River Ecosystem Services

Abstract

River ecosystems provide essential services that sustain human well-being and ecological integrity, yet their contributions are often underestimated in management and policy decisions. This study aims to develop and validate indicators for quantifying river ecosystem services to support evidence-based decision-making. A review of previous studies was conducted to compile a preliminary list of indicators. Expert evaluations were then applied using the Analytical Hierarchy Process (AHP) and content validity ratio (CVR) analysis to assess their representativeness and reliability. The results identified priority indicators across provisioning, regulating, and cultural services. The findings revealed that, in the AHP analysis, regulating services received the highest weight (0.4567), followed by provisioning services (0.3811) and cultural services (0.1622). In the CVR analysis, four valid indicators were identified for provisioning services, sixteen for regulating services, and eight for cultural services. These findings highlight the importance of careful indicator selection and methodological transparency. The study contributes a refined set of indicators that can inform river restoration initiatives, sustainable water management, and integration into national ecosystem accounting systems.

1. Introduction

Aquatic ecosystems provide a variety of ecosystem services that play a critical role in maintaining a healthy society and environment [1]. In particular, river ecosystems, as transitional zones where terrestrial and aquatic systems meet, constitute a fundamental ecological system by mediating watershed connectivity and material circulation [2]. However, over the past few decades, aquatic ecosystems worldwide have undergone rapid changes. Human activities caused by industrialization and urbanization, coupled with changes in precipitation patterns and rising water temperatures due to climate change, have posed serious threats to the health of aquatic ecosystems [3,4]. Such changes are not confined to the ecological dimension but also extend to human society, leading to threats to safety, welfare, and even significant economic losses [5,6,7]. Accordingly, there is a pressing need to quantitatively assess the services provided by aquatic ecosystems and to translate the impacts of human activities into economic values in order to measure the losses or gains resulting from ecosystem changes [8].

To define the direct and indirect benefits that river ecosystems and biodiversity provide to humans, the concept of ecosystem services is employed. The Millennium Ecosystem Assessment [9] established the classification of ecosystem services into provisioning, regulating, supporting, and cultural services. However, supporting services have been criticized for being indirectly related to human well-being and for potentially being double-counted with other services [10]. Consequently, recent international frameworks have tended to classify ecosystem services into three major categories: provisioning services such as the supply of food (e.g., fish, shellfish, and crustaceans), freshwater, and hydropower; regulating services such as water purification and flood mitigation; and cultural services such as ecotourism, recreation, and landscape enjoyment [11,12].

Although many studies have attempted to evaluate the value of river ecosystem services based on these classifications, most have focused on individual service items [13,14], and thus, comprehensive and ecosystem-specific indicator systems remain limited. Internationally, several classification systems such as the Common International Classification of Ecosystem Services (CICES) and the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) framework have been proposed. Nonetheless, specific and applicable evaluation indicators tailored to river ecosystems are still lacking. Moreover, many of the indicators employed in previous studies rely on non-market valuation methods, particularly choice experiments and contingent valuation surveys [15], which, while useful, pose challenges in terms of establishing official and standardized criteria, thereby limiting their applicability [14,16]. A representative methodological approach to overcome these challenges is integrated assessment. Integrated assessment is a systematic framework that traces and evaluates the pathway from human activities to environmental quality changes, receptor responses, and economic value changes. It enables a comprehensive understanding of the socio-economic implications of changes in ecosystem services. Given that rivers constitute interconnected and complex socio-ecological systems, integrated assessment plays a critical role in measuring river ecosystem services.

Against this backdrop, the present study aims to develop credible evaluation indicators for riverine ecosystem services by conducting Analytic Hierarchy Process (AHP) and Content Validity Ratio (CVR) analyses with expert groups, in linkage with reliable statistical data. The proposed indicator system can serve as a foundation for the quantitative assessment and valuation of aquatic ecosystem services [17]. Furthermore, by aligning these indicators with internationally standardized classification frameworks, this study is expected to contribute to the establishment of sustainable water management strategies across diverse countries and regions. Ultimately, the findings will provide essential academic and policy-oriented evidence for the conservation and restoration of aquatic ecosystems and for responding to climate change worldwide.

2. Materials and Methods

2.1. Indicator Selection

In this study, a pool of candidate indicators was derived based on reports and studies on the evaluation of aquatic ecosystem services conducted by major domestic and international institutions, including the Integrated System for Natural Capital and Ecosystem Services Accounting (INCA) of the European Union, Water Europe, the International Hydrology Series (Cambridge), the European Commission, the Freshwater Information System, and the Korea Environment Institute (KEI). These reports systematically classified the types of aquatic ecosystem services—covering provisioning, regulating, and cultural services—and suggested measurable indicators for quantitative assessment. Accordingly, these were utilized in establishing the candidate pool of indicators for this study.

However, existing research presents several limitations. First, some studies proposed indicators without considering the availability of actual statistical data, thereby reducing their applicability. Second, several indicators failed to directly correspond to the quantification of specific types of aquatic ecosystem services. Moreover, the scope and definitions of indicators varied across institutions, making cross-comparison within the same service category difficult, while their applicability to different regions has not been sufficiently validated. To address these limitations, the present study restructured the candidate pool of indicators by reviewing those suggested in prior research and applying the criterion of data availability. In particular, data availability was determined based on whether officially published statistics were provided at the level of administrative districts or river basins.

2.2. Survey Outline

To derive indicators for evaluating riverine ecosystem services, an expert survey was conducted between 7 and 25 July 2025 via an online survey system. A total of 300 experts participated. Respondents were limited to specialists in fields directly related to aquatic ecosystems, including ecology and biology, environmental and river management, landscape architecture and scenery, as well as other related disciplines. Experts from academia, government agencies, and public and private research institutions were included to ensure a diverse expert base. To recruit participants, cooperation was sought through academic societies and professional associations related to aquatic ecosystems, such as those in ecology, environmental engineering, river management, and landscape architecture. Invitations were distributed to relevant experts identified through these networks, resulting in 300 valid responses collected for the analysis.

The questionnaire comprised two parts. PART A aimed to evaluate the relative importance of ecosystem service categories and their sub-indicators using pairwise comparisons based on Saaty (1990) [18] widely adopted nine-point scale, as shown in

Table 1. Example of Pairwise Comparison Method in Part A.

Item A	Extremely Preferred	Very Strongly Preferred	Strongly Preferred	Moderately Preferred	Indifferent	Moderately Preferred	Strongly preferred	Very Strongly Preferred	Extremely Preferred	Item B
	9	7	5	3	1	3	5	7	9

. To minimize inconsistencies during the response process, the system was designed to automatically verify transitive consistency among pairwise comparisons. For instance, if a respondent indicated that provisioning services were more important than regulating services, and regulating services were more important than cultural services, the system automatically presented the logical inference that provisioning services were more important than cultural services, thereby ensuring a consistent response structure. Furthermore, the survey was designed to allow respondents to revise previous answers by returning to earlier steps when necessary, thereby enabling self-correction and enhancing response reliability.

PART B was designed to evaluate the validity of candidate indicators for each sub-item. The criteria for assessing representativeness were: (1) whether there was a direct correlation or association between the indicator and the specific ecosystem service attribute; and (2) whether official statistical data were available for the indicator. Based on these criteria, the survey assessed whether the candidate indicators adequately captured the targeted ecosystem service items. Representativeness was evaluated on a five-point Likert scale (1 = not at all appropriate, 5 = very appropriate), as shown in

Table 2. Example of Evaluation Criteria for Representativeness in Part B.

Candidate Indicator	Strongly Agree	Agree	Neutral	Disagree	Strongly Disagree
	5	4	3	2	1

. The quantitative validity of each indicator was then examined using experts’ responses. In the subsequent analysis stage, the Content Validity Ratio (CVR) method was applied to determine the final validity of each indicator.

In cases where only one candidate indicator was identified for a given item, comparisons of representativeness could not be made. To address this, open-ended questions were included to allow experts to suggest additional indicators they deemed appropriate beyond those initially proposed by the researchers.

2.3. Analytical Framework: AHP–CVR Analysis

The Analytic Hierarchy Process (AHP) is a multiple-criteria decision-making (MCDM) method developed to evaluate complex alternatives by structuring evaluation criteria hierarchically and assigning relative weights according to the hierarchy [19]. It is widely applied to determine priorities among multiple items and is regarded as one of the most theoretically robust decision-making techniques currently available [20]. The AHP procedure can be divided into four steps [19]. First, the hierarchical structure of the overall objective must be established [21,22]. In this study, aquatic ecosystem services were defined as the top-level goal. The second level comprised the three service categories—provisioning, regulating, and cultural services—while the third level included sub-indicators corresponding to each service category. Second, expert surveys were conducted to apply AHP. Experts were asked to conduct pairwise comparisons of the relative importance of two items at a time, thereby allowing the derivation of numerical priorities. Saaty (1990) [18] nine-point scale, the most widely used metric for such comparisons, was applied. Third, weights for each item were calculated. This study employed the geometric mean method (also known as the Logarithmic Least Squares Method, LLSM) proposed by Crawford and Williams (1985) [23]. The importance score $v_i$ for item i was calculated as the geometric mean of all comparison values in the corresponding row by taking the $n$ -th root of their product. Subsequently, the derived geometric mean was divided by the sum of all geometric means to obtain the normalized weight $w_i$. The calculation formulas are as follows:

$$v_i= {\left({\prod }_{j=1}^n{a}_{ij}\right)}^{{\displaystyle \frac{1}{n}}}$$

(1)

$$w_i={\displaystyle \frac{v_i}{{\sum }_{k=1}^n{v}_k}}$$

(2)

This computation was implemented using Python 3.13. Fourth, the consistency of the judgment matrix was verified by calculating the Consistency Ratio (CR) [22]. The CI and CR were calculated as follows:

$$\mathrm{CI} = {\displaystyle \frac{{\lambda }_{max }-n}{n-1}}$$

(3)

$$\mathrm{CR}={\displaystyle \frac{CI}{RI}}$$

(4)

Here, CI denotes the Consistency Index, which is calculated as the difference between the maximum eigenvalue of the judgment matrix and the number of comparison items n. When the matrix is perfectly consistent, λmax = n. Thus, the greater the difference, the higher the degree of inconsistency. CR is obtained by dividing the calculated CI by the Random Index (RI) of a randomly generated judgment matrix, using Saaty’s RI values. A CR value of 0.1 or less was considered acceptable for ensuring the reliability of the results [24]. Through this verification, the automated transitive consistency logic implemented in the online survey was re-examined to ensure the reliability of responses.

Subsequently, the validity of indicators for quantifying sub-items was examined using the CVR method, based on the results of Part B of the survey. The CVR value was calculated as follows:

$$\mathrm{CVR} = {\displaystyle \frac{n_e-\frac{N}{2}}{\frac{N}{2}}}$$

(5)

The CVR value was calculated using the following formula, reflecting $n_e$, the number of panelists who selected “agree” or “strongly agree,” out of the total number of panelists N. The CVR value ranges from −1 to +1: a positive value indicates that more than half of the experts judged the indicator to be valid, a negative value indicates the opposite, and zero indicates that exactly half of the experts deemed the indicator valid [25]. The minimum threshold CVR varies depending on the number of experts [26]. Lawshe (1975) [25] suggested a threshold of 0.29 when the panel size is 40, with at least 50% consensus required on sociological grounds. In this study, since 300 experts participated, any indicator with a CVR greater than zero was considered valid.

3. Results

3.1. Result of Indicator Selection

Based on a review of major domestic and international reports—including those by INCA, Water Europe, the International Hydrology Series, the European Commission, and the Korea Environment Institute—candidate indicators for evaluating aquatic ecosystem services were derived (

Table 3. Results of Candidate Indicator Derivation.

Ecosystem Service Category	Service Item	Sub-Item	Candidate Indicator	Data Availability	Source
Provisioning services	Food	Fishery products	Fish production	Y	European Commission International Hydrology series Korea Environment Institute
		Edible plants/animals, dietary fibers (excluding fishery products)	Crop production	Y
	Energy production	Hydropower	Hydropower generation	Y	INCA European Commission
			Hydropower facilities	Y
		Biomass utilization	Biomass harvesting	N
	Freshwater supply	Direct or indirect use of freshwater	Storage and retention of water	Y	Water Europe European Commission International Hydrology series INCA Korea Environment Institute
			Water for drinking purposes	N
			Water use volume (domestic, industrial, agricultural)	Y
	Raw materials	Fiber, aggregates, timber	River aggregate extraction	Y	Korea Environment Institute
			Wood production	Y	International Hydrology series (Cambridge)
	Mineral resources	Metals, non-metals, coal	Mineral production	Y	Korea Environment Institute
Regulating services	Climate regulation	Microclimate regulation	Daily/monthly evapotranspiration	Y	Korea Environment Institute
			Water temperature	Y	Korea Environment Institute
		Carbon regulation	Carbon sequestration	N	Water Europe
	Water purification	Purification by river flow/velocity	10-year average storage	Y	Water Europe European Commission Korea Environment Institute
			Riverbed slope	Y
			Catchment elevation ratio	Y
			Mean velocity	Y
			Streamflow	Y
			Achievement of “good water” standards	Y
			Total phosphorus reduction	Y
			Total nitrogen reduction	Y
	Water quantity regulation	Regulation via water supply/circulation	Soil moisture value	N	Korea Environment Institute International Hydrology series (Cambridge) European Commission INCA
			Achievement rate of environmental flow	Y
			Groundwater use	Y
			Mean annual flow/Baseflow	Y
			River volume	N
	Disaster regulation	Flood, drought, wildfire prevention/mitigation	natural water retention	Y	Water Europe European Commission Korea Environment Institute
			Damage costs from droughts and floods	Y
			Levee height/installation rate	Y
			Expected inundation area during floods	Y
Cultural services	Ecotourism	River ecotourism	Number of ecotourism sites	Y	INCA European Commission Korea Environment Institute
			Number of visitors	Y
	Recreation/leisure	Hydrophilic activities and river space utilization	Levels of hydrophilic activities (e.g., water sports, fishing, cycling, walking/jogging)	Y	European Commission Korea Environment Institute
			Status of riverfront spaces (parks, playgrounds, sports fields)	Y
			Annual cultural festivals	Y
			Proximity to rivers/lakes	N
			Tourism revenue	N
	Education/science	Educational/scientific use of river ecosystems	Number of educational facilities and program users	Y	INCA Korea Environment Institute
	Landscape aesthetics	Visual landscape	Number of rivers designated among the “100 Beautiful Rivers of Korea”	Y	INCA Korea Environment Institute
			Status of ecological landscape conservation areas	Y
			Number of observation decks along rivers	N
			Number of properties with views of natural landscapes	N
	Religious/cultural heritage	Historical, religious, cultural identity	Number of designated cultural heritage sites by watershed	Y	Water Europe Korea Environment Institute
			Number of artworks	Y

). Aquatic ecosystem services were categorized into three groups (provisioning, regulating, cultural), excluding supporting services, which represent intermediate ecological processes rather than direct benefits to humans, and for each category, sub-items and corresponding candidate indicators were identified. For each indicator, the availability and source of statistical data were examined to retain only those indicators that are practically applicable.

For provisioning services, indicators were identified for food, energy production, freshwater supply, raw materials, and mineral resources. The food sub-item was divided into fishery products and other edible plants/animals, dietary fibers, represented respectively by Fish production and Crop production, both with available statistics. Energy production comprised hydropower and biomass utilization: for hydropower, Hydropower generation and Hydropower facilities were retained with available data, whereas Biomass harvesting lacked statistical data. For freshwater supply, Storage and retention of water, Water for drinking purposes, and Water use volume (domestic/industrial/agricultural) were considered; among these, data for drinking water supply were not available. For raw materials (fibers, aggregates, timber), River aggregate extraction and Wood production were retained with available data. For mineral resources, Mineral production (metals, non-metals, coal) was supported by available statistics.

For regulating services, indicators were derived for climate regulation, water purification, water quantity regulation, and disaster regulation. Climate regulation included microclimate and carbon regulation, represented by Daily/monthly evapotranspiration, Water temperature, and Carbon sequestration. While data were available for evapotranspiration and water temperature, data for carbon sequestration were not. For water purification by river flow/velocity, indicators with available statistics included 10-year average storage, Riverbed slope, Catchment elevation ratio, Mean velocity, Streamflow, Achievement of “good water” standards, Total phosphorus reduction, and Total nitrogen reduction. The “good water” indicator reflects compliance with environmental standards for BOD, TOC, and T-P and was applied as an indicator of surface water quality. Water quantity regulation—defined as regulation via water supply and circulation—was represented by Soil moisture value, Achievement rate of environmental flow, Groundwater use, Mean annual flow/Baseflow, and River volume. Among these, data were available for environmental flow, groundwater use, and Mean annual flow/Baseflow, but not for soil moisture and river volume. Disaster regulation included Natural water retention, Damage costs from droughts and floods, Levee height/installation rate, and Expected inundation area during floods; all were supported by available statistics.

For cultural services, indicators were identified for ecotourism, recreation/leisure, education/science, landscape aesthetics, and religious/cultural heritage. For ecotourism, Number of ecotourism sites and Number of visitors were retained; the former is supported by statistics and the latter by visitor-demand estimates. Recreation/leisure focused on hydrophilic activities and river space utilization and included Levels of hydrophilic activities (e.g., water sports, fishing, cycling, walking/jogging), Status of riverfront spaces (parks, playgrounds, sports fields), Annual cultural festivals, Proximity to rivers/lakes, and Tourism revenue. Data were available for activity levels, riverfront spaces, and festivals, but not for proximity or tourism revenue. For education/science, Number of educational facilities and program users was supported by available statistics. For landscape aesthetics, indicators included Number of rivers designated among the “100 Beautiful Rivers of Korea”, Status of ecological landscape conservation areas, Number of observation decks along rivers, and Number of properties with views of natural landscapes; the last two lacked data. Finally, for religious/cultural heritage, Number of designated cultural heritage sites by watershed and Number of artworks were supported by available statistics. In this study, indicators without available statistical data were excluded from further analysis, as the research aimed to establish a set of practically applicable indicators that can be evaluated using officially collected and verifiable statistical information. Therefore, only indicators with accessible data sources were used to construct the indicator framework and applied in the expert survey for value assessment.

3.2. Result of AHP Analysis

An AHP analysis was conducted using pairwise comparisons among items derived from prior research to assess the relative importance of aquatic ecosystem services (

Table 4. Results of the AHP Analysis.

Item	Sub-Item	Importance Weight
aquatic ecosystem services (CR = 0.0005)	regulating services	0.4567
	provisioning services	0.3811
	cultural services	0.1622
provisioning services (CR = 0.0055)	Freshwater supply	0.3737
	Food	0.2025
	Energy production	0.1559
	Raw materials	0.0943
	Medicinal and genetic resources	0.0919
	Mineral resources	0.0816
regulating services (CR = 0.0014)	Water supply/quantity regulation	0.3277
	Disaster regulation	0.2552
	Water purification	0.1994
	Climate regulation	0.1152
	Biological regulation	0.1025
cultural services (CR = 0.0006)	Educational/scientific value	0.2524
	Landscape aesthetics	0.2286
	Ecotourism	0.2073
	Recreation/leisure	0.1903
	Religious/cultural heritage	0.1213

). At the top level, regulating services received the highest weight (0.4567), followed by provisioning services (0.3811) and cultural services (0.1622), with a consistency ratio (CR) of 0.0005. These results indicate that experts prioritized functions directly tied to public safety—such as disaster prevention, water purification, and water quantity regulation—over tangible resource provision (e.g., food and raw materials).

At the sub-item level within provisioning services, freshwater supply (0.3737) was rated highest, followed by food (0.2025), energy production (0.1559), raw materials (0.0943), medicinal and genetic resources (0.0919), and mineral resources (0.0816) (CR = 0.0055). Within regulating services, water supply/quantity regulation (0.3277) ranked highest, followed by disaster regulation (0.2552), water purification (0.1994), climate regulation (0.1152), and biological regulation (0.1025) (CR = 0.0014). These weights are consistent with growing concerns about extreme hydro-climatic hazards—such as floods and droughts—under climate change. Within cultural services, educational/scientific value (0.2524) ranked highest, followed by landscape aesthetics (0.2286), ecotourism (0.2073), recreation/leisure (0.1903), and religious/cultural heritage (0.1213) (CR = 0.0006). This result can be interpreted as a reflection of growing social interest in the environment, whereby rivers are increasingly recognized not merely as resources for leisure and tourism but rather for their educational and scientific value. In addition, since this study was conducted based on an expert survey, the findings are likely to reflect the perspectives of experts who place particular emphasis on educational value.

3.3. Result of CVR Analysis

In this study, a Content Validity Ratio (CVR) analysis was conducted for the candidate indicators of aquatic ecosystem services derived earlier, based on the results of the expert survey. The CVR analysis is a procedure to verify whether each indicator can validly represent the corresponding service item, and it was calculated using the proportion of experts who responded “agree” or “strongly agree.” A positive CVR indicates that the representativeness of the indicator is high, whereas a negative CVR suggests that the validity of the indicator is relatively low.

The analysis results (

Table 5. Results of the Content Validity Analysis.

Ecosystem Service Category	Service Item	Sub-Item	Candidate Indicator	Number of Respondents Who Answered ‘Agree’ or ‘Strongly Agree’ on Indicator Representativeness	CVR
Provisioning services	Energy production	Hydropower	Hydropower generation	217	0.447
			Hydropower facilities	173	0.153
	Freshwater supply	Direct or indirect use of freshwater	Storage and retention of water	262	0.747
			Water use volume (domestic, industrial, agricultural)	273	0.82
	Raw materials	Fiber, aggregates, timber	River aggregate extraction	132	−0.12
			Wood production	73	−0.513
Regulating services	Climate regulation	Microclimate regulation	Daily/monthly evapotranspiration	205	0.367
			Water temperature	221	0.473
	Water purification	Purification by river flow/velocity	10-year average storage	177	0.18
			Riverbed slope	190	0.267
			Catchment elevation ratio	136	−0.093
			Mean velocity	252	0.68
			Streamflow	253	0.687
			Achievement of “good water” standards	252	0.68
			Total phosphorus reduction	247	0.647
			Total nitrogen reduction	241	0.607
	Water quantity regulation	Regulation via water supply/circulation	Mean annual flow/Baseflow	248	0.653
			Achievement rate of environmental flow	248	0.653
			Groundwater use	187	0.247
	Disaster regulation	Flood, drought, wildfire prevention/mitigation	natural water retention	234	0.56
			Damage costs from droughts and floods	240	0.6
			Levee height/installation rate	226	0.507
			Expected inundation area during floods	249	0.66
Cultural services	Ecotourism	River ecotourism	Number of ecotourism sites	170	0.133
			Number of visitors	177	0.18
	Recreation/leisure	Hydrophilic activities and river space utilization	Levels of hydrophilic activities (e.g., water sports, fishing, cycling, walking/jogging)	229	0.527
			Status of riverfront spaces (parks, playgrounds, sports fields)	238	0.587
			Annual cultural festivals	165	0.1
	Landscape aesthetics	Visual landscape	Number of rivers designated among the “100 Beautiful Rivers of Korea”	175	0.167
			Status of ecological landscape conservation areas	220	0.467
	Religious/cultural heritage	Historical, religious, cultural identity	Number of designated cultural heritage sites by watershed	190	0.267
			Number of artworks	102	−0.32

) are as follows. For provisioning services, indicators related to hydropower included Hydropower generation and Hydropower facilities (installed capacity), while indicators related to the direct or indirect use of freshwater included Water use volume and Storage and retention of water. Among these, Water use volume recorded the highest CVR value of 0.82, followed by Storage and retention of water. Next, Hydropower generation (0.447) and Hydropower facilities (0.153) were also shown to have content validity. In contrast, for raw materials such as fibers, aggregates, and timber produced in rivers, both River aggregate extraction and Wood production yielded negative CVR values, indicating low validity as representative indicators. This suggests that experts judged these indicators to be insufficient in representing the provisioning services of rivers that provide raw materials such as fibers, aggregates, and timber.

For regulating services, indicators related to water supply and circulation included Mean annual flow and Achievement rate of environmental flow, both of which showed CVR = 0.653 and were deemed valid, followed by Groundwater use (0.247). For microclimate regulation, Water temperature (0.473) and Daily/monthly evapotranspiration (0.367) were derived as valid indicators to quantify microclimate regulation. It is assumed that Water temperature yielded higher content validity because it is relatively easier to observe directly. For disaster regulation, indicators included Expected inundation area during floods (0.66), Damage costs from droughts and floods (0.6), Effective storage capacity of flood-control facilities (0.56), and Levee height/installation rate (0.507), all of which were found valid for quantitatively representing disaster regulation services. For water purification, Streamflow (0.687), Mean velocity (0.68), Achievement of “good water” standards (0.68), Total phosphorus reduction (0.647), and Total nitrogen reduction (0.607) all recorded content validity above 0.6. In addition, Riverbed slope (0.267) and 10-year average storage (0.18) showed relatively lower values but were still applicable as indicators representing water purification. On the other hand, the Catchment elevation ratio produced a negative value, suggesting limitations in explaining and interpreting services directly. In other words, indicators related to topographic features, such as riverbed slope and catchment elevation ratio, showed low representativeness.

For cultural services, indicators related to hydrophilic activities and the utilization of river spaces included Status of riverfront spaces (parks, playgrounds, sports fields), which recorded the highest CVR value of 0.587, followed by Levels of hydrophilic activities (e.g., water sports, fishing, cycling, walking/jogging) at 0.527. In addition, Annual cultural festivals recorded a relatively low value of 0.1, but was still considered valid as an indicator. For landscape aesthetics, Status of ecological landscape conservation areas (0.467) and Number of rivers designated among the “100 Beautiful Rivers of Korea” (0.167) were shown to be applicable as indicators. For ecotourism-related indicators, Number of visitors (0.18) and Number of ecotourism sites (0.133) were derived, but both showed relatively low content validity. Finally, for religious and cultural heritage, Number of designated cultural heritage sites by watershed recorded 0.267, while Number of artworks recorded −0.32, indicating low validity. The low score for Number of artworks can be interpreted as due to the ambiguity in defining the category of artworks, making it difficult to use this indicator to represent the historical, religious, and cultural identity of rivers and watersheds.

4. Discussion

With the intensification of the climate crisis, water-related problems such as water shortages and disturbances in aquatic ecosystems have become increasingly urgent. Consequently, the quantification of riverine ecosystem services has gained importance for developing policies and management strategies. The United Nations developed the System of Environmental-Economic Accounting (SEEA) framework to systematically compile data on habitats and landscapes, and to measure ecosystem service flows and ecosystem asset changes in both physical and monetary terms, linking them to the economy and human activities. The SEEA Ecosystem Accounting (SEEA EA) quantifies ecosystem contributions through ecosystem accounts on extent, condition, service flows (physical and monetary accounts), and assets. These accounts have been applied in diverse decision-making contexts, including policy evaluation, cost–benefit analysis, and monitoring of the Sustainable Development Goals (SDGs). In practice, examples include Indonesia’s peatland carbon accounts, South Africa’s river ecosystem accounts, and Uganda’s species accounts, all of which have utilized SEEA to support national-level policies [27]. Against this backdrop of expanding international efforts, the present study sought to develop river ecosystem service indicators linked to available statistical data, thereby offering a method for quantitative evaluation.

The analysis results first showed that regulating services were considered more important than provisioning or cultural services. This indicates that experts recognized the functions of rivers that are directly connected to public safety as being more critical than their resource-provisioning functions. This finding can be interpreted in relation to the increasing frequency of climate-related natural disasters worldwide, such as extreme floods, droughts, and river overflows. These disasters remind us that the loss of regulating functions in rivers can lead to immense socio-economic damages, and experts appear to have reflected this perception in rating regulating services as the most important. Within regulating services, the high weights of Water supply/quantity regulation (0.3277) and Disaster regulation (0.2552) further highlight that stable water management and disaster response are core tasks for river management in the era of the climate crisis. This result can also be explained by the increasing urgency of water-related risks under the climate crisis. Water supply and quantity regulation reflect the importance of maintaining stable hydrological conditions to ensure continuous water availability for domestic, agricultural, and industrial uses, especially under changing rainfall patterns. Meanwhile, Disaster regulation captures the river’s capacity to mitigate flood and drought damages by buffering extreme hydrological fluctuations and maintaining ecosystem resilience. The high weights assigned to these two indicators suggest that experts perceive water security and disaster prevention as the most immediate and tangible benefits provided by river ecosystems in the current climate context.

The next most important category, provisioning services, was largely explained by the intuitive importance of directly usable resources such as Freshwater supply (0.3737) and Food (0.1559), which are essential for human livelihoods and industrial activities. In the CVR analysis, these resources also demonstrated high validity, as indicators such as Water use volume and Storage and retention of water are supported by official statistics and show a clear, intuitive relationship with the services they represent. In contrast, indicators such as Wood production, which is influenced by external factors including climate conditions, land use, and forest management, and River aggregate extraction, which raises concerns over environmental degradation, sustainability, and lack of ecosystem specificity, were judged to be unsuitable as representative indicators of river ecosystem provisioning services.

Finally, for cultural services, Educational/scientific value (0.2524) was rated as the most important. This outcome may reflect the composition of the expert survey, in which more than half of the respondents were academics who may place higher value on educational aspects. It is notable that cultural services have often been evaluated indirectly in previous studies—through willingness-to-pay surveys or other non-market valuation methods—or have been relatively under-quantified compared to other ecosystem services [14]. However, this study demonstrated that cultural services can be quantitatively assessed using official statistical data, including Number of ecotourism sites, Number of visitors, Status of ecological landscape conservation areas, and Number of designated cultural heritage sites by watershed. This finding meaningfully complements the conventional perception that cultural services are inherently difficult to quantify.

Furthermore, this approach demonstrates that the evaluation of aquatic ecosystem services need not remain confined to academic discussion but can provide a practical foundation for policy and management decision-making. In particular, as the risks associated with the climate crisis and water resources intensify, the process of independently estimating the economic value of each service and linking it to broader socio-economic impacts can serve as a practical decision-making tool in diverse areas, such as water management policy, feasibility studies for restoration projects, and the prioritization of financial investments. Through ecosystem service valuation, decision makers can better clarify the benefits that nature provides to people and make rational and balanced choices by considering economic, social, and environmental objectives [28]. For example, Terrado et al. (2016) demonstrated in the Llobregat River Basin, Spain, that ecosystem service-based evaluation can effectively guide the prioritization of management actions such as environmental flows and wastewater treatment [29].

Comparing the results of this study with other previous studies, Pastor et al. (2022) [30] developed a spatial assessment framework for major Chinese river basins using indicators derived from previous research to analyze socio-ecological drivers of river ecosystem services. Grizzetti et al. (2019) [31] quantified six key services—Water provisioning (for drinking and non-drinking), Water purification, Erosion prevention, Flood protection, Coastal protection, and Recreation and tourism—across European freshwater and coastal ecosystems. However, their study relied primarily on model- and estimation-based indicators rather than official statistical data, which limits direct comparability and policy application at the international level. In contrast, the present study integrated expert weighting (AHP) and statistical validity testing (CVR) to establish a standardized indicator hierarchy directly linked to national official statistics, thereby enhancing reproducibility, transparency, and policy applicability. This approach also directly responds to Hanna et al. (2018) [14], who emphasized that validated and reproducible data, methods, and indicators with transparent documentation are essential for credible ecosystem service quantification. Consistent with previous global findings, the high relative importance of regulating services in this study supports the view that regulatory functions are fundamental to maintaining ecosystem stability and societal safety. Moreover, by constructing a standardized, statistically verified indicator system grounded in official data, this study moves beyond spatial or model-based analyses to provide a policy-relevant framework for integrating aquatic ecosystem service evaluation into river management and decision-making.

Nevertheless, one point of caution in ecosystem service quantification is that indicators should not be simply aggregated [32]. If aggregated indiscriminately, the overall value is likely to be overestimated as the number of service items increases. Therefore, the application of river ecosystem service indicators should be embedded within an Integrated Assessment framework. Integrated assessment traces the pathway of “human activity—changes in environmental quality—impacts on receptors,” enabling the quantification of ecosystem service changes caused by human activities (e.g., land cover/use changes, pollutant emissions) and their conversion into economic values to inform policy and project decisions. Such an integrated approach provides higher scientific validity than simple indicator aggregation, as it can reflect interactions and trade-offs among services. At the same time, it allows consideration of the ripple effects of aquatic ecosystem service changes on socio-economic systems, thereby serving as a substantive basis for cost–benefit analysis of water management policies and feasibility assessments of river-related projects. Through integrated assessment, the evaluation of river ecosystem services can move beyond academic discourse to make practical contributions to policy design and the establishment of sustainable water management strategies in the era of the climate crisis.

5. Conclusions

River ecosystems provide essential services—such as water supply, flood mitigation, and water purification—that directly contribute to ecological stability and human well-being. However, increasing anthropogenic pressures and climate-induced hydrological changes have intensified the need for policies and projects to maintain and restore river ecosystem services. Because these services are not traded in markets, their value must be quantitatively assessed to guide management priorities and policy decisions, and such evaluations are increasingly being incorporated into global environmental governance [33,34,35]. This study quantitatively evaluated river ecosystem services by integrating Analytic Hierarchy Process (AHP) and Content Validity Ratio (CVR) analyses with official statistical data. The findings revealed that, in the AHP analysis, regulating services were rated as more important than provisioning and cultural services. Within each category, Water supply/quantity regulation (0.3277) ranked highest in regulating services, Freshwater supply (0.3737) in provisioning services, and Educational/scientific value (0.2524) in cultural services. In the CVR analysis, indicators identified as valid for provisioning services included Hydropower generation, Hydropower facilities, Water use volume (domestic, industrial, agricultural), and Storage and retention of water. For regulating services, valid statistical indicators included Daily/monthly evapotranspiration, Water temperature, 10-year average storage, Riverbed slope, Mean velocity, Streamflow, Achievement of “good water” standards, Total phosphorus reduction, Total nitrogen reduction, Achievement rate of environmental flow, Groundwater use, Natural water retention, Damage costs from droughts and floods, Levee height/installation rate, and Expected inundation area during floods. For cultural services, valid indicators included Number of ecotourism sites, Number of visitors, Levels of hydrophilic activities (e.g., water sports, fishing, cycling, walking/jogging), Status of riverfront spaces (parks, playgrounds, sports fields), Annual cultural festivals, Number of rivers designated among the “100 Beautiful Rivers of Korea,” Status of ecological landscape conservation areas, and Number of designated cultural heritage sites by watershed.

The results of this study are significant in that they demonstrate how the quantification of river ecosystem services can move beyond academic discourse to serve as a practical basis for policy and management decision-making. The indicator system proposed here is particularly meaningful because it is directly linked to official statistical data, thereby complementing the limitations of traditional non-market valuation methods. As such, the system can be employed as a decision-making tool across multiple domains, including national and local water management policies, feasibility assessments of restoration projects, and the prioritization of financial investments. Based on the findings of this study, several recommendations can be made for sustainable river management in the era of the climate crisis. First, it is essential to integrate river ecosystem service indicators into national water resource management frameworks to strengthen climate resilience. Establishing a comprehensive monitoring system using the proposed indicators would enable early detection of ecosystem degradation and help policymakers respond more effectively to flood and drought risks. Second, interdisciplinary collaboration among hydrology, ecology, and spatial planning experts should be institutionalized to enhance the adaptive capacity of river management systems. Third, policy efforts should focus on linking ecosystem service assessments with disaster risk reduction and restoration investment plans to ensure that ecological functions, such as water regulation and flood mitigation, are embedded in long-term water management strategies.

Nevertheless, several limitations remain. First, while the study compared the relative importance of indicators across categories, it did not conduct detailed comparative assessments among single-indicator candidate groups. Second, the analysis relied exclusively on experts, and thus the perceptions of the general public and other stakeholders were not reflected. Future research should therefore incorporate in-depth expert validation procedures such as Focus Group Interviews (FGI) and participatory surveys involving citizens to strengthen the representativeness and interpretability of the indicators. Third, the pool of candidate indicators was primarily derived from a limited number of major international and national reports (e.g., INCA, Water Europe, European Commission, KEI). Although these sources are authoritative and relevant, this may restrict the comprehensiveness of the indicator set. Future studies should therefore expand the literature base and incorporate a wider range of case studies and empirical data to refine and validate the indicators. In conclusion, this study systematically derived indicators for the quantitative evaluation of river ecosystem services using AHP and CVR analyses and proposed an indicator system aligned with international standards. The study thereby makes both academic and policy contributions. These indicators can provide a sound basis for river management, restoration, and sustainable water management strategies, while also contributing internationally to the institutionalization and standardization of ecosystem service valuation.