Constructed wetlands (CWs) are widely implemented as nature-based solutions for delivering essential ecosystem services such as water purification, carbon sequestration, and habitat provision. However, biodiversity monitoring within CWs remains limited and unevenly integrated into performance evaluations. This scoping review analyzed 76 peer-reviewed studies to assess current methods for biodiversity monitoring, explore linkages to ecosystem functions, and examine the diversity indices most frequently applied. Results revealed a predominant focus on microbial communities, primarily assessed through high-throughput sequencing and general ecological indices such as the Shannon–Wiener Diversity Index and Chao1 Richness Estimator, with limited taxonomic depth or functional specificity. Plant and animal biodiversity were addressed less frequently and were rarely linked to treatment outcomes or ecosystem services beyond regulation. Vertical subsurface flow systems were the most studied configuration, particularly in lab-scale studies, while free water surface systems exhibited greater microbial phylum richness. These findings highlight a critical need for CW-specific biodiversity monitoring frameworks that integrate microbial, plant, and faunal assessments using functionally relevant phylogenetic indices such as Rao’s Quadratic Entropy and Faith’s Phylogenetic Diversity. Emphasis on standardization, trait-based analyses, and mechanistic approaches is essential for enhancing ecological interpretation and ensuring biodiversity is recognized as a central component of CW design, performance, and resilience.

Constructed wetlands (CWs) are nature-based solutions that integrate ecological processes for water purification, climate regulation, and biodiversity enhancement. However, biodiversity monitoring in CWs has often been underprioritized, limiting its recognition as a functional driver of ecosystem service performance. This study first developed the Biodiversity-based Ecosystem Service Index (BBESI), a hierarchical framework for evaluating biodiversity contributions to regulating services, and then systematically identified representative indicators from the literature to operationalize this framework. Following PRISMA 2020 guidelines, 39 studies spanning tropical, temperate, and arid climatic regions were reviewed across six ecosystem functions: pollutant removal, nutrient retention, biological uptake, carbon storage, greenhouse gas regulation, and microclimate control. Indicators were considered representative when they demonstrated clear functional relevance to CW ecosystem processes and were repeatedly supported across the reviewed studies. These included microbial diversity metrics, nutrient-cycling functional genes, plant–microbe functional complementarity, and vegetation structural attributes. Each indicator was mapped to the Essential Biodiversity Variables (EBV) framework, spanning Genetic Composition, Species Traits, Community Composition, Ecosystem Structure, and Ecosystem Function to provide a standardized basis for biodiversity assessment, using a rule-based assignment that prioritized the biological signal of each indicator rather than its functional category. Although all EBV classes were represented, this pattern reflects the available literature and is influenced by uneven reporting across microbial and plant indicators and across climatic regions, which limits broad generalization of indicator strength. The BBESI offers a transferable framework because its EBV-aligned structure and commonly measured indicators allow application across diverse CW designs and environmental contexts provided that multiple EBV co-signals are present rather than reliance on single-indicator measurements, with flexibility for future integration of various quantitative weighting approaches.

Constructed wetlands (CWs) are multifunctional nature-based solutions whose regulating functions are strongly mediated by microbial communities, yet microbial biodiversity is rarely integrated systematically into ecosystem-function assessment. This study operationalized a Biodiversity-Based Regulating Service Framework in a sequential CW system in South Korea using 16S rRNA gene amplicon sequencing for descriptive microbial characterization and shotgun metagenomics, an untargeted approach for sequencing community DNA, for index construction. Microbial alpha diversity, taxonomic composition, process-associated taxa, and functional genes were integrated into three Biodiversity-Based Regulating Service Indices (BBRSIs) representing pollutant removal (BBRSI-PR), nutrient retention (BBRSI-NR), and carbon-related processes (BBRSI-CS). Spatial and temporal variation was evaluated across October 2025, December 2025, and March 2026. BBRSI-PR and BBRSI-NR showed pronounced spatial differentiation in October but became higher and more uniform by March, whereas BBRSI-CS exhibited a distinct temporal pattern. BBRSI-PR and BBRSI-NR were strongly correlated (r = 0.99, p < 0.0001), while both showed weaker positive relationships with BBRSI-CS. Process-associated taxa exhibited greater spatial and temporal variability than several corresponding functional-gene groups. Overall, the framework integrated structural and functional microbial evidence into function-specific indicators capable of revealing internal heterogeneity and temporal change not apparent from inlet–outlet water-quality patterns alone.