Taxonomic and functional responses of stream macroinvertebrates across different land use types – Nature

Executive Summary

This report details an investigation into the impacts of urbanization and agricultural expansion on freshwater biodiversity, with a direct focus on its implications for achieving the United Nations Sustainable Development Goals (SDGs). A comparative analysis of benthic macroinvertebrate communities was conducted across 121 stream sites in South Korea, categorized by dominant land use: forest, agriculture, and urban. The findings reveal a significant decline in taxonomic richness in streams affected by human activity, directly challenging the objectives of SDG 15 (Life on Land). Conversely, functional divergence increased in urban and agricultural streams, indicating that surviving species develop specialized traits to cope with environmental stressors like pollution and habitat degradation. This specialization suggests a loss of ecosystem resilience, which compromises progress towards SDG 6 (Clean Water and Sanitation) and SDG 11 (Sustainable Cities and Communities). The dominance of pollution-tolerant species such as Asellus sp. in disturbed areas serves as a clear bioindicator of ecosystem degradation. This study concludes that incorporating functional diversity metrics alongside traditional taxonomic assessments is essential for developing effective conservation strategies and accurately monitoring progress toward global biodiversity and sustainability targets.

1.0 Introduction: Aligning Freshwater Biodiversity with Sustainable Development Goals

1.1 The Global Biodiversity Crisis and SDG 15

The unprecedented decline in freshwater biodiversity represents a critical obstacle to achieving SDG 15 (Life on Land), which explicitly calls for halting biodiversity loss. Freshwater ecosystems are degrading more rapidly than their terrestrial or marine counterparts, primarily due to anthropogenic pressures. The principal drivers of this loss include:

• Changes in land use (urbanization and agriculture)
• Pollution
• Climate change
• Overexploitation
• Invasive alien species

This report focuses on land-use change, a primary factor undermining the ecological integrity required to meet the targets of SDG 15.

1.2 Land-Use Change as a Barrier to SDG 6 and SDG 11

Urbanization and agricultural expansion directly degrade freshwater habitats, leading to consequences that threaten other key SDGs. These land-use changes result in:

• Water Quality Degradation: Increased nutrient and pollutant runoff from urban and agricultural areas compromises efforts to ensure clean water, a core target of SDG 6 (Clean Water and Sanitation).
• Habitat Fragmentation: The physical alteration of river systems fragments habitats, reducing their capacity to support diverse life and provide essential ecosystem services.
• Threats to Urban Resilience: For SDG 11 (Sustainable Cities and Communities), the health of urban waterways is integral to creating resilient and sustainable urban environments. Degraded streams diminish the quality of life and ecological stability in cities.

1.3 Study Objectives in the Context of Sustainable Development

This study utilizes benthic macroinvertebrates as bioindicators to assess the health of freshwater ecosystems under different land-use pressures. The primary objective is to compare both taxonomic and functional diversity to provide a comprehensive understanding of ecosystem response to disturbance. By analyzing how functional traits within a community shift, this research offers deeper insights into ecosystem functionality and resilience, providing critical data for:

1. Developing effective conservation strategies aligned with SDG 15.
2. Informing land-use planning and water management policies that support SDG 6 and SDG 11.
3. Advocating for the integration of functional diversity metrics into national and global biodiversity monitoring frameworks.

2.0 Research Findings: Land-Use Impacts on Aquatic Ecosystems

2.1 Taxonomic and Functional Diversity Metrics

The analysis of 84,343 macroinvertebrates from 121 stream sites revealed distinct patterns linked to land use, highlighting the challenges in meeting biodiversity targets under SDG 15.

• Taxonomic Diversity: Species richness was significantly highest in pristine forest streams (23.3 taxa on average) and lowest in urban streams (7.9 taxa). This stark decline in species numbers in human-altered landscapes demonstrates a direct loss of biodiversity.
• Functional Richness (Fric): The range of functional traits was highest in forest streams and lowest in urban streams, indicating that urban ecosystems support a narrower range of ecological roles, making them less resilient.
• Functional Divergence (Fdiv): Conversely, functional divergence was significantly higher in agricultural and urban streams. This indicates that the few species that survive in these stressful environments are highly specialized, occupying distinct niches to avoid competition. This specialization, however, points to a fragile ecosystem with low functional redundancy.

2.2 Community Composition and Dissimilarity Across Land-Use Gradients

The composition of macroinvertebrate communities differed significantly across the three land-use types, both taxonomically and functionally. The greatest dissimilarity was observed between forest and urban streams, underscoring the profound ecological transformation caused by urbanization. This transformation directly impacts the health of aquatic ecosystems, a key concern for SDG 14 (Life Below Water) and SDG 15. Environmental factors associated with unsustainable land use were strongly correlated with these community shifts:

• Urban Streams: Community structure was strongly influenced by high water temperature and conductivity, indicators of thermal pollution and runoff that contravene the principles of SDG 11.
• Agricultural Streams: The presence of burrowing species adapted to sedimentation reflects the impact of agricultural runoff, a key challenge for achieving sustainable food production under SDG 12 (Responsible Consumption and Production).
• Forest Streams: High biodiversity was associated with pristine conditions, demonstrating the importance of protected areas for conserving life on land and in water.

2.3 Indicator Species and Traits as Bioindicators for SDG Monitoring

Specific species and functional traits served as powerful indicators of ecosystem health, providing a practical tool for monitoring progress towards environmental SDGs.

• Urban Indicators: The dominance of pollution-tolerant species like Asellus sp. (known for its tolerance to low oxygen) and predators like Alboglossiphonia heteroclita points to degraded water quality and simplified food webs, signaling poor progress on SDG 6. Traits such as strong exoskeletons and parasitic feeding strategies were also indicative of highly disturbed urban environments.
• Agricultural Indicators: Species adapted to sediment-rich substrates, such as Limnodrilus gotoi and Chironomidae, were prevalent. The dominance of collector-gatherers and larger species indicates nutrient enrichment from agricultural runoff.
• Forest Indicators: A total of 51 taxa, including sensitive species like Epeorus pellucidus, were indicators of healthy forest streams. Their associated traits—such as gill respiration and clinging ability—are adapted to clean, fast-flowing, oxygen-rich water, representing the baseline conditions that SDG-focused restoration efforts should target.

3.0 Discussion: Implications for SDG Implementation and Policy

3.1 Trait Specialization as an Adaptive Response to Environmental Stressors

The finding that functional divergence increases in disturbed streams, despite a sharp drop in species richness, is critical for understanding ecosystem stability. This trait reorganization reflects an adaptive response where communities become dominated by a few highly specialized species. While this allows some ecological functions to persist, it signifies a loss of functional redundancy and resilience. Such fragile ecosystems are more vulnerable to further shocks, such as climate change or extreme weather events, undermining the goal of building resilient communities and ecosystems as envisioned in SDG 11 and SDG 15.

3.2 Indicator Species and Ecosystem Health in Relation to SDGs

The distinct indicator species and traits identified for each land-use type provide a clear narrative of ecological degradation.

• In urban and agricultural streams, the dominant traits are those of survival and tolerance to pollution, sedimentation, and habitat simplification. This reflects a failure to manage land use sustainably, directly impeding the achievement of SDG 6, SDG 11, SDG 12, and SDG 15.
• In contrast, the diverse functional traits in forest streams—including various feeding strategies and life cycles—highlight the complexity and health of intact ecosystems. These streams serve as crucial benchmarks for restoration efforts and demonstrate the value of conservation in achieving global sustainability targets.

3.3 Integrating Functional Diversity into Biodiversity Frameworks

This study demonstrates that relying solely on taxonomic metrics, such as species richness, provides an incomplete picture of biodiversity loss. Functional diversity metrics offer a more nuanced understanding of how ecosystems respond to anthropogenic pressures. For global frameworks like the Kunming-Montreal Global Biodiversity Framework, which supports SDG 15, integrating trait-based indicators is essential. Such an approach would allow policymakers to:

1. Detect early signs of ecosystem degradation before extensive species loss occurs.
2. Assess the functional consequences of biodiversity loss on ecosystem services, such as water purification (SDG 6).
3. Design more effective and targeted conservation and restoration strategies that aim to restore not just species numbers but also critical ecological functions.

4.0 Conclusion and Recommendations

This research confirms that unsustainable urbanization and agricultural expansion severely degrade freshwater biodiversity, creating significant barriers to achieving multiple Sustainable Development Goals, particularly SDG 6, SDG 11, and SDG 15. The loss of taxonomic diversity and the concurrent shift towards functionally specialized communities in disturbed streams highlight a widespread decline in ecosystem health and resilience. To address these challenges and advance the 2030 Agenda for Sustainable Development, the following actions are recommended:

1. Enhance Biodiversity Monitoring: National and international bodies should integrate functional diversity metrics into biodiversity assessment protocols to provide a more comprehensive evaluation of ecosystem health and resilience, thereby improving reporting for SDG 15.
2. Promote Sustainable Land-Use Planning: Municipal and national governments must implement land-use policies that include the protection of riparian buffer zones and the integration of green infrastructure to mitigate the impacts of runoff, directly supporting SDG 6 and SDG 11.
3. Foster Sustainable Agriculture: Policies must incentivize agricultural practices that minimize soil erosion and nutrient runoff, such as cover cropping and precision farming, to protect downstream aquatic ecosystems, aligning with the goals of SDG 12 and SDG 15.
4. Prioritize Ecosystem Restoration: Conservation efforts should focus on restoring not only the taxonomic composition but also the functional diversity of degraded streams to rebuild resilient ecosystems capable of providing essential services.

Analysis of Sustainable Development Goals (SDGs) in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

1. SDG 6: Clean Water and Sanitation
   • The article directly addresses the degradation of freshwater ecosystems, a core component of SDG 6. It highlights how urbanization and agricultural expansion lead to “water quality degradation,” “increased nutrient and pollutant runoff,” and the dominance of pollution-tolerant species in streams. This connects to the goal of ensuring the availability and sustainable management of water.
2. SDG 11: Sustainable Cities and Communities
   • The research identifies “urbanization” as a major driver of freshwater biodiversity loss. By comparing urban stream sites with forest and agricultural ones, the article examines the environmental impact of urban development on aquatic habitats, which is a key concern for making cities sustainable and reducing their ecological footprint.
3. SDG 14: Life Below Water
   • While often associated with marine environments, SDG 14 aims to conserve and sustainably use all aquatic life. The article’s focus on the decline of “freshwater biodiversity,” specifically benthic macroinvertebrates, falls under the purview of protecting aquatic ecosystems from land-based pollution and habitat degradation.
4. SDG 15: Life on Land
   • This goal explicitly includes the protection, restoration, and sustainable use of “inland freshwater ecosystems” and halting biodiversity loss. The article’s central theme—assessing the impact of land-use changes (forest, agriculture, urban) on the taxonomic and functional diversity of stream life—is directly aligned with the objectives of SDG 15.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. Target 6.3: Improve water quality by reducing pollution
   • The article explains that land transformation into urban and agricultural areas results in “increased nutrient and pollutant runoff,” which directly degrades water quality. The study’s findings on pollution-tolerant species like Asellus sp. and Limnodrilus gotoi dominating in urban and agricultural sites underscore the challenge of water pollution addressed by this target.
2. Target 6.6: Protect and restore water-related ecosystems
   • The research provides a clear assessment of the health of different stream ecosystems. It shows that forest streams support high biodiversity, while urban and agricultural streams are degraded. This information is crucial for developing “effective conservation and management strategies to preserve freshwater biodiversity,” which is the essence of Target 6.6.
3. Target 11.6: Reduce the adverse per capita environmental impact of cities
   • The study demonstrates the negative environmental impact of urbanization, noting that “urban streams were dominated by” pollution-tolerant species and had the “lowest” taxonomic richness. This highlights the pressure cities exert on local ecosystems, a problem that Target 11.6 aims to mitigate.
4. Target 15.1: Ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems
   • The article’s comparison of macroinvertebrate diversity across forest, agricultural, and urban streams directly evaluates the state of inland freshwater ecosystems. The high diversity in forest streams serves as a benchmark for conservation, while the degraded state of other streams points to the need for restoration, aligning with this target.
5. Target 15.5: Take urgent action to reduce the degradation of natural habitats and halt the loss of biodiversity
   • The article provides direct evidence of biodiversity loss, stating that “taxonomic richness was highest in forest streams and lowest in urban streams” and “functional richness declined in disturbed streams.” This quantification of biodiversity decline due to land-use changes directly supports the call to action in Target 15.5.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

1. Water Quality Parameters
   • The article explicitly mentions several water quality factors used in the study, such as “dissolved oxygen (DO), biological oxygen demand (BOD), ammonia nitrogen (NH3–N), nitrate nitrogen (NO3–N), total nitrogen (TN), phosphate-phosphorus (PO4–P), total phosphorus (TP), and conductivity.” These serve as direct indicators for measuring water pollution and progress towards Target 6.3.
2. Biodiversity and Ecosystem Health Metrics
   • The study uses various metrics to assess the health of freshwater ecosystems. These include “taxonomic richness,” “Shannon diversity,” “functional richness (Fric),” and “functional divergence (Fdiv).” A change in these metrics over time can indicate progress in protecting and restoring ecosystems (Targets 6.6, 15.1, and 15.5).
3. Indicator Species and Traits
   • The article identifies specific “indicator species” and “indicator traits” for different levels of ecosystem health. For example, the presence of sensitive taxa like Epeorus pellucidus indicates healthy, forested streams, while the dominance of tolerant species like Asellus sp. indicates polluted urban streams. Monitoring the abundance and distribution of these indicator species can serve as a practical tool to assess ecosystem integrity.
4. Land Cover Percentage
   • The methodology classifies study sites based on the percentage of “urban,” “agricultural,” and “forest” land cover. This percentage can be used as an indicator of the pressure on ecosystems from different human activities, relevant for monitoring the impacts of urbanization (Target 11.6) and land-use change (Target 15.5).

4. Summary Table of SDGs, Targets, and Indicators

Source: nature.com