Terrestrial land cover shapes fish diversity in a major subtropical river catchment – Nature

 

Report on Terrestrial Land Cover Impacts on Freshwater Fish Diversity and the Sustainable Development Goals

Executive Summary

This report details the findings of a study on the impacts of terrestrial Land Use and Land Cover (LULC) on freshwater fish biodiversity in Thailand’s Chao Phraya River catchment. The research demonstrates a critical link between land-based human activities and the health of aquatic ecosystems, providing vital insights for achieving the Sustainable Development Goals (SDGs), particularly SDG 14 (Life Below Water), SDG 15 (Life on Land), and SDG 6 (Clean Water and Sanitation). Using environmental DNA (eDNA) and a novel spatial model, the study quantifies how different land uses—such as agriculture, forestry, and urbanization—affect fish species richness. Key findings indicate that LULC impacts extend up to 20 km upstream and that while agricultural expansion may increase overall fish numbers, it simultaneously threatens species of conservation concern, leading to a net loss of unique biodiversity (biotic homogenization). These results underscore the urgent need for integrated land and water management policies that consider cross-ecosystem impacts to balance development goals like SDG 2 (Zero Hunger) and SDG 11 (Sustainable Cities and Communities) with essential conservation targets.

Introduction: Aligning Biodiversity Conservation with Sustainable Development Goals

The Challenge: Land Use and its Impact on SDG 14 and SDG 15

The global decline in biodiversity presents a significant obstacle to the 2030 Agenda for Sustainable Development. Freshwater ecosystems, which are hotspots of biodiversity, are disproportionately threatened by human activities. The modification of terrestrial landscapes is a primary driver of this threat, creating complex challenges for policymakers.

• Impact on SDG 14 (Life Below Water): Alterations in land cover, driven by agriculture and urban expansion, directly affect water quality, habitat structure, and resource availability in rivers, leading to declines in fish populations and threatening aquatic ecosystems.
• Impact on SDG 15 (Life on Land): The conversion of forests and natural habitats to croplands and urban areas degrades terrestrial ecosystems, which are intrinsically linked to the health of adjacent river systems through resource and pollution flows.
• Interlinked Goals: Activities supporting SDG 2 (Zero Hunger) through agricultural intensification and SDG 11 (Sustainable Cities) through urban growth often have unintended negative consequences for biodiversity and water quality (SDG 6), undermining progress on SDG 14 and SDG 15.

A significant knowledge gap exists regarding the precise spatial scale and magnitude of these land-water linkages. This uncertainty impedes the development of effective, evidence-based management strategies required to achieve the SDGs.

Study Focus: The Chao Phraya Catchment

The study was conducted in the 160,000-km² Chao Phraya River catchment in Thailand. This subtropical region is a global biodiversity hotspot but faces intense pressure from anthropogenic alterations, including centuries of agricultural expansion and rapid urbanization. This setting provides a critical case study for understanding the trade-offs between development and conservation in highly diverse, data-deficient tropical regions.

Methodology: An Integrated Approach for Sustainable Management

Data Collection and Analysis

To overcome traditional data limitations, this study employed a modern, spatially explicit approach to provide a scalable model for monitoring and managing riverine ecosystems in line with SDG targets.

1. Fish Diversity Assessment: Fish communities were surveyed at 39 sites across the catchment using environmental DNA (eDNA) metabarcoding. This non-invasive technique efficiently captures a comprehensive snapshot of local species richness, including threatened and rare species.
2. Land Use and Land Cover (LULC) Quantification: High-resolution satellite data (ESA CCI) was used to map contemporary LULC. The landscape was classified into five predominant types: rainfed cropland, irrigated cropland, forest, shrub- and grassland, and urban areas.
3. Spatially Explicit Modeling: A novel model (FishDiv-LULC) was developed to link fish species richness to the various LULC types within the upstream catchment area of each sampling site, accounting for the decay of influence over distance.

Key Findings: Linking Land Use to Aquatic Biodiversity Outcomes

Quantifying the Impact of Land Use on Fish Diversity

The model successfully quantified the relationship between terrestrial land use and riverine fish diversity, explaining nearly 60% of the observed variance in species richness. The findings provide a clear spatial and quantitative basis for land management decisions.

• Spatial Range of Impact: Terrestrial LULC effects on local fish communities were found to extend up to a significant distance of approximately 19 km upstream from a given point in the river.
• Impact of Croplands: Rainfed cropland was associated with a relative increase in overall fish species richness. This is likely due to nutrient runoff acting as a subsidy, favoring adaptable, generalist species. This highlights a critical trade-off between agricultural productivity (SDG 2) and the integrity of aquatic ecosystems (SDG 14).
• Impact of Forests and Urban Areas: In contrast, forest and urban areas were associated with a relative decrease in species richness compared to the baseline. Forests harbor distinct, specialized communities, while urban areas introduce pollution and habitat degradation, negatively impacting most species and challenging the goals of SDG 11 and SDG 6.

Implications for Species of Conservation Concern

A critical insight from the study is that an increase in overall species richness does not necessarily indicate a healthy ecosystem. The analysis revealed that land use changes favoring generalist species come at the expense of vulnerable and specialized ones.

• Threatened Species: The conversion of natural habitats like forests to croplands was projected to cause a decline in the richness of fish species of conservation concern (SPCC), as defined by the IUCN Red List.
• Biotic Homogenization: This trend suggests that ongoing LULC change promotes the homogenization of fish communities, where unique, locally-adapted species are replaced by a few widespread, human-tolerant species. This represents a significant loss of biodiversity and a failure to meet the targets of SDG 15.5, which calls for halting biodiversity loss and preventing the extinction of threatened species.

Projections and Scenarios: Forecasting Progress Towards the 2030 Agenda

Historical and Future Land Use Change Scenarios

The model was used to project fish diversity patterns based on historical (1992-2016) and future (2016-2050) LULC scenarios. Future projections under different Shared Socio-economic Pathways (SSPs) show an acceleration of trends that threaten biodiversity.

• Past Trends: From 1992 to 2016, urban areas expanded by nearly 300%, primarily along major river channels.
• Future Projections: Under a business-as-usual scenario (SSP5 RCP8.5), croplands are forecast to increase by 25% and forests to decrease by 26% by 2050, particularly in hilly and mountainous regions that currently serve as refuges for biodiversity.

Divergent Futures for Overall vs. Threatened Biodiversity

The projections reveal a starkly different future for generalist species versus those requiring conservation. While the expansion of agriculture into forested regions is predicted to increase overall fish species richness in those areas, this comes at a high cost. The loss of forest cover is predicted to lead to a significant decline in the habitats available for SPCCs, pushing them closer to extinction and further undermining the objectives of SDG 14 and SDG 15.

Conclusions and Recommendations for Policy and Management

Key Takeaways for Sustainable Land and Water Management

This research provides a powerful demonstration that sustainable development requires a holistic, cross-ecosystem approach. The key takeaways are:

• Terrestrial land management is inseparable from freshwater conservation.
• The impacts of land use are spatially explicit and can be modeled to inform better planning.
• Biodiversity metrics must look beyond simple species counts to account for the loss of unique and threatened species.
• The integrated eDNA and modeling framework is a cost-effective, scalable tool for monitoring progress towards the SDGs in other global catchments.

Recommendations for Achieving Sustainable Development Goals

To mitigate biodiversity loss and achieve the 2030 Agenda, the following actions are recommended:

1. Integrate Land and Water Policies: National and regional policies must explicitly address the trade-offs between agriculture (SDG 2), urban development (SDG 11), and the conservation of aquatic and terrestrial ecosystems (SDG 14, SDG 15).
2. Implement Spatially-Aware Conservation: Conservation initiatives like the ’30 by 30′ target should incorporate spatial data on LULC impacts. The identified 19 km effective range should inform the design of riparian buffer zones and protected area networks.
3. Promote Sustainable Land Use: Incentivize agricultural practices that minimize nutrient runoff and protect soil health. Urban planning must include green infrastructure and advanced wastewater treatment to reduce pollution entering rivers, supporting SDG 6 and SDG 11.
4. Prioritize Protection of Natural Habitats: Protect remaining forests, particularly in headwater regions, as they are critical refuges for threatened species and essential for maintaining the ecological integrity of the entire river catchment (SDG 15.1).
5. Adopt Advanced Monitoring Techniques: Encourage the use of eDNA and remote sensing to provide the timely, large-scale data needed to track LULC changes and their biodiversity impacts, enabling adaptive management and accountability for SDG commitments.

1. SDGs Addressed in the Article

SDG 15: Life on Land

This is the most central SDG to the article. The study directly investigates the impact of terrestrial land use and land cover (LULC) changes on freshwater biodiversity. It focuses on how the degradation of terrestrial habitats like forests and the expansion of agriculture and urban areas directly affect life in adjacent river ecosystems, which are inland freshwater ecosystems explicitly covered by this goal. The article states, “Freshwater biodiversity is critically affected by human modifications of terrestrial land use and land cover (LULC)” and aims to provide a “scalable basis for riverine biodiversity conservation and land management.”

SDG 14: Life Below Water

While primarily focused on marine environments, the principles of SDG 14 are highly relevant. The article’s core subject is the conservation of aquatic biodiversity, specifically “fish diversity,” “fish species richness,” and “threatened species.” The study’s examination of how land-based human activities (LULC changes, pollution) degrade aquatic habitats and threaten fish populations aligns with the goal’s broader objective of conserving and sustainably using aquatic ecosystems.

SDG 6: Clean Water and Sanitation

The article connects LULC changes to water quality, which is a core component of SDG 6. It discusses how different land uses affect riverine habitats, mentioning “nutrient run-offs from the surrounding terrestrial land” in agricultural areas and “wastewater and chemical pollution” associated with urban areas. By analyzing these impacts, the study implicitly addresses the need to protect and restore water-related ecosystems and improve water quality by reducing pollution from land-based activities.

SDG 11: Sustainable Cities and Communities

The article highlights the negative impact of urbanization on riverine biodiversity. It notes that “urban areas have also expanded rapidly in recent decades” and that they have a “relative negative” effect on fish species richness due to “high anthropogenic disturbances.” This directly relates to the challenge of making urban expansion sustainable and mitigating its environmental impact on surrounding ecosystems.

2. Specific Targets Identified

Targets under SDG 15 (Life on Land)

• Target 15.1: By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services, in particular forests, wetlands, mountains and drylands, in line with obligations under international agreements.
  
  Explanation: The entire study is an analysis of the linkage between terrestrial ecosystems (forests, croplands) and “inland freshwater ecosystems” (the Chao Phraya river catchment). Its goal of creating a model to “offer a scalable basis for riverine biodiversity conservation and land management” directly supports the sustainable use and conservation of these ecosystems.
• Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species.
  
  Explanation: The article directly addresses this target by quantifying biodiversity loss (“future gains and losses of fish species richness”) and focusing specifically on threatened species. It identifies seven “critically endangered (CR), endangered (EN), vulnerable (VU), or near threatened (NT)” species, analyzes their decline, and states that “native and often endangered species associated with natural habitats could be replaced.”
• Target 15.9: By 2020, integrate ecosystem and biodiversity values into national and local planning, development processes, poverty reduction strategies and accounts.
  
  Explanation: The research develops a “spatially explicit model” intended as a tool for policy and planning. The article concludes that its approach gives “scientists and stakeholders a potent tool in land management and conservation area design,” which is the essence of integrating biodiversity values into planning.

Targets under SDG 6 (Clean Water and Sanitation)

• Target 6.3: By 2030, improve water quality by reducing pollution, eliminating dumping and minimizing release of hazardous chemicals and materials, halving the proportion of untreated wastewater and substantially increasing recycling and safe reuse globally.
  
  Explanation: The article links LULC types to water quality degradation. It discusses how “rivers near croplands received high nutrient run-offs” and how “contemporary wastewater and chemical pollution and high anthropogenic disturbances associated with urban areas affect fish assemblage structure.” This analysis supports the scientific basis for actions needed to reduce such pollution.
• Target 6.6: By 2020, protect and restore water-related ecosystems, including mountains, forests, wetlands, rivers, aquifers and lakes.
  
  Explanation: The study’s focus is on understanding the threats to a major river catchment to “allow for potential mitigation of biodiversity loss.” By modeling the impacts of LULC, it provides a direct method for assessing the health of the river ecosystem and identifying areas needing protection and restoration.

3. Indicators Mentioned or Implied

Biodiversity and Ecosystem Health Indicators

• Fish Species Richness: This is the primary metric used throughout the article to quantify biodiversity. The study “explained nearly 60% of the variance in the observed species richness” and projected “future gains and losses of fish species richness.” This serves as a direct indicator of ecosystem health.
• Richness of Species of Conservation Concern (SPCC): The article specifically tracks a subset of species based on the “Red List of the International Union for Conservation of Nature (IUCN).” By projecting changes for these seven threatened species, it provides a direct indicator for progress on preventing extinctions (relevant to Target 15.5).
• Jaccard Similarity Index: The article mentions using this index to measure the “uniqueness of fish species across the catchment.” A decrease in uniqueness (homogenization) is an indicator of biodiversity loss, showing that even if overall richness increases, the diversity of specialist species may be declining.

Land Use and Water Quality Indicators

• Land Use and Land Cover (LULC) Change: The study quantifies the percentage of land covered by different types (croplands, forest, urban). It tracks historical changes (e.g., “urban areas increased by 295% from 1992 to 2016”) and projects future changes, which serves as an indicator of habitat degradation and pressure on ecosystems. This is directly related to Indicator 15.1.1 (Forest area as a proportion of total land area).
• Water Quality Parameters (Chlorophyll-a, TSS, DOC): The article explicitly measures “river chlorophyll-a content (Chl-a), total suspended solids (TSS), and dissolved organic carbon (DOC)” using remote sensing data. These are used as direct indicators of “nutrient availability and productivity” and pollution from different land uses, which is relevant for measuring water quality (Target 6.3).

4. Table of SDGs, Targets, and Indicators

SDGs	Targets	Indicators
SDG 15: Life on Land	15.1: Ensure conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems. 15.5: Halt biodiversity loss and protect threatened species. 15.9: Integrate ecosystem and biodiversity values into planning.	– Fish Species Richness – Richness of Species of Conservation Concern (SPCC) based on IUCN Red List status – Jaccard Similarity Index (to measure community uniqueness) – Percentage of land cover change (forest, cropland, urban)
SDG 6: Clean Water and Sanitation	6.3: Improve water quality by reducing pollution. 6.6: Protect and restore water-related ecosystems.	– Water quality parameters: Chlorophyll-a (Chl-a), Total Suspended Solids (TSS), Dissolved Organic Carbon (DOC) – Fish species richness as a bio-indicator of ecosystem health
SDG 14: Life Below Water	14.2: Sustainably manage and protect marine and coastal ecosystems (applied by analogy to freshwater ecosystems).	– Fish species richness and community composition – Status of threatened fish species
SDG 11: Sustainable Cities and Communities	11.3: Enhance inclusive and sustainable urbanization.	– Percentage increase in urban area coverage – Modeled negative impact of urban areas on fish species richness

Source: nature.com