Climate change drives low dissolved oxygen and increased hypoxia rates in rivers worldwide – Nature

Report on Global River Deoxygenation and its Impact on Sustainable Development

1.0 Introduction

This report summarizes the findings of a global analysis on the trends of dissolved oxygen (DO) concentrations in rivers. The study highlights the profound impact of climate change on freshwater ecosystems, directly challenging the achievement of several key Sustainable Development Goals (SDGs). Rising water temperatures are projected to cause significant decreases in DO, leading to an increase in hypoxia (low oxygen conditions). This phenomenon poses a major, yet previously unquantified, threat to aquatic biodiversity and the health of global river systems, which are critical for sustainable development.

2.0 Methodology

A comprehensive analysis was conducted to assess historical and future trends in riverine dissolved oxygen worldwide. The methodology is characterized by the following:

1. Modeling Approach: A hybrid model combining process-based principles and machine learning techniques was developed and applied.
2. Data Foundation: The model was trained on an extensive dataset comprising approximately 2.6 million global observations of dissolved oxygen.
3. Temporal Scope: The analysis covered two distinct periods:
   • A historical analysis from 1980 to 2019.
   • A future projection from 2020 to 2100, assessing the impact of ongoing global change.

3.0 Key Findings

The model projects a critical and widespread decline in the health of freshwater ecosystems, with significant implications for global sustainability efforts.

• Decreasing Dissolved Oxygen: A significant decreasing trend in dissolved oxygen concentrations is projected for the majority of the world’s rivers through to the year 2100.
• Increased Hypoxia: The decline in DO is expected to result in a substantial increase in the frequency of hypoxic events.
• Quantified Threat: Globally, the model projects an average increase of 8.8 ± 2.3 hypoxia days per decade between 2020 and 2100.
• Ecosystem Threat: These findings indicate a major and escalating threat to the viability of freshwater ecosystems and the biodiversity they support worldwide.

4.0 Implications for Sustainable Development Goals (SDGs)

The projected increase in river hypoxia directly undermines progress towards several SDGs. The degradation of freshwater quality and ecosystems has cascading effects on environmental stability, human well-being, and economic development.

4.1 SDG 6: Clean Water and Sanitation

• Target 6.3 (Improve Water Quality): The widespread decrease in dissolved oxygen represents a severe degradation of water quality. This trend runs counter to the goal of reducing pollution and increasing the proportion of safely treated water bodies.
• Ecosystem Health: Healthy aquatic ecosystems are fundamental to the water cycle and natural purification processes. Increased hypoxia compromises these essential ecosystem services, jeopardizing water security.

4.2 SDG 13: Climate Action

• Direct Impact of Climate Change: This study provides clear evidence of the tangible impacts of climate change (via increased water temperatures) on vital Earth systems.
• Urgency for Mitigation: The findings underscore the urgent need for robust climate action to limit global warming, as failure to do so will directly accelerate the degradation of global freshwater resources.

4.3 SDG 14 (Life Below Water) & SDG 15 (Life on Land)

• Target 15.1 (Conserve Freshwater Ecosystems): The projected increase in hypoxia days poses a direct threat to the conservation and restoration of freshwater ecosystems. Hypoxia leads to “dead zones” incapable of supporting most aquatic life.
• Biodiversity Loss: The decline in dissolved oxygen is a primary driver of fish kills and the loss of aquatic biodiversity, directly impacting the goals related to halting biodiversity loss and protecting vulnerable species.

5.0 Conclusion

The global decline in riverine dissolved oxygen driven by climate change is a critical environmental challenge that directly threatens the foundations of sustainable development. The projected increase in hypoxia will degrade water quality (SDG 6), threaten freshwater biodiversity (SDG 15), and serves as a stark indicator of the consequences of insufficient climate action (SDG 13). Addressing this issue requires an integrated approach that combines aggressive climate change mitigation with enhanced water resource management to protect the world’s vital freshwater ecosystems for future generations.

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

SDG 6: Clean Water and Sanitation

The article directly addresses SDG 6 by focusing on the quality of freshwater resources. It analyzes “trends in dissolved oxygen concentrations” in rivers worldwide, a key parameter of water quality. The projection of “significant decreasing trends in dissolved oxygen” and an “increase in the number of days with hypoxia” highlights a major threat to the health of these water bodies, which is central to ensuring clean water and sanitation.

SDG 13: Climate Action

The article establishes a clear link between climate change and water quality degradation. The opening sentence states, “Increased water temperatures under climate change will probably cause decreases in dissolved oxygen.” This identifies climate change as the primary driver of the problem, making the research highly relevant to understanding the impacts of climate change and the need for urgent action as outlined in SDG 13.

SDG 15: Life on Land

SDG 15 aims to protect, restore, and promote the sustainable use of terrestrial and inland freshwater ecosystems. The article’s conclusion that decreasing dissolved oxygen and increasing hypoxia represent a “major threat to freshwater ecosystems worldwide” directly relates to this goal. Hypoxia has severe consequences for aquatic life, thus impacting the biodiversity and health of these ecosystems, which are a core component of SDG 15.

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

SDG 6: Clean Water and Sanitation

1. Target 6.3: By 2030, improve water quality by reducing pollution. The article’s focus on the decline in “dissolved oxygen concentrations” and the rise of “hypoxia” directly relates to deteriorating water quality. The study provides a global analysis of this degradation, which is a critical aspect of monitoring progress toward this target.
2. Target 6.6: By 2020, protect and restore water-related ecosystems. The research underscores the urgency of this target by quantifying a “major threat to freshwater ecosystems worldwide.” The projected increase in hypoxia days serves as a metric for the degradation of these ecosystems, reinforcing the need for protective and restorative measures.

SDG 13: Climate Action

1. Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards. The article identifies a specific climate-related hazard: the degradation of river water quality due to rising temperatures. The findings highlight the vulnerability of freshwater ecosystems and the need to build resilience against these impacts.

SDG 15: Life on Land

1. Target 15.1: By 2020, ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems. The article’s analysis of a global threat to “freshwater ecosystems” directly aligns with the conservation and restoration goals of this target. The study provides evidence of the negative impacts that undermine the health and sustainability of these vital ecosystems.
2. Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats and halt the loss of biodiversity. The increase in hypoxia is a direct cause of habitat degradation for aquatic species. The article’s findings imply a significant threat to freshwater biodiversity, which depends on adequate dissolved oxygen levels for survival, making this target highly relevant.

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

Yes, the article mentions and implies several specific, measurable indicators that can be used to track progress towards the identified targets, even if it does not use the official SDG indicator codes.

Indicators for SDG 6 Targets

• Indicator for Target 6.3 (Improve water quality): The article uses “dissolved oxygen concentrations” as a primary metric for water quality. The “significant decreasing trends in dissolved oxygen” it projects is a direct measure of water quality degradation. This aligns with the official indicator 6.3.2 (Proportion of bodies of water with good ambient water quality).
• Indicator for Target 6.6 (Protect and restore water-related ecosystems): The “number of days with stress and hypoxia in rivers” is a quantifiable indicator of the health and degradation of freshwater ecosystems. An increase in these days signifies a failure to protect these ecosystems.

Indicators for SDG 13 Targets

• Indicator for Target 13.1 (Strengthen resilience): The article provides a specific, forward-looking indicator of a climate-related hazard: the projected increase of “on average 8.8 ± 2.3 more hypoxia days per decade globally between the years 2020 and 2100.” This metric can be used to assess the growing risk and the need for adaptive measures.

Indicators for SDG 15 Targets

• Indicator for Target 15.1 and 15.5 (Conserve freshwater ecosystems and halt biodiversity loss): The “trends in dissolved oxygen concentrations” and the “number of days with hypoxia” serve as powerful proxy indicators for the health of freshwater habitats. These metrics directly reflect the viability of these ecosystems for supporting aquatic life and biodiversity. A negative trend indicates habitat degradation and an increased threat to species.

4. Create a table with three columns titled ‘SDGs, Targets and Indicators” to present the findings from analyzing the article. In this table, list the Sustainable Development Goals (SDGs), their corresponding targets, and the specific indicators identified in the article.

Source: nature.com