16:25 〜 16:40
[ACG51-10] Mangroves in a Mega City: Insights from Tree-Ring Nitrogen Stable Isotopes
キーワード：人為的活動に起因する汚染、劣化、同位体比分析、マングローブ、ムンバイ、都市化
Mangrove forests, found in brackish waters of tropical and subtropical regions, are among the most diverse and productive ecosystems (Lee et al., 2014). Since the 1970s, their global area has significantly decreased due to human activities such as coastal development (Friess et al., 2019). Recently, deforestation rates have slowed due to conservation efforts like tree planting and regulations (Friess et al., 2019). However, mangrove loss persists in many countries, and future risks, including sea level rise and extreme weather from global warming, may exacerbate degradation. Understanding mangrove growth dynamics under changing environmental conditions is essential for effective conservation.
Mumbai, a megacity of over 20 million people, faces rapid population growth and urban development. Despite the 1991 designation of mangrove forests as protected areas, their environment continues to deteriorate. Long-term monitoring has not been conducted, leaving gaps in understanding degradation timelines and growth patterns. Previous studies have used carbon, oxygen, and nitrogen stable isotopes in tree rings to assess historical pollution impacts, with d15N changes indicating nitrogen uptake from anthropogenic sources (Savard et al., 2010). This study analyzed mangrove tree-ring stable isotopes to identify d15N changes and their timing.
In August 2024, tree-ring samples were collected using an increment borer from Avicennia marina trees on Mumbai's northwestern coast. Samples were stored in glass vials and transported to Japan, where growth layers were separated with a thin knife. Nitrogen and carbon stable isotope ratios were analyzed for each layer. For nitrogen stable analysis, a narrow, high-sensitivity tube was employed, allowing the analysis to be conducted with approximately one-third of the sample quantity required by standard tubes A water quality survey was also conducted to understand the growth environment.
Wood typically has low nitrogen content (<0.1% dry weight; Savard et al., 2010), but the nitrogen content in this study ranged from 0.3% to 0.8%. The average d15N across all growth layers was 10.0 ± 0.7‰, higher than d15N values reported in other tropical tree rings. d15N near the tree core was also close to 10.0‰, indicating that Mumbai mangroves have been exposed to anthropogenic nitrogen pollution since early growth stages. These results align with findings that mangroves can thrive in eutrophic conditions (Erftemeijer et al., 2021).
Nutrient-rich environments may promote above-ground growth but reduce root productivity, potentially diminishing mangroves' carbon storage and coastal protection (Mack et al., 2024). To preserve mangrove ecosystem services, it is crucial to rebuild sustainable relationships between people and mangroves. This requires cooperation among stakeholders. Understanding stakeholder perceptions and identifying conservation actions are key first steps.
Future research will combine environmental data from this study with insights into local perceptions of mangroves in Mumbai. This interdisciplinary approach aims to understand how rapid urbanization has shaped human-mangrove relationships and to identify suitable conservation strategies for Mumbai. At the conference, we hope to discuss this study’s findings, future research, and conservation prospects.
Mumbai, a megacity of over 20 million people, faces rapid population growth and urban development. Despite the 1991 designation of mangrove forests as protected areas, their environment continues to deteriorate. Long-term monitoring has not been conducted, leaving gaps in understanding degradation timelines and growth patterns. Previous studies have used carbon, oxygen, and nitrogen stable isotopes in tree rings to assess historical pollution impacts, with d15N changes indicating nitrogen uptake from anthropogenic sources (Savard et al., 2010). This study analyzed mangrove tree-ring stable isotopes to identify d15N changes and their timing.
In August 2024, tree-ring samples were collected using an increment borer from Avicennia marina trees on Mumbai's northwestern coast. Samples were stored in glass vials and transported to Japan, where growth layers were separated with a thin knife. Nitrogen and carbon stable isotope ratios were analyzed for each layer. For nitrogen stable analysis, a narrow, high-sensitivity tube was employed, allowing the analysis to be conducted with approximately one-third of the sample quantity required by standard tubes A water quality survey was also conducted to understand the growth environment.
Wood typically has low nitrogen content (<0.1% dry weight; Savard et al., 2010), but the nitrogen content in this study ranged from 0.3% to 0.8%. The average d15N across all growth layers was 10.0 ± 0.7‰, higher than d15N values reported in other tropical tree rings. d15N near the tree core was also close to 10.0‰, indicating that Mumbai mangroves have been exposed to anthropogenic nitrogen pollution since early growth stages. These results align with findings that mangroves can thrive in eutrophic conditions (Erftemeijer et al., 2021).
Nutrient-rich environments may promote above-ground growth but reduce root productivity, potentially diminishing mangroves' carbon storage and coastal protection (Mack et al., 2024). To preserve mangrove ecosystem services, it is crucial to rebuild sustainable relationships between people and mangroves. This requires cooperation among stakeholders. Understanding stakeholder perceptions and identifying conservation actions are key first steps.
Future research will combine environmental data from this study with insights into local perceptions of mangroves in Mumbai. This interdisciplinary approach aims to understand how rapid urbanization has shaped human-mangrove relationships and to identify suitable conservation strategies for Mumbai. At the conference, we hope to discuss this study’s findings, future research, and conservation prospects.