Effects of anthropogenic land use on temperate mangrove forests

Coastal ecosystems worldwide are facing unprecedented challenges due to ever increasing human activities, resulting in increased land-derived stressors that can threaten the health and integrity of these systems. Mangrove forests are unique ecosystems that play a crucial role in filtering nutrients, retaining pollutants, and sequestering carbon. However, to what extent they are impacted by an intensification of human pressures is unclear and empirical evidence of landscape scale effects of a holistic view of the ecosystem is scarce. This thesis investigates the effects of human land use on several aspects of temperate mangrove ecosystems and aims to identify potential vulnerabilities of ecosystem processes to provide a holistic view on the impacts that humas are having on these important ecosystems. By working across a broad gradient of human land use, the first chapter establishes a connection between human land use intensity in catchments and regionally generalizable trends in mangrove forest structure and physicochemical parameters in sediments. Highlighting the integrated nature of anthropogenic impacts, this chapter emphasizes the need for holistic evaluations in assessing responses of complex natural systems to change. The second chapter investigates environmental controls on organic matter degradation in mangrove forests. Results from this study emphasize the importance of considering multiple factors influencing degradation processes, that vary with the quality of the decaying organic matter. Furthermore, using the human land use gradient from the previous chapter, this study identifies an impact of human land use through eutrophication on the rate of labile organic matter loss from mangrove sediments. The third chapter provides insights into bacterial communities in temperate mangrove sediments, revealing the persistent effects of nutrient enrichment even after the biochemical signal is lost. The study highlights the spatial resolution needed to detect impacts on microbial communities, warning that functional changes may persist beyond observable eutrophication effects. The synthesis of these chapters provides a holistic view of the effects of anthropogenic impacts on temperate mangrove ecosystems across various scales. While some components of the system may benefit from moderate amounts of nutrient enrichment, others can deteriorate, ultimately diminishing overall service provisioning of the system. To understand and quantify these effects, this thesis calls for a nuanced understanding of disturbance effects on mangrove ecosystems, emphasizing their complexity and the interconnectedness of their components. It adds a valuable information about the functional resilience of mangrove forests in the face of human pressures and highlights the importance of an ecosystem-based perspective when assessing the effects of external stressors on these important ecosystems.

Grantor dc:publisher.institution

The University of Waikato

Year dc:date.issued

2024

Author dc:creator

• Thomson, Timothy

Advisors dc:contributor.advisor

• Ellis, Joanne I.
• Pilditch, Conrad A.
• Cary, S. Craig
• Fusi, Marco

• Temperate mangrove forests
• Avicennia marina
• mangrove expansion
• coastal eutrophication
• sediment biogeochemistry
• marine microbial ecology
• human stressors
• catchment land use
• tea bag index
• organic matter decomposition
• coastal management
• integrated management
• mangrove sediment

Statement dc:rights

• All items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.

Licence

• https://researchcommons.waikato.ac.nz/bitstreams/1d23e0bd-3b83-4496-bbd1-823e96f51993/download