Quantifying the impact of tropical deforestation on coral reefs to support coordinated tropical forest and marine conservation

This project will provide new evidence of the impacts of sediment runoff from tropical deforestation on coral reefs, supporting joined-up conservation of tropical forests and marine ecosystems

The degradation of coral reefs is escalating worldwide, with projections of ecosystem collapse and species extinction in the coming decades (Mellin et al., 2024). Among the responsive drivers of coral reef decline, sediment runoff from tropical deforestation into coastal catchments is a major threat to marine ecosystems including coral reefs (Maina et al., 2013). Deforestation reduces canopy interception of rainfall, evapotranspiration, soil infiltration and moisture retention leading to increased soil erosion (Ellison et al., 2017; Veldkamp et al., 2020). The resulting sediment washes out into rivers and dissipates across marine ecosystems from estuarine pourpoints (Beger et al., 2010; Naciri et al., 2023). High sediment exposure smothers and kills corals and decreases physiological health of coral reef fishes (Hess et al., 2017; Wenger et al., 2014; Wenger et al., 2013; Wenger et al., 2011). Mangrove ecosystems can filter sediments and reduce sediment loads, but they are also facing rapid loss due to anthropogenic activities (Friess et al., 2019). Sediment runoff will likely increase in the coming decades, given projected decreases is forest cover, e.g., in Indonesia (Voigt et al., 2022). However, the spatial patterns of the land use-sedimentation-reef decline nexus and their temporal trends in sediment runoff remain unclear, as does the relative importance of land use change, biological processes, and climate change. This means the risks to coral reefs are poorly quantified and thus many opportunities for reduced deforestation and reforestation to improve forest, mangrove and coral reef health are not realised.

This project will develop and apply new remote sensing techniques to detect and track river and coastal sediment loads. In-situ datasets of sediment load and deposition will be collected and analysed to evaluate remote sensed data. Spatial and temporal patterns in sediment load will be analysed alongside rates of deforestation and location of sensitive marine ecosystems to identify damage hotspots.

The PhD has the following objectives:

1. Use satellite remote sensed data to quantify river sediment loads and their relationship with tropical deforestation and forest degradation.
2. Quantify the flow of sediments within and to marine ecosystems including mangroves, seagrasses and coral reefs and measure how sediment loads impacts marine biota.
3. Use land-use change and climate scenarios to project future changes in sediment load.
4. Detect retention and damage “hotspots” and identify opportunities for forest conservation to have large benefits for marine ecosystems through reduced sediment loads.
5. Communicate results with relevant stakeholders to support joined up land-use management for conservation of tropical forest and marine ecosystems.

A range of remote sensed methods will be explored (e.g., Gardner et al., 2021, 2023) using data from the Sentinel, Landsat and GRACE satellite missions. Existing data on sediment loads (e.g., Grove et al., 2012; Naciri et al., 2023) will be used to evaluate satellite data. Field work will include an assessment of how sediment load affects selected marine biota as well as sediment sampling in the river estuaries to ground truth remote-sensed sediment estimates and create first estimates of how much sediment settles out on contact with sea water. The location of field work will build on existing collaborations of the supervisors and is likely to be at sites in Indonesia.

The project will lead to new understanding of the impacts of tropical deforestation on river sediment loads and marine ecosystem health. Ultimately, we hope the project will provide new knowledge on co-benefits and links between tropical forest and coral reef conservation informing regional conservation priorities.

Skills, Training & Research Groups:

This PhD provides the unique opportunity to work on topics linking tropical forests and coral reefs. It will provide the opportunity to develop and apply skills in satellite remote sensing, data analysis, modelling and quantitative marine ecology. We will support you if you have aspirations to conduct field work. You will be encouraged to develop and strengthen collaborations with conservation and policy stakeholders to ensure evidence from this research has a positive impact on the management of tropical forests and coral reefs. You will be supported to publish your work in leading academic journals and communicate your results as widely as possible.

Candidates for this project should have a background in environmental science, biology, chemistry, physics, mathematics, physical geography, or natural sciences. Crucially, candidates should be keen to learn a wide range of skills from across different disciplines and apply them in new ways to help tackle an urgent conservation challenge.

Supervision across both the School of Earth and Environment and the School of Biology will provide cross-disciplinary support and training. You will join the vibrant Biosphere – Atmosphere Group (BAG) working together with a team of researchers tackling environmental challenges facing the world such  as the impacts of tropical deforestation on local and regional climate. You will become a member of the cross-faculty Leeds Ecosystem, Atmosphere and Forest (LEAF) Centre, which brings together researchers across the university exploring trees, woodlands and forests. In addition, you will collaborate with members of the Marine Transitions Lab, where you can rub shoulders with coral reef scientists, conservation scientists, and think about adaptation.

You will benefit from the training in both specific technical and in transferable skills provided by the YES-DTN and those offered by the University of Leeds.

References

Beger, M., H. Grantham, R. L. Pressey, K. A. Wilson, E. L. Peterson, D. Dorfman, P. J. Mumby, R. Lourival, D. R. Brumbaugh, and H. P. Possingham. 2010. Conservation planning for connectivity across marine, freshwater, and terrestrial realms. Biological Conservation 143:565-575.

Ellison, D., Morris, C. E., Locatelli, B., Sheil, D., Cohen, J., Murdiyarso, D., Gutierrez, V., van Noordwijk, M., Creed, I. F., Pokorny, J., Gaveau, D., Spracklen, D. V., Tobella, A. B., Ilstedt, U., Teuling, A. J., Gebrehiwot, S. G., Sands, D. C., Muys, B., Verbist, B., Springgay, E., Sugandi, Y., and Sullivan, C. A.: Trees, forests and water: Cool insights for a hot world, Global Environ. Change, 43, 51–61, https://doi.org/10.1016/j.gloenvcha.2017.01.002, 2017.

Friess, D. A. et al. The State of the World’s Mangrove Forests: Past, Present, and Future. Annu. Rev. Environ. Resour. 44, 89–115 (2019).

Gardner, J. R., Yang, X., Topp, S. N., Ross, M. R. V., Altenau, E. H., and Pavelsky, T. M.: The Color of Rivers, Geophys. Res. Lett., 48, e2020GL088946, https://doi.org/10.1029/2020gl088946, 2021.

Gardner, J., Pavelsky, T., Topp, S., Yang, X., Ross, M. R. V., and Cohen, S.: Human activities change suspended sediment concentration along rivers, Environ. Res. Lett., 18, 064032, https://doi.org/10.1088/1748-9326/acd8d8, 2023.

Grove, C. A., Zinke, J., Scheufen, T., Maina, J., Epping, E., Boer, W., Randriamanantsoa, B., and Brummer, G.-J. A.: Spatial linkages between coral proxies of terrestrial runoff across a large embayment in Madagascar, Biogeosciences, 9, 3063–3081, https://doi.org/10.5194/bg-9-3063-2012, 2012.

Hess, S., L. J. Prescott, A. S. Hoey, S. A. McMahon, A. S. Wenger, and J. L. Rummer. 2017. Species-specific impacts of suspended sediments on gill structure and function in coral reef fishes. Proceedings of the Royal Society B-Biological Sciences 284.

Maina, J., de Moel, H., Zinke, J. et al. Human deforestation outweighs future climate change impacts of sedimentation on coral reefs. Nat Commun 4, 1986 (2013). https://doi.org/10.1038/ncomms2986

Mellin, C. et al. 2024. Cumulative risk of future bleaching for the world’s coral reefs, Science Advances 10 (26). DOI: 10.1126/sciadv.adn9660

Naciri, W., Boom, A., Payne, M., Browne, N., Evans, N. J., Holdship, P., Rankenburg, K., Nagarajan, R., McDonald, B. J., McIlwain, J., and Zinke, J.: Massive corals record deforestation in Malaysian Borneo through sediments in river discharge, Biogeosciences, 20, 1587–1604, https://doi.org/10.5194/bg-20-1587-2023, 2023.

Veldkamp, E., Schmidt, M., Powers, J. S., and Corre, M. D.: Deforestation and reforestation impacts on soils in the tropics, Nat. Rev. Earth Environ., 1, 590–605, https://doi.org/10.1038/s43017-020-0091-5, 2020.

Voigt, M., H. S. Kühl, M. Ancrenaz, D. Gaveau, E. Meijaard, T. Santika, J. Sherman, S. A. Wich, F. Wolf, M. J. Struebig, H. M. Pereira, and I. M. D. Rosa. 2022. Deforestation projections imply range-wide population decline for critically endangered Bornean orangutan. Perspectives in Ecology and Conservation 20:240-248.

Wenger, A. S., M. I. McCormick, G. G. K. Endo, I. M. McLeod, F. J. Kroon, and G. P. Jones. 2014. Suspended sediment prolongs larval development in a coral reef fish. Journal of Experimental Biology 217:1122-1128.

Wenger, A. S., M. I. McCormick, I. M. McLeod, and G. P. Jones. 2013. Suspended sediment alters predator-prey interactions between two coral reef fishes. Coral Reefs 32:369-374.

Wenger, A. S., J. L. Johansen, and G. P. Jones. 2011. Suspended sediment impairs habitat choice and chemosensory discrimination in two coral reef fishes. Coral Reefs 30:879-887.