Dana Lanceman, PhD Candidate, UNSW / Associate Professor William Glamore, Water Research Laboratory, UNSW / Doctor Mahmood Sadat-Noori, Water Research Laboratory, UNSW

In an era of simultaneous biodiversity and climate crises, ecosystem restoration is rapidly emerging as an effective approach to help tackle both challenges. In particular, restoration of marine vegetation communities, or blue carbon ecosystems, is extremely important, as these ecosystems can sequester and store more carbon than their terrestrial counterparts, while also supporting a great diversity of aquatic and terrestrial organisms.

However, restoring coastal wetlands is challenging for several reasons. One of these reasons is that wetlands are often difficult to access and costly to monitor. Remote sensing monitoring, including the use of satellites, aerial imagery, drones, LiDAR and radar, has been increasingly used alongside or instead of ground-based methods to survey wetlands and other ecosystems. These images can then be classified to map vegetation communities and calculate changes over time.

Drones for versatile, high-resolution image capture

Drones are an excellent platform for capturing wetland imagery as they can be deployed at the spatial scale and time of choice, and can capture many different types of data at an extremely high-resolution (up to <1 cm). User flexibility in deciding when and where drones are flown allows the entire wetland of interest to be captured at favourable time periods, compared to satellite imagery which may be affected by cloud cover or capture images at unsuitable tides. Users can also choose which type of drone they deploy, capturing the most relevant types of data for their projects. Drones can even be used to capture elevation data, through photogrammetry, where multiple overlapping images are used to calculate the elevation of landscape elements. High resolution drone data allows detection and accurate quantification of the area and distribution of each habitat type within complex habitat mosaics (e.g. mangroves, saltmarsh, seagrass and mudflat), which is important for estimating blue carbon storage volumes from different types of wetland vegetation.

Dr Mahmood Sadat-Noori with drones used to monitor the restoration progress of a blue carbon restoration site at Kooragang Island.

Case study: Kooragang wetlands, Hunter estuary, NSW

Our research team at UNSW Water Research Laboratory has been involved in coastal wetland restoration and drone monitoring for many years. We decided to use drones to track wetland vegetation change and estimate carbon abatement over time at a 20 ha tidally restored saltmarsh site at Koorangang Island. We captured high resolution multispectral and photogrammetric elevation drone data at regular intervals over four years, and developed an open-source method for image classification and analysis. Using these methods, we were able to classify the three dominant species of saltmarsh on site to the species level, explore patterns of growth of each species and estimate carbon abatement (using the BlueCAM method) over the restoration period.

Trajectory of saltmarsh growth at a blue carbon restoration site over four years. Images classified from drone imagery. Figure developed by Dana Lanceman.

Learnings about the evolution of blue carbon sites

Many wetland restoration projects measure wetland vegetation at a single time point before and after restoration, or classify vegetation at a coarser level (e.g. “wetland vegetation”, or “saltmarsh” rather than classifying to a species level). By capturing and classifying high resolution drone images at seven time points during our restoration site’s evolution, we were able to gain insights about finer scale trends in saltmarsh growth and interactions between species.

We found that although saltmarsh wetlands in this region are usually jointly dominated by two species (Sporobolus virginicus and Sarcocornia quinqueflora), saltmarsh growth at our restoration site was strongly dominated by one species (Sarcocornia quinqueflora). We hypothesise that one factor driving this imbalance is the difference in reproductive strategies between the two species (see discussion in Rankin et al. 2022). Sarcocornia reproduces by seeds, meaning it could quickly spread and grow from many locations throughout the wetland at once, whereas Sporobolus mainly reproduces by rhizomes, or underground stems connected to existing plants, restricting where it was able to spread. These reproductive strategies were apparent when we explored the spatial patterns of growth of each species – Sarcocornia made thousands of clumps and spread from there, whereas Sporobolus mainly expanded from existing vegetation. Why does the imbalance in species matter? In terms of carbon sequestration, it may not make a difference if both species had similar sequestration and storage capacities (this would have to be investigated), but faunal biodiversity is going to be limited with a less diverse vegetation community. This highlights the need to consider the ecological traits of species in restoration projects.

Restored saltmarsh at Kooragang wetlands in 2022 – the site was bare mud in 2017.

Challenges and where to next

The field of blue carbon restoration and monitoring is constantly evolving. Although drones have many advantages as outlined here, they cannot easily capture large areas and can be costly to deploy. Very high-resolution satellite imagery might be the way of the future – if this sort of imagery becomes more accessible. Certainly, there is still much to learn about cost-effective remote sensing techniques, trajectories of wetland evolution and optimising blue carbon capture – but we think this sort of research is a great place to start!

Project lead Associate Professor William Glamore with some of the wetland restoration team at Kooragang Island restoration site.

If you are keen to know more about this site, the tidal restoration technique used (Tidal Replicate Method), its ecological restoration results and other fieldwork and findings at the site, refer to the below published papers:

Rankin, C., Gaston, T., Sadat-Noori, M., Chalmers, A., Glamore, W., Morton, J., (2022). Innovative tidal control successfully promotes saltmarsh restoration. Ecological Restoration. https://doi.org/10.1111/rec.13774.

Sadat-Noori, M., Rankin, C., Rayner, D., Heimhuber, V., Drummond, C., Khojasteh, D., Gaston T., and Glamore, W. (2021). Coastal wetlands can be saved from sea level rise by recreating past tidal regimes. Scientific Reports, 11: 1196. https://doi.org/10.1038/s41598-021-80977-3 .