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Quantifying seaweed and seagrass beach deposits using high-resolution UAV imagery
Yalei Li1, Hege Gundersen2, Robert Nøddebo Poulsen3
1Section for Marine Biology, Norwegian Institute for Water Research (NIVA), Oslo, Norway; State Key Laboratory of Estuarine and Coastal Research, Institute of Eco-Chongming, East China Normal University, Shanghai, China.
Researchers developed a new method using Unoccupied Aerial Vehicles (UAVs) to accurately quantify beach wrack, which are marine deposits of algae and seagrass. This drone-based approach offers a time- and cost-effective alternative to manual measurements for assessing coastal carbon and nutrient stocks.
Area of Science:
- Coastal Ecology
- Biogeochemistry
- Remote Sensing
Background:
- Beach wrack (macroalgae and seagrass) facilitates ocean-to-land carbon and nutrient transport.
- Beach wrack decomposition influences coastal biochemical cycles.
- Manual quantification of beach wrack is challenging due to terrain and location.
Purpose of the Study:
- To develop and validate a novel method for quantifying beach wrack deposits using Unoccupied Aerial Vehicle (UAV) photogrammetry.
- To assess the accuracy of UAV-based volume and area measurements against traditional methods.
- To quantify carbon and nitrogen content in beach wrack deposits.
Main Methods:
- UAV photogrammetry for spatial mapping and 3D modeling of beach wrack.
- In situ measurements of carbon and nitrogen content in beach wrack samples.
- Validation of UAV volume and cross-sectional area measurements against manual and GNSS data.
Main Results:
- UAV method achieved high accuracy (R² > 0.99) for volume acquisition compared to manual measurements.
- UAV-based cross-sectional area assessments showed high accuracy, with no significant differences from manual and GNSS measurements.
- Quantified beach wrack deposits ranged from 4.3 to 9.7 kg/m (organic carbon) and 0.3 to 0.5 kg/m (nitrogen) in case studies.
Conclusions:
- UAV photogrammetry provides an accurate and efficient tool for quantifying beach wrack, including carbon and nitrogen deposits.
- This method is valuable for ecosystem assessments, blue carbon stock quantification, and environmental monitoring.
- UAVs offer significant time and cost savings over manual methods, especially for large-scale projects.
