Day 4

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Paper title Beach and shallow sea wrack spatial distribution detection using unmanned areal vehicles
Authors
  1. Edvinas Tiškus KU Marine Research Institute Speaker
  2. Diana Vaičiūtė KU Marine Research Institute
  3. Martynas Bučas Klaipeda University Marine Research Institute
  4. Jonas Gintauskas Klaipeda University Marine Research Institute
  5. Viktorija Sabaliauskaitė KU Marine Research Institute
Form of presentation Poster
Topics
  • C4. HAPs/UAVs
    • C4.01 Innovative UAV applications
Abstract text Beach wrack is a term used to describe organic matter, e.g., aquatic plants, macroalgae, that is washed from the sea to shore due to wind, waves or floods. These organic matter accumulations are home to invertebrates, which in turn are food for animals in the higher food chain, such as seabirds. Algal accumulations also perform important coastal protection – dune stabilization by reducing the impact of wave energy and wind-induced sand transport processes.
From a socio-economic point of view, beach wrack accumulations are often considered an inconvenience, especially for tourists when large amounts are discarded on resort beaches. After storms, they can cover large areas of beach, begin to decompose, and emit unpleasant odors. In order to ensure proper conditions for tourists and have clean beaches, municipalities managing the beaches should clean them from decomposing organic matter, taking into account the accumulated organic deposits.
Beach wracks are essentially unpredictable and heterogeneous material, whereof different parts may be at different stages of decomposition. Because algae are often mixed with debris and large amounts of sand, they are expensive to manage and processing options are often difficult. Studies have shown that various plastic fractions are trapped in algae and thus the plastic is removed from the sea to shore.
In order to map and more accurately estimate the areas of algal deposits in time and space, it is recommended to use an unmanned aerial vehicle (drone), which can provide spatial information useful for studying small changes in space and time. Beach wrack mapping by drone has been successfully tested in Greece, but its accuracy and wrack content have not been evaluated (Papakonstantinou et al., 2016).
The main aim of this study is to estimate the amount of algal deposits and the plastic in it. This study is expected to:
1) Assess the area of wrack deposits in the four studied Lithuanian Baltic Sea beaches;
2) Apply the volume calculation method using the obtained virtual height models and subtracting different topographic surfaces from them, which will be validated with the algae heights measured with a ruler;
3) Estimate the probable amounts of plastic in the assemblies.
The research was carried out on four beaches: Melnragė, Karklė, Palanga and Šventoji. A DJI Inspire 2 drone with a Zenmuse X5S camera was used for the flights. The flights are performed at an altitude of 60 m, which allows to get high-resolution (up to 2 cm/pixel) photos. A RedEdge MX multispectral camera was used for an additional detection experiment.
The first flights and mapping were performed in 2020 August. From 2021 April 20 continuous monitoring started, which continued throughout the summer season. Monitoring was performed every 10 days (depending on weather conditions). Beaches were mapped only when wrack deposits were observed.
Expeditions are carried out at least once a month or when a big wrack is detected, during which the heights of wrack deposits are measured in situ and the coordinates of the measurements are recorded. This data were used to validate the height models obtained from the drone at the points. Expeditions also include sampling to determine the biomass and species diversity of macroalgae assemblages, and the amount of plastic items.
The photographs taken by the drone are combined into orthophotos and then transferred to a GIS program, in which automatic classification divides pixels into groups: water, sand and algal deposits. After machine learning step each area size is calculated. Volume is calculated from virtual elevation models.
Based on the biomass of macroalgae determined in the laboratory, the results are extrapolated and their volume is calculated for the whole area. Extrapolation is also performed with plastic, which is checked in different fractions: < 0.5 cm – micro, 0.5–2.5 cm – meso and > 2.5 – macro.
Observations showed the highest algal exudation was in Melnragė and Šventoji beaches (18 times out of 20 (90%) and 10 out of 14 (71%), respectively). Accumulations were detected 8 times out of 17 (47%) in Karklė and 4 out of 13 (31%) in Palanga.
This data and methodology could be used for the management of beach areas by detecting, calculating the amount of macroalgal biomass and associated plastic amount prior the decision making.