Leakage of plastics and other debris from landfills to a highly protected lake by wintering gulls

The study, led by the Institut de Ciències del Mar and Estación Biológica de Doñana, CSIC, Spain, used diet samples collected in January 2022 at the Fuente de Piedra – an inland lake in Spain that is internationally important for biodiversity. Monthly counts of Lesser Black-backed Gulls were carried out to assess the numbers of birds present at the lake. GPS tracking data collected from studies across Northern Europe, including some led by BTO, were used over 12 ‘winters’, between January to March 2010–22, to understand the spatial movements of individual birds in the local region, coinciding with when birds are either on wintering grounds or on migration.

The authors found that a high proportion (94%) of material regurgitated by gulls contained human-related material such as glass and textiles and 86% contained plastics, whereas only 1% plastic mass was present in faeces. Numbers of Lesser Black-backed Gulls at the lake were highest in January, peaking at a maximum count of 33,000 in January 2020. Agricultural habitats were most frequently used by gulls (88% time) as well as three landfill sites in the local area, with some landfills visited more than others, linked to use of bird deterrence measures. A total of 77% of the tracked birds visited at least one of the three landfills on a given day. The authors estimated that, on average, the annual deposition of plastic and other debris by the wintering gull population into the lake was 1,888 g per day, meaning that 400 kg of plastic were estimated to be deposited into the lake each winter, though only ca. 5 kg were from faeces.

This study sheds new light on the importance of gulls for biovectoring within ecosystems, and the leakage of plastic and debris from landfills into inland waters. The plastics can accumulate in sediments and become incorporated into food webs, presenting a global contamination issue that needs addressing. The study further highlights the importance of adopting initiatives to tackle the problem, such as waste separation and plastic reduction measures, and bird-deterrence to reduce ingestion by birds at source. 

Notes

For UK sites, this work was funded by the Department for Energy Security and Net Zero (DESNZ), through the Offshore Energy Strategic Environmental Assessment research programme, with the contract managed by John Hartley (Hartley Anderson Ltd), and was further funded by Ørsted, and supported by the Marine Renewable Energy and the Environment (MaREE) project (funded by Highlands and Islands Enterprise, the European Regional Development Fund and the Scottish Funding Council).