Key Takeaways & Executive Findings
- •• • Beach litter density reached 4.41×10^5 items·km−2 (large/very large) and 5.39×10^6 items·km−2 (medium), indicating moderate-to-low pollution compared to global hotspots; plastics comprised 74.0% of beach litter, necessitating targeted plastic waste management. • • Sea surface litter densities (5.82×10^2 and 9.90×10^3 items·km−2 for large/very large and medium) were moderate-to-high, with plastics accounting for 96.0%, highlighting the need for surface cleanup and source reduction. • • Seafloor litter density was 5.20×10^3 items·km−2, relatively low, but 78.8% was plastic, and source analysis linked it to shipping/fishing, indicating the need for port reception facilities and fisher engagement. • • Beach quality assessment showed 63.6% of beaches were moderately clean or better (grades II–IV) and 90.9% were moderately safe or better (grades I–III), providing a baseline for prioritizing management interventions.
Abstract
Marine litter poses a significant threat to coastal ecosystems globally, necessitating a comprehensive understanding of its multi-compartment distribution and driving mechanisms for effective management. This study investigated the occurrence, composition, and sources of beach, sea surface, and seafloor litter in the northeastern Daya Bay, a semi-enclosed bay, during August–October 2024. Sampling included 11 beach transects, 6 surface transects, and 25 seafloor transects. Results showed that the mean density of large and very large beach litter was 4.41×10^5 items·km−2, while medium beach litter reached 5.39×10^6 items·km−2. Surface litter densities were 5.82×10^2 and 9.90×10^3 items·km−2 for large/very large and medium fractions, respectively. Seafloor litter averaged 5.20×10^3 items·km−2. Plastics dominated all compartments, accounting for 74.0% (beach), 96.0% (surface), and 78.8% (seafloor) of total litter. Source apportionment using NOWPAP methodology indicated that beach and surface litter primarily originated from coastal recreational activities, whereas seafloor litter was mainly derived from shipping and fishing. Beach quality assessment revealed that 63.6% of beaches were moderately clean or better (grade II–IV), and 90.9% were moderately safe or better (grade I–III). Hotspots included tourism beaches, tidal gyre areas, coral reef zones, and fishing grounds. The study underscores the need for targeted management, including improved waste collection on tourist beaches, dynamic cleaning protocols, and port reception facilities for fishing waste.
1. Introduction
Marine litter contamination has escalated into a global environmental crisis, with semi-enclosed bays particularly vulnerable due to limited water exchange and intense anthropogenic pressures. Existing monitoring programs often rely on sparse sampling and single-compartment assessments, failing to capture the dynamic transfer of litter across beach, sea surface, and seafloor. This fragmented approach impedes the development of holistic mitigation strategies, as sources and sinks remain poorly constrained. In Daya Bay, a semi-enclosed bay within the Guangdong-Hong Kong-Macao Greater Bay Area, previous surveys by the Ministry of Ecology and Environment provided only partial data on beach and surface litter, leaving seafloor litter largely uncharacterized.
This study addresses these gaps by conducting a simultaneous, multi-compartment survey of beach, sea surface, and seafloor litter in the northeastern Daya Bay. By employing standardized sampling protocols and source apportionment, we quantify litter densities, composition, and spatial distribution, and evaluate beach quality using the Beach Quality Index. The findings provide critical empirical data to inform targeted pollution control and management in semi-enclosed coastal ecosystems, bridging the knowledge gap between litter sources and sinks.
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LIU Bingjie, LU Yao, YE Kuangmin, LI Guodong, DENG Hanqiang, SUN Kaifeng, JU ... (2026). Occurrence Characteristics, Source Analysis, and Beach Quality Assessment of Marine Litter in Daya Bay. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202509067
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Frequently Asked Questions
What are the dominant litter types and their proportions in each compartment, and how do they inform source-specific management?
Plastics dominated all compartments: 74.0% on beaches, 96.0% on the sea surface, and 78.8% on the seafloor. Common items included cigarette butts, plastic fragments, bags, bottles, ropes, and fishing nets. The high plastic proportion, especially on the sea surface, indicates that reducing single-use plastics and improving waste management on land and at sea are critical. The presence of fishing-related items on the seafloor suggests targeted measures for the fishing industry.
How do the litter densities in Daya Bay compare with other semi-enclosed seas, and what does this imply for regional pollution status?
Beach litter densities (4.41×10^5 to 5.39×10^6 items·km−2) were moderate-to-low compared to the Mediterranean (1.06×10^6 items·km−2) and Turkey (1.95×10^7 items·km−2). Sea surface densities (5.82×10^2 to 9.90×10^3 items·km−2) were moderate-to-high, while seafloor density (5.20×10^3 items·km−2) was lower than the Mediterranean (7.90×10^5 items·km−2). This suggests that while Daya Bay is not as polluted as some enclosed seas, the high plastic fraction and localized hotspots warrant immediate action.
What are the primary sources of marine litter in each compartment, and how were they determined?
Using the NOWPAP source apportionment method, beach and sea surface litter were primarily attributed to human coastal activities (e.g., tourism, recreational beach use), indicating land-based inputs. In contrast, seafloor litter was mainly sourced from shipping and fishing activities, representing marine-based inputs. This distinction is crucial for designing targeted interventions: improving coastal waste management for beach/surface litter, and implementing port reception facilities and fisher engagement for seafloor litter.
Which specific areas within the study region are identified as hotspots, and what management actions are recommended?
Hotspots include tourism beaches (e.g., Weihai Bay, Blue Bay Beach), tidal gyre areas in the northeast, coral reef zones around Pingshi Island, and fishing-intensive areas like Fanhe Harbor. For tourism beaches, recommendations include installing separate collection bins for cigarette butts and plastic bottles, and posting environmental reminders. For gyre and coral areas, regular cleanups and monitoring are advised. For fishing areas, establishing port reception facilities and incentivizing fishers to return waste to shore are key.
How was beach quality assessed, and what do the grades indicate for management prioritization?
Beach quality was evaluated using the Beach Quality Index (BQI), which incorporates litter abundance, composition, and safety. Results showed that 63.6% of beaches were moderately clean or better (grades II–IV), and 90.9% were moderately safe or better (grades I–III). This indicates that while overall cleanliness is moderate, safety is relatively high. Beaches with lower grades should be prioritized for cleanup and infrastructure improvements.
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