Dongshan Bay Research Articles

Tidal variability and microplastics distribution: source analysis in Dongshan Bay beach sediments, South China

Tidal variability and microplastics distribution: source analysis in Dongshan Bay beach sediments, South China

Impact of Nutrient Enrichment on Community Structure and Co-Occurrence Networks of Coral Symbiotic Microbiota in Duncanopsammia peltata: Zooxanthellae, Bacteria, and Archaea.

Symbiotic microorganisms in reef-building corals, including algae, bacteria, archaea, fungi, and viruses, play critical roles in the adaptation of coral hosts to adverse environmental conditions. However, their adaptation and functional relationships in nutrient-rich environments have yet to be fully explored. This study investigated Duncanopsammia peltata and the surrounding seawater and sediments from protected and non-protected areas in the summer and winter in Dongshan Bay. High-throughput sequencing was used to characterize community changes, co-occurrence patterns, and factors influencing symbiotic coral microorganisms (zooxanthellae, bacteria, and archaea) in different environments. The results showed that nutrient enrichment in the protected and non-protected areas was the greatest in December, followed by the non-protected area in August. In contrast, the August protected area had the lowest nutrient enrichment. Significant differences were found in the composition of the bacterial and archaeal communities in seawater and sediments from different regions. Among the coral symbiotic microorganisms, the main dominant species of zooxanthellae is the C1 subspecies (42.22-56.35%). The dominant phyla of bacteria were Proteobacteria, Cyanobacteria, Firmicutes, and Bacteroidota. Only in the August protected area did a large number (41.98%) of SAR324_cladeMarine_group_B exist. The August protected and non-protected areas and December protected and non-protected areas contained beneficial bacteria as biomarkers. They were Nisaea, Spiroplasma, Endozoicomonas, and Bacillus. No pathogenic bacteria appeared in the protected area in August. The dominant phylum in Archaea was Crenarchaeota. These symbiotic coral microorganisms' relative abundances and compositions vary with environmental changes. The enrichment of dissolved inorganic nitrogen in environmental media is a key factor affecting the composition of coral microbial communities. Co-occurrence analysis showed that nutrient enrichment under anthropogenic disturbances enhanced the interactions between coral symbiotic microorganisms. These findings improve our understanding of the adaptations of coral holobionts to various nutritional environments.

Marine Ecological Damage Assessment Model for Offshore Oil Extraction

<p>With the progress of society and the development of the economy, people’s awareness of environmental protection is also becoming stronger. Therefore, the damage caused by marine oil spills caused by offshore oil extraction to marine ecology is also receiving more and more attention from people. Marine ecological damage assessment involves various disciplines such as environmental chemistry, biology, toxicology, and hydrodynamics, and requires a large amount of data support, making it a challenge in the field of marine claims. To quantitatively evaluate marine oil spill accidents, the Spill Impact Model Application Package model is used as the system framework to build a marine ecological damage assessment model. The MIKE21 model is used for physical fate simulation, while the biological effects model is used for resource damage assessment of the ecological environment and aquatic organisms. The model is validated using the oil spill accident in Dongshan Bay as an example. The validation results show that the total loss of aquatic organisms under conditions 1 and 2 is 67.30 tons and 56.03 tons, respectively. Under condition 1, the ecological environment of coral and mangroves is affected by an area of 8.805km2 and 5.859km2, respectively, resulting in a loss of 19.5168 million yuan in ecological resources. Under condition 2, the ecological environment of coral and mangroves is affected by an area of 7.646 km2 and 13.515 km2, respectively, resulting in a loss of 26.322 million yuan in ecological resources. In summary, it can be seen that the research on marine ecological damage assessment models for offshore oil extraction provides certain reference value for the field of marine ecological damage assessment in China.</p>

Evaluation of excess Th-228 in surface bottom sediment of shallow marine ecosystem: a case study from Dongshan Bay

Evaluation of excess Th-228 in surface bottom sediment of shallow marine ecosystem: a case study from Dongshan Bay

On-site monitoring of dissolved Sb species in natural waters by an automatic system using flow injection coupled with hydride generation atomic fluorescence spectrometer

Antimony (Sb) is a toxic and potentially carcinogenic element in the environment. The toxicity of Sb(III) is ten times that of Sb(V). Therefore, on-site monitoring technique for dissolved Sb species is crucial for the study of Sb environmental processes. In this study, an automated, portable, and cost-effective system was developed for field simultaneous analysis of Sb(III) and Sb(III + V) in natural waters. The system comprised a portable atomic fluorescence spectrometer equipped with a built-in electrochemical H2 generator to reduce the consumption of acid/borohydride solution and make the atomizer more stable for on-site analysis. Flow injection technique was also used to achieve on-line pretreatment of water samples, including filtration, acidification, pre-reduction, and hydride generation procedures. Under the optimal conditions, the limits of detection (3σ, n = 11) of the developed method were 0.015 μg/L and the linear ranges were 0.05–5.0 μg/L for both Sb(III) and Sb(III + V). The relative standard deviations (n = 11) of the spiked samples of Sb(V) were 3.2% (0.05 μg/L), 3.3% (0.2 μg/L), and 1.7% (0.5 μg/L), respectively. The spiked recoveries of lake water, treated wastewater, and seawater ranged from 97.0% to 108.5%. The novel system of flow injection coupled with hydride generation atomic fluorescence spectrometer (FI-HG-AFS) was applied to carry out an 18-h fixed-point monitoring at a secondary settling tank of a wastewater treatment facility in Xiamen University, and a 6-h real-time underway analysis in the surface seawater of Dongshan Bay, China, proving that the system was capable of long-term monitoring in the field.

Heavy Metals in the Sediments of Dongshan Bay, China: Sources, Distribution, and Controlling Factors

Fifty-one surface sediment samples from Dongshan Bay, China, were analyzed for heavy metals to evaluate their distribution, pollution status, and controlling factors. The enrichment factor is suggestive of the potential pollution status, ranging from minimal to moderate enrichment, for Pb, As, Zn, and Hg, with one site showing significant enrichment in As. A principal component analysis and the geochemical characteristics indicate that heavy metal concentrations are mainly influenced by clay minerals and Fe oxides, while Pb and Hg levels are also closely linked to the absorption of Mn oxides. Potential pollution is primarily from aquaculture (Cd, Zn, Cu, Pb) and industrial and domestic discharges. Approximately 270 tons of heavy metals were estimated to have been deposited in Dongshan Bay in 2021, highlighting the potential impact of human activities on coastal sediment quality.

Critical factors driving spatiotemporal variability in the phytoplankton community structure of the coral habitat in Dongshan Bay, China.

This study investigated the spatiotemporal distribution of the phytoplankton in the coral habitat of Dongshan Bay (China), along with critical factors affecting the distribution, during June, August, and December 2022. Phytoplankton abundance in Dongshan Bay exhibited considerably temporal variation, peaking in June 2022, gradually decreasing thereafter, and reaching its lowest point in December 2022. The abundance of bottom-layer phytoplankton consistently exceeded that of the surface layer throughout all seasons. The average phytoplankton abundance in the coral habitat of Dongshan Bay was lower than that in non-coral habitat areas. Fluctuations in the Zhangjiang River and coastal upwelling influenced the diversity and community structure of the phytoplankton. Critical factors causing spatiotemporal variability in phytoplankton community structure included nutrient concentrations and seawater temperature. Nutrients played key roles in influencing various phytoplankton groups. Dominant diatom species, such as Thalassionema nitzschioides and Thalassiosira diporocyclus, were positively correlated with ammonia nitrogen, seawater salinity, coral cover, and the number of coral species present. In winter, Calanus sinicus exhibited a negative correlation with harmful algal bloom species. Additionally, it was found that both in the coral habitat and surrounding open sea, currents, nutrients, and zooplankton may play crucial roles in determining the spatiotemporal variability in the phytoplankton community structure.

The first record of Egglestonichthys bombylios (Gobiiformes: Gobiidae) from China with its first fresh colouration information.

During bottom trawl surveys carried out between 20132021, 52 specimens (33.854.0 mm SL) of Egglestones bumblebee goby Egglestonichthys bombylios were collected at a depth of 1.515 m from Dongshan Bay, Sanmen Bay, and Niushan Island, China. They represent the first records of this species from China. A full description, including fresh colouration of the species is provided as it is poorly known. The individuals collected in China agree with most morphological features of the holotype, except for the pelvic fin fraenum that was not observed or appears to be absent in most specimens. A strong relationship between E. bombylios, Larsonella pumilus, and the genus Priolepis is herein demonstrated by the mitochondrial genome sequences of E. bombylios and twenty closely related species. This study enriches the existing genetic data of the so-called Priolepis lineage and provides useful insights into the phylogenetic relationships across species of the genera Egglestonichthys, Priolepis, and Larsonella.

Characterizing 226Ra and its daughters in coastal zone groundwater of a typical human-activity affected bay: occurrence, safety, and source evaluation.

Due to their extremely toxic properties, 226Ra and it daughters (222Rn, 210Pb, and 210Po) in drinking groundwater require monitoring. Recent studies have reported exceptionally high levels of natural 210Po (up to 10,000Bq/m3), 226Ra, and 222Rn isotopes in groundwater. This study aims to provide background data on 226Ra and its daughter radionuclides in the typical agricultural-industrial Dongshan Bay (DSB) before the construction of Zhangzhou Nuclear Power Plant (Zhangzhou NPP). The measurement results indicate that no abnormally high activities of 210Po and 210Pb were detected in the investigated wells. Strong positive correlations between 210Pb and 210Po, as well as between 222Rn and 210Pb activities, suggest that the origins of 210Pb and 210Po in groundwater are strongly influenced by the decay of the parent radionuclides 222Rn and 210Pb, respectively. In the DSB coastal zone groundwater, significant deficiencies of 210Po relative to 210Pb and 210Pb relative to 222Rn were observed, providing further evidence that 210Po and 210Pb are also effectively scavenged due to their geochemical properties (specifically particle affinity) within the groundwater-aquifer system. A systematic comparison among all relevant water bodies in the DSB revealed that the activity concentrations of 210Pb and 210Po in groundwater were the highest, except for rainwater. Based on the evaluation of 210Pb sources, the results imply that submarine groundwater discharge (SGD) is an important pathway for transferring radionuclides (such as 210Pb) from land to the nearshore marine environment, even though the study area has a lower 210Pb background groundwater. By considering all the 210Pb's sources in the DSB, we found low 210Pb background groundwater discharge still needs to be taken into account for small-scale bays. This is because SGD was calculated to be one of the most important 210Pb sources in the bay during observation season. Regardless of whether the system is in a normal state or a nuclear accident emergency state, greater attention should be paid to the groundwater discharge of radionuclides into the ocean.

Per- and polyfluoroalkyl substances in a subtropical river-mangrove estuary-bay system

Mangrove estuaries are one of the most economically valuable and biologically diverse coastal ecosystems. However, knowledge of emerging pollutants in mangrove estuaries is limited. This study provided insight into the PFAS in a river (Zhangjiang River, ZR)-mangrove estuary (Zhangjiang River Estuary, ZRE)-bay (Dongshan Bay, DSB) continuous system in Fujian Province, China. The Σ25PFAS (sum of 25 PFAS) concentrations (0.94 ∼ 62.44 ng/L) showed a declining trend from the river to bay. The Zhe-Min Coastal Current (ZMCC) can transport an abundance of PFAS, especially PFOA, from the northern sea to southern bays, which can affect the seasonal distribution of PFAS concentrations in the DSB and result in PFOA/Σ25PFAS with a decreasing trend in the DSB (28.08%), ZRE (21.15%), and ZR (14.13%), respectively. The primary PFAS sources in this area determined by the positive matrix factor model mainly contained the effluent of the wastewater treatment plant neighboring the R2 site, discharge of domestic and production wastewater, irregular emissions of aqueous film-forming foams, and fluorochemistry industry wastewater transmitted from the ZMCC. The PFAS pollution in the mangrove creek was mainly affected by the discharge of domestic and production wastewater and presented a significant point source pollution, especially during the rainy season.

Integrated assessment of trace elements contamination in sediments of a typical aquaculture bay in China: Ecological toxicity, sources and spatiotemporal variation

Trace elements contamination in estuarine and bay ecosystems has become a serious problem, especially in bays with frequent aquaculture activities. To explore the pollution risk, sources and trends of pollution trace elements in Dongshan Bay, a typical aquaculture bay in China, the concentration and spatial distribution of seven trace elements in surface sediments were investigated. In this study, Zn was the element with the highest content in surface sediments, followed by Pb and Cr, while Cd was the lowest, but the average concentrations of Cd and Hg exceeded the regional background values. High levels of trace elements were distributed in estuaries and aquaculture areas, which were illustrated also by the SOM model. An evaluation of the pollution load index (PLI), geo-accumulation index (Igeo) and potential ecological risk index (PERI) demonstrated that Cd and Hg were the principal pollution elements and ecological risk factors in the surface sediments of the Bay. A positive matrix factorization model (PMF) revealed that the main sources of trace elements were natural sources, petrochemical industry and fossil fuel combination emissions, use of agricultural fertilizer, and industrial and agricultural sewage discharge. Comparative analysis found that since 2008, the mean content of Cu, Pb, Zn, and As have decreased significantly, while the content of Cd, Hg, and Cr have increased significantly. This information will help marine management efforts in taking effective measures to prevent environmental risks caused by trace elements pollution, especially related to aquaculture.

Changes of eutrophication degree in Dongshan Bay in China affected by the COVID-19 outbreak

At the background of the outbreak of COVID-19 pandemic, water samples were collected in Dongshan Bay from 2019 to 2020, to study spatial and temporal changes of nutrients concentration and eutrophication degree with a new assessment model–PE3. Results showed that the spatial distribution of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and dissolved silica (DSi) generally decreased from Zhangjiang River estuary to the mouth of the bay and from west to east both in spring and summer. This pandemic seems to have little influence on the spatial distribution of DIP and DSi. However, DIN concentration decreased much greatly from 2019 to 2020, meanwhile N replaced P to be the potentially limited nutrient factor for the growth of phytoplankton. And average eutrophication degree of the bay assessed by PE3 increased from 1 in 1988 to 5 in 2008 and 6 in 2019 respectively, and decreased to 4 in 2020. It was suggested that after this pandemic, DIN concentration and eutrophication degree may decrease a lot in Chinese coastal waters.

Vertical distribution and pollution assessment of TN, TP, and TOC in the sediment cores of cage farming areas in Dongshan Bay of southeast China

Cage farming is an important means of aquacultural production, while its potential environmental pollution needs to be further investigated. In this study, Dongshan Bay was taken as an example to investigate whether long-term cage farming in a semi-closed bay would cause environmental pollution via vertical distribution assessment. The four sediment cores (YB1, YB2, B1, and B2) were collected from two cage farming areas. Total nitrogen (TN), total organic carbon (TOC), and total phosphorus (TP) were measured. The results showed a negative correlation between TN and TOC and the sediment depth at four sampling sites, and TP was also negatively correlated with the depth at three sites. The average TN (1,405.8, 1,413.8, 1,115.7, and 936.1 mgkg−1) and TP (1,206, 1,141.6, 1,064.6, and 932.8 mgkg−1) values of the four sites were markedly higher than the safety level, with the indexes STN, STP, FF, and ON of the four sites indicating moderate to severe pollution of nitrogen and phosphorus. Particularly, the YB1 and YB2 sites in the area with lower current speed have more severe pollution. The C/N ratio uncovered that the organic matter (OM) might mainly derived from the phytoplankton and nonfibrous plants as a result of excessive fish feed and feces. Collectively, the results indicated that long-term (more than 10 years) cage farming activity in a semi-closed bay such as Dongshan Bay had a negative impact on the environmental quality. Despite limitations in sample size and the absence of stable isotopic analyses, this study enhances our understanding of environmental changes and endogenous pollution risks in shallow marine aquaculture areas. Moreover, it suggests practical approaches such as implementing alternative farming and fallowing periods, should be conducted to mitigate the pollution.

Performance, community dynamics and network of an aerobic denitrifying consortium from a coastal mariculture area

Use of aerobic denitrifying consortia, as a new efficient tool for nitrogen removal, has attracted widespread attention because of their stable and efficient nitrogen removal ability. Yet, little attention has been given to highly efficient aerobic denitrifying consortia from mariculture environments. In this study, a natural aerobic denitrifying consortium, named C3, was obtained by an enrichment technique from a coastal mariculture area of Dongshan Bay of Fujian Province, China. In culture, it exhibited good and stable nitrate removing performance. Nitrogen mass balance indicated that 49.30% of the initial TN was converted into gaseous nitrogen and 49.63% was assimilated to biomass nitrogen. High-throughput sequencing and network analysis revealed that Pseudomonas and Fusarium were putative dominant aerobic denitrifying bacterial and fungal species, respectively, cooperating with Exophiala, Penicillium, Mortierella, Neocamarosporium, Neocosmospora, Sterigmatomyces, Thelebolus, Thermomyces, Cutaneotrichosporon and Gymnopilus to perform aerobic denitrification. In addition, four Pseudomonas strains have been successfully isolated from consortium C3, which supported the inference that Pseudomonas was the dominant contributor in the aerobic denitrifying consortium C3. These results will offer novel insights into aerobic denitrifying consortia in mariculture environments for biotechnological nitrogen pollution removal.

Submarine groundwater discharge in Dongshan Bay, China: A master regulator of nutrients in spring and potential national significance of small bays

Despite over 90% of China’s coastal bays have an area less than 500 km2, the geochemical effects of SGD on those ecosystems are ambiguous. Based on mapping and time-series observations of Ra isotopes and nutrients, a case study of small bays (<500 km2), we revealed that submarine groundwater discharge (SGD) predominately regulated the distribution of nutrients and fueled algal growth in Dongshan Bay, China. On the bay-wide scale, the SGD rate was estimated to be 0.048 ± 0.022 m day−1 and contributed over 95% of the nutrients. At the time-series site where the bay-wide highest Ra activities in the bottom water marked an SGD hotspot with an average rate an order of magnitude greater, the maximum chlorophyll concentration co-occurred, suggesting that SGD may support the algal bloom. The ever-most significant positive correlations between 228Ra and nutrients throughout the water column (P< 0.01, R2 > 0.90 except for soluble reactive phosphorus in the surface) suggested the predominance of SGD in controlling nutrient distribution in the bay. Extrapolated to a national scale, the SGD-carried dissolved inorganic nitrogen flux in small bays was twice as much as those in large bays (>2,000 km2). Thus, the SGD-carried nutrients in small bays merit immediate attention in environmental monitoring and management.

Reinforced human intervention drives microplastic pollution in estuarine beaches and nearshore sediments of Dongshan Bay, China

Sediments are generally recognized as a critical source and sink of microplastics (MPs), yet sedimentary MPs in the coastal areas are relatively overlooked. This study investigated MP pollution in estuarine beaches and nearshore sediments in Dongshan Bay in Southeastern China. The 23 sampling sites encompass the mangrove zone, west coast, south coast, east coast, and shipping-lane zone. MPs were evaluated by abundance, size, shape, color, composition, and morphology using microscopic identification, micro-Raman spectroscopy, and scanning electron microscopy. The abundance of MPs in surface sediments across Dongshan Bay manifested spatial heterogeneity, ranging from 31 to 971 items per kg d.w. The prominent concentration of MPs in the mid-west coast seemed to be driven by reinforced human intervention, namely, a giant facility under construction in the vicinity of the west coast. The major shape, color, and type of MPs were fiber, white and black, PES, PET, and PS, respectively. Friction, abrasions, scratches, and depressions were often present at the surfaces of MPs. The distribution patterns and hotspots of sedimentary MPs mirrored profound human footprints. This study provided insights into the assessment of estuarine ecosystem vulnerability and mitigation strategies against pressing sedimentary MP issues.

Distinct response of total and active fungal communities and functions to seasonal changes in a semi‐enclosed bay with mariculture (Dongshan Bay, Southern China)

AbstractIncreasing evidence suggests that fungal communities are key components of biogeochemical cycles in coastal ecosystems. However, at a regional scale, the major drivers of the seasonal and spatial distribution of fungi in areas impacted by mariculture remain largely unknown. Intensive aquaculture takes place in Dongshan Bay of Fujian, China, a typical subtropical marine ecosystem with multiple environmental gradients extensively perturbed by anthropogenic activities. To better understand the consequences of mariculture on fungal community composition and activities, we simultaneously evaluated the temporal (four different seasons) and spatial dynamics in total (DNA) and active (RNA) fungal communities of Dongshan Bay in relation to several major physicochemical properties. Our results revealed that fungal communities in the Bay were highly diverse, but showed the ubiquitous dominance of Dikarya and the occasional predominance of Glomeromycota, Mucoromycota, Mortierellomycota, Chytridiomycota, Olpidiomycota, and Rozellomycota. Fungal diversity varied much more with season than with the degree of aquaculture activity, for both total and active communities. This notion is supported by co‐occurrence networks exhibiting a clear seasonal pattern. Furthermore, fungal community structure in coastal waters showed distinct relationships with environmental factors varying both with season and in space. For both total and active fungal communities, a combination of environmental variables including temperature, dissolved oxygen, and nitrite exhibited the greatest impact on community structure. Our study demonstrates a distinct spatiotemporal dynamics of both total and active fungi and provides a foundation to better understand the ecological roles of marine fungi in coastal ecosystems in relation to mariculture activities.

A novel framework-based meta-analysis for in-depth characterization of microplastic pollution and associated ecological risks in Chinese Bays.

Among aquatic ecosystems, bays are ubiquitously contaminated with microplastics (MPs, size <5mm), but a comprehensive understanding of their pollution characterization in Chinese Bays is largely elusive. The current study aims to systematically highlight factors intricating MP contamination as well as their geographic distribution, interactions, risk evaluation, and abundance prediction in bays. MPs' abundance was varied in different bays, at concentrations ranging between 0.26±0.14-89, 500±20, 600 items/m3 in water, 15±6-6433.5 items/kg dry weight in sediment and 0.21±0.10-103.5 items/individual in biota. Redundancy analysis, Permannova, and GeoDetector model revealed that the sampling and extraction/identification methods, and geographical locations were the major drivers affecting MP distribution and characteristics. The Mantel test highlighted that the MP characteristics changed with geographic distance, higher in water than that in sediment and biota. ANOSIM results showed that the different environmental media exhibit significant differences in MP characteristics (e.g., color, shape, and polymer). The ARIMA model predicted that Sanggou Bay and Hangzhou Bay have a higher potential for significantly increasing MP contamination in the future. The highest hazard index (HI) values for water, sediment, and biota were respectively reported at Jiaozhou Bay (18,844.16), Bohai Bay (11,485.37), and Dongshan Bay (48,485.11). The highest values for the ecological risk index (RI) in water, sediment, and biota were detected at Beibu Gulf (6,129,559.02), Haikou Bay (2229.14), and Dongshan Bay (561,563.05), respectively. Overall, this framework can be used at different scales and in different environments, which makes it useful for understanding and controlling MP pollution in the ecosystem.

Vibrio sinus sp. nov., a marine bacterium isolated from coastal seawater.

A Gram-straining-negative, facultatively anaerobic, motile by means of a polar flagellum and rod-shaped marine bacterium, designated S4M6T, was isolated from surface seawater collected in Dongshan Bay (Fujian, PR China). Phylogenetic analysis based on 16S rRNA genes, phylogenomic analysis of single-copy gene families and whole genome data indicated that S4M6T represented a member of the genus Vibrio. The closest phylogenetic relatives of S4M6T were Vibrio marisflavi CGMCC 1.8994T (97.8 % 16S rRNA gene sequence pairwise similarity), Vibrio variabilis LMG 25438T (96.9 %), Vibrio gangliei SZDIS-1T (96.2 %) and Vibrio aestivus M22T (96.1 %). The growth of S4M6T occurred at 15-35 °C (optimum 28 °C), pH 4.0-9.0 (optimum 5.0-7.0) and in the presence of 2-5 % (w/v) NaCl (optimum 3 %). The predominant fatty acids (>10 %) are C16 : 0, summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) and summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c). The DNA G+C content of the assembled genomic sequences was 43.4 % for S4M6T. Average nucleotide identity (ANI) values between S4M6T and the reference species were lower than the threshold for species delineation (95-96 %); in silico DNA-DNA hybridization further indicated that S4M6T had less than 70 % similarity to its relatives. On the basis of the polyphasic evidence, strain S4M6T is proposed to represent a novel species of the genus Vibrio, for which the name Vibrio sinus sp. nov. is proposed. The type strain is S4M6T (= KCTC 92312T= MCCC 1K06167T).

Study of Ra desorption processes in an estuary system with high-turbidity at the Southeast China

Radium (Ra) isotopes are extensively used as geochemical tracers for studying water mass mixing and submarine groundwater discharge in marginal and coastal seas. However, river-borne particles and seafloor sediments are an important source of Ra in marine systems due to Ra desorption. Therefore, it is necessary to study the desorption behaviors of Ra isotopes in river sediment or suspended particles. Here, the desorption behaviors of four Ra isotopes (223Ra, 224Ra, 226Ra, and 228Ra) in the Zhangjiang River sediments were investigated by a series of designed variable-controlling experiments in the laboratory. Within the designed salinity range, desorption amounts of Ra isotopes increased with increasing salinity, and when the salinity was greater than 15 ppt, Ra desorption reached an equilibrium state. Overall, desorption of Ra isotopes increased with the decrease of particle grain size, however, the desorption fractions of 224Ra and 228Ra decreased with decreasing particle size due to the increase of original Ra activities in smaller sediment particles. In the experiments, we found that two sediment samples with similar mean grain size (3.8 μm and 3.3 μm) and similar grain size distributions had significantly different Ra desorption under the same conditions. The results of mineral composition analysis based on X-ray diffraction showed that these two samples had different percentages of kaolinite, quartz, and plagioclase, which indicated that the mineral composition of particles had an important effect on Ra isotope desorption. In conclusion, salinity, particle grain size, and mineral composition all had significant effects on Ra desorption behaviors of sediment particles. Based on the above desorption experiments, the desorbed fluxes of four Ra isotopes from river-borne sediments to the Dongshan Bay were estimated to be (5.95 ± 1.47) × 107 Bq yr−1 for 223Ra, (1.95 ± 0.27) × 109 Bq yr−1 for 224Ra, (2.73 ± 0.47) × 108 Bq yr−1 for 226Ra, and (1.26 ± 0.20) × 109 Bq yr−1 for 228Ra, respectively.