Daya Bay Research Articles

Distribution and co-occurrence networks of the bacterial community in sediment cores from the subtropical Daya Bay, China

The bacterial community plays an important role in biogeochemical cycles in marine sediment. However, little is known about the vertical profiles and co-occurrence patterns of bacterial community in sediment cores from the marine environment. In this study, five sediment cores were taken from a subtropical bay in China, heavily impacted by anthropogenic activities. The bacterial composition in sediment cores was investigated by using high-throughput sequencing of the 16S rRNA gene. A principal coordinates analysis and an adonis analysis of the operational taxonomic unit (OTU) compositions showed that spatial variation, rather than vertical variation, determined the bacterial structure in sediment cores. The bacterial complexity varied greatly across the five sediment cores, and the rare taxa played an important role in supporting the stability of the bacterial network. This study revealed that sediment properties and anthropogenic activities may induce a shift in the bacterial composition in sediment cores of a subtropical bay.

The anthropogenic effects on organic matter in sediment core based on Bayesian mixing model: a case study of Daya Bay.

Sediment is an important carrier of evidence about environmental evolution which receives huge volumes of organic material originated from both anthropogenic and natural sources. In this study, based on sedimentary chronology, the vertical trends of particle size distribution, total organic carbon (TOC), total nitrogen (TN), and their stable isotopes (δ13C, δ15N) in the sediment core of the nuclear power sea in southwest Daya Bay were analyzed, and the distribution characteristics and contribution ratios of different sources of organic matter in the sedimentary environment over the past 70years were resolved using a Bayesian mixing model (MixSIAR). TOC, TN, δ13C, and δ15N ranged from 0.89 to 1.56%, 0.09 to 0.2%, - 22.3 to - 20.6‰, and 4.38 to 6.51‰, respectively. The organic matter in the sediment is controlled by a mixture of terrestrial input and marine autochthonous, the proportion of organic matter from terrestrial sources increases, while that from marine sources decreases in the sediment core, which persists from 1960 to 2000, yet organic matter from marine sources still dominates. The first signs of increased primary productivity occurred in 1960, and it was primarily due to agricultural activity. After the 1980s, the rapid increase in population around Daya Bay, the construction of nuclear power plants, the rise of aquaculture, and the quick expansion of industrial bases were all major factors that changed the ecological environment of Daya Bay.

Anthropogenic influences on the sources and distribution of organic carbon, black carbon, and heavy metals in Daya Bay's surface sediments

The total organic carbon (TOC), total nitrogen (TN), black carbon (BC), δ13CTOC, δ15N, δ13CBC, grain size, and heavy metals of surface sediments collected from Daya Bay were determined to investigate the spatial distributions of these parameters and to evaluate the influences of human activities. Marine organic matter was found to constitute approximately 84.41 ± 7.70 % of these sediments on average. The western and northern regions of Daya Bay exhibited relatively fine grain sizes, weak hydrodynamic conditions, and high sedimentation rates, which favored the burial and preservation of organic matter. The high concentration of organic matter could be attributed to the influence of petroleum and aquaculture industries. Fossil fuels were the main source of BC. The enrichment factor (EF) and geo-accumulation index (Igeo) were used to evaluate the sources and pollution levels of heavy metals. The results revealed that the source and distribution of heavy metals were strongly influenced by human activities, resulting in moderate pollution levels across most regions of Daya Bay. A strong correlation was observed between the Igeo values of heavy metals and BC, TOC, TN, and mean particle grain size (Mz). This suggests that the ability of sediments in Daya Bay to enrich and adsorb heavy metals depends on the sediment grain size, the content and type of organic matter. Importantly, sediments in the inner bay of Daya Bay exhibited a greater capacity to impede the migration of heavy metals compared to those in the outer bay.

Neorhizobium turbinariae sp. nov., a coral-beneficial bacterium isolated from Turbinaria peltata.

Coral reef ecosystems are facing decline due to climate change, overfishing, habitat destruction and pollution. Bacteria play an essential role in maintaining the stability of coral reef ecosystems, influencing the well-being and fitness of coral hosts. The exploitation of coral probiotics has become an urgent issue. A short-rod shaped aerobic bacterium, designated NTR19T, was isolated in a healthy coral Turbinaria peltata from Daya Bay, Shenzhen, PR China. Its cells were Gram-negative, motile with a polar flagellum. The activities of catalase and oxidase were positive. Strain NTR19T grew at 10-41 °C (optimum, 28 °C), with NaCl concentrations of 0-4 % (w/v; optimum, 0.5 %) and at pH 5.0-9.5 (optimum, pH 7.0-7.5). The predominant fatty acids (>10 %) were summed feature 8 (57.6 %), C19 : 0 cyclo ω8c (12.6 %) and C16 : 0 (12.0 %). The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phospholipid and phosphatidylcholine. The major respiratory quinone was Q-10. The draft genome was 4.68 Mbp with 61.2 mol% DNA G+C content. In total, 4477 coding sequences were annotated and there were 64 RNA genes. The average nucleotide identity (ANI) and average amino acid identity (AAI) values between strain NTR19T and the related Neorhizobium species were 78.23-79.70% and 80.26-80.50 %, respectively. This strain encoded many proteins for the activities of catalase and oxidase in the genome. Strain NTR19T was clearly distinct from its closest neighbours Rhizobium oryzicola ACCC 05753T and Neorhizobium petrolearium ACCC 11238T with the 16S rRNA gene sequence similarity values of 96.86 and 96.36 %, respectively. The results of phylogenetic analysis, as well as ANI and AAI values, revealed that strain NTR19T belongs to Neorhizobium and was distinct from other species of this genus. The physiological, biochemical and chemotaxonomic characteristics also supported the species novelty of strain NTR19T. Thus, strain NTR19T is considered to be classified as a novel species in the genus Neorhizobium, for which the name Neorhizobium turbinariae sp. nov. is proposed. The type strain is NTR19T (=JCM 35342T=MCCC 1K07226T).

Neutrino oscillation bounds on quantum decoherence

We consider quantum-decoherence effects in neutrino oscillation data. Working in the open quantum system framework we adopt a phenomenological approach that allows to parameterize the energy dependence of the decoherence effects. We consider several phenomenological models. We analyze data from the reactor experiments RENO, Daya Bay and KamLAND and from the accelerator experiments NOvA, MINOS/MINOS+ and T2K. We obtain updated constraints on the decoherence parameters quantifying the strength of damping effects, which can be as low as Γij ≲ 8 × 10−27 GeV at 90% confidence level in some cases. We also present sensitivities for the future facilities DUNE and JUNO.

Applications of Environmental DNA (eDNA) in Monitoring the Endangered Status and Evaluating the Stock Enhancement Effect of Tropical Sea Cucumber Holothuria Scabra.

The tropical sea cucumber Holothuria scabra is naturally found in the Indo-West Pacific. However, due to their commercial value, natural H. scabra populations have declined significantly in recent years, resulting in its status as an endangered species. Surveys of H. scabra resource pose a challenge due to its specific characteristics, such as sand-burrowing behavior. To overcome this problem, our study established a convenient and feasible method for assessing H. scabra resources using environmental DNA (eDNA) monitoring technology. First, H. scabra-specific TaqMan primers and probe were designed based on its cox1 gene, followed by the development of an eDNA monitoring method for H. scabra in two separate sea areas (Xuwen and Daya Bay). The method was subsequently employed to investigate the distribution of H. scabra and assess the effects of aquaculture stock enhancement through juvenile releasing in the Weizhou Island sea area. The H. scabra eDNA monitoring approach was found to be more appropriate and credible than traditional methods, and a positive impact of stocking on H. scabra populations was observed. In summary, this is the first report to quantify eDNA concentration in a Holothuroidea species, and it provides a convenient and accurate method for surveying H. scabra resources. This study introduces novel concepts for eDNA-based detection of endangered marine benthic animals and monitoring their population distribution and abundance.

Investigation on the radioactivity levels of seawater, sediments, and biota in Daya Bay, China

ObjectiveTo investigate the radioactivity levels of seawater, sediments, and biota in the Daya Bay sea area, China, in order to establish the radioactivity baseline values, and provide basic data for the assessment of potential radiological risks that might result from the application of nuclear technology or human activities. MethodsSamples of seawater, sediments, and biota were collected from the Daya Bay sea area and analyzed. Their radioactivity baseline data were then compared with information from other regions in China and around the world reported in related literature. ResultsFor the seawater samples, the activity concentrations of natural radionuclide 40K were 9.9–10.4 Bq/L, while 238U, 226Ra, 210Pb, 137Cs, and 110Agm were below the minimum detectable activity (MDA). Regarding the sediment samples, the activity concentrations of 238U, 228Ra, 226Ra, 210Pb, 40K, and 137Cs were 38.1–40.4, 49.1−53.7, 32.6−38.6, 59−95, 590−650, and 0.48–0.88 Bq/(kg dry weight), respectively, while 110Agm was below the MDA. For the marine shrimps in the biota samples, the activity concentrations of 228Ra, 226Ra, 40K, and 137Cs were 1.14–2.75, 0.17−0.43, 63–76, and 0.038–0.045 Bq/(kg wet weight), respectively, while 238U, 210Pb, and 110Agm were all below the MDA. Furthermore, for the marine fishes in the biota samples, the activity concentrations of 228Ra, 226Ra, 210Pb, 40K, and 137Cs were 2.1–19.7, 0.32–3.78, <2.2–2.8, 59–70, and <0.007–0.026 Bq/(kg wet weight), respectively, while 238U and 110Agm were all below the MDA. 228Ra was found to be concentrated in Osteomugil ophuyseni with 19.7 Bq/(kg wet weight). ConclusionsThe radioactivity levels of seawater and marine sediments in the Daya Bay sea area are within the range of the normal background values. Osteomugil ophuyseni exhibited higher concentrations of 228Ra than other species in this study, while the other species in the biota show no significant difference in the radioactivity levels from data in relevant literature.

Spatial distribution and export of nutrients and metal elements in the subterranean estuary of Daya Bay

Spatial distribution and export of nutrients and metal elements in the subterranean estuary of Daya Bay

Using radium isotopes to evaluate the uncertainty of submarine groundwater discharge in the northeast and entirety of Daya Bay

Using radium isotopes to evaluate the uncertainty of submarine groundwater discharge in the northeast and entirety of Daya Bay

Coastal sediment heavy metal(loid) pollution under multifaceted anthropogenic stress: Insights based on geochemical baselines and source-related risks

Contamination and risk assessments generally ignore the potential bias in results caused by the variation of background values at different spatial scales due to the spatial heterogeneity of sediments. This study aims to perform quantitative source-ecological risk assessment via establishing geochemical baselines values (GBVs) of heavy metal(loid)s (HMs) in Daya Bay, China. Cumulative frequency distribution (CFD) curves determined the GBVs of 12.44 (Cu), 30.88 (Pb), 69.89 (Zn), 0.06 (Cd), 47.85 (Cr), 6.80 (As), and 0.056 mg kg−1 (Hg), which were comparable to the background values of Guangdong Province surface soils, and implied a potential terrestrial origin of the coastal sediments. Principal component analysis (PCA) and positive matrix factorization (PMF) identified three sources (F1: natural processes; F2: anthropogenic impacts; F3: specific sources) with contributions of 51.7%, 29.2%, and 19.1%, respectively. The source-specific risk assessment revealed an ecological risk contribution potential of 73.8% for the mixed anthropogenic sources (F2 + F3) and only 26.2% for natural processes. Cd and Hg were the priority management of metallic elements, occupying 63.5% and 72.5% of the contribution weights of F2 and F3, respectively, which showed multi-level pollution potentials and ecological risk levels. The spatial distribution patterns demonstrated the hotspot features of HM pollution, and priority concerns should be given to the management of marine traffic and industrial point source pollution in Daya Bay. The results of the study provide a scientific approach and perspective for pollution treatment and risk management in the coastal environment.

Microplastic Pollution and Its Potential Correlation with Environmental Factors in Daya Bay, South China Sea

Microplastics (MPs) have been given considerable attention due to their risk to aquatic organisms in marine environments. In this study, MPs’ abundance and their potential correlation with environmental factors were investigated from 26 sites in Daya Bay, South China Sea. The results showed that the abundance of MPs was 1.8–13.87 items/L in surface water and 190–823 items/kg (dry weight) in sediment. The most abundant shape of MPs in both water and sediment was fiber, the most abundant particle size was 0.5–1 mm and the most abundant color was transparent. In addition, the most common polymer type of MPs was polyethylene terephthalate (PET), followed by rayon (RY), polypropylene (PP), cellulose (CL) and polyethylene (PE). The abundance of MPs in sediment was significantly correlated with sediment organic N and C (p &lt; 0.05), while that in surface water had no significant correlation with the environmental factors except dissolved oxygen (p &gt; 0.05). A factor analysis showed that MPs in sediment might share similar sources with organic N and C, which were mainly from the autochthonous sedimentation of marine organisms, and MPs might sediment jointly with organic matter. In summary, this study reflects on MP pollution and the potential correlation with environmental factors, providing essential data for governmental agencies to formulate microplastic pollution control policies.

Prediction of supernova neutrino signals by detectors and its future challenges

Supernova neutrinos produced during a core collapse of a massive star, carries 99% of the energy produced during the violent phenomenon. These neutrinos are weakly interacting massive particles and can provide useful information for both particle physics (neutrino oscillations parameters) and astrophysics (explosion mechanism). This information can be used to explore physics beyond the standard model. Neutrinos escape from the supernova core hours before the light, so a neutrino signal providing information about supernova direction can enable early observation. The current generation of detectors, like, Super-Kamiokande (Super-K), Large Volume Detector (LVD), Borexino, Kamioka Liquid Scintillator Antineutrino Detector (KamLAND), and IceCube, as well as HALO, Daya Bay(reactor neutrino experiment) and NuMI Off-Axis νe Appearance experiment (NOvA), have the ability to detect only a few orders of magnitude of events and the next generation experiment like, Hyper-Kamiokande (Hyper-K), Deep Underground Neutrino Experiment (DUNE), and Jiangmen Underground Neutrino Observatory (JUNO) will have yet another order of magnitude in reach, as well as richer flavor sensitivity. This work will present a Monte Carlo based study using the SNOwGLoBES [1] package, which is used to estimate the event rate using folded fluxes, cross-sections, and detector smearing to determine mean expected neutrino interaction signals in multiple current and future detectors. A study is carried out for the calculation of core-collapse neutrino event rates in realistic detectors for different flux models, effects of different parameters on flux and its variation with time.

Shell accumulation on seabed due to suspended coastal oyster farming and effects on burrowing capacity of the polychaete Perinereis aibuhitensis

Mariculture of bivalves (e.g., mussels, scallops, and oysters) is developing rapidly in coastal waters. This process releases shell debris that can accumulate on the seabed under farms. The ecological consequences of shell accumulation on the bioturbation of benthic macrofauna, which play a key role in the biogeochemical processes of sediment, are not yet fully understood. Thus, it is necessary to quantify the shell debris that accumulated under bivalves farms and evaluate whether the shell debris hinders the burrowing capacity of macrofauna. Oysters are common bivalve species cultured worldwide. However, no data are available on shell accumulation due to oyster farming and its possible effects on the burrowing capacity of polychaetes. Thus, we conducted a preliminary study on shells debris accumulation under an oyster farm in Daya Bay, southern China, and assessed the effects of shell accumulation on the burrowing activity of the polychaete Perinereis aibuhitensis in a mesocosm experiment for 32 days. The results showed that oyster farming significantly (p &amp;lt; 0.05) increased the accumulation of shell debris under the farm. The amount of shell debris under oyster farm (6.0 ± 1.3 kg (dry weight (DW)) m-2 or 130.0 ± 24.7 g (DW) kg-1 dry sediment) was approximately two times that in a non-culture area (3.5 ± 0.9 kg (DW) m-2 or 74.9 ± 10.5 g (DW) kg-1 dry sediment). The presence of shell debris did not affect the survival of P. aibuhitensis in experiment, but the animals in sediment with shell added exhibited greater losses of body weight compared with those without, indicating that the presence of shell causes animals to expend more energy in burrowing. The numbers of burrowing holes were lower in sediment with shell debris added compared with those in sediment without shell addition throughout the experiment. Whereas, this does not due to the P. aibuhitensis in +Shell treatment were less active in terms of their burrowing activities. The lower numbers of holes in +Shell treatment was mainly due to P. aibuhitensis were unable to use surface areas where shells were present, the amount of area occupied by shell material physically prevented P. aibuhitensis from forming burrows in these locations. The hindering effects of shells on the burrowing activity of P. aibuhitensis would decrease as the shells degraded into debris. Therefore, we recommend using small shells when conducting “shell addition” bioremediation strategies to avoid the possible negative effects of shells on burrowing by polychaetes.

Impact of long-term operation of nuclear power plants on the marine ecosystem of Daya Bay

Based on the monitoring data of Daya Bay in 2011–2017, the impact of long-term operation of nuclear power plants (NPPs) on the marine ecosystem was accessed. 137Cs and 90Sr in seawater and sediment of Daya Bay decreased with time. The environmental half-lives of 137Cs and 90Sr in seawater, 137Cs in sediment were 7.1 a, 11.7 a and 13.9 a, respectively. The total dose rates of the marine organisms ranged from 230.5 to 853.9 nGy/h, lower than the ERICA screening benchmark (10 μGy/h). 210Po, 226Ra and 232Th were the main dose contributors. 137Cs and 90Sr contributed to ~0.01 %–~0.06 % of the total radiation. 137Cs contributed to <0.6 ‰ of the committed effective dose for humans. There were almost no radiation effects on the marine ecosystem of Daya Bay from NPPs before 2017. In the future, there will be no radiation risk for the long-term discharge of low-level radioactive waste to Daya Bay.

Response of zooplankton to warming in a low-salinity, eutrophic bay

Warming and eutrophication are universal threats to bay ecosystems. However, the response of zooplankton varies due to diverse environmental settings and species composition. As a long and narrow semi-enclosed bay with low salinity (18–27) in the East China Sea, Xiangshan Bay (XSB) is jointly affected by global warming and the thermal drainage, which makes it an appropriate region for ascertaining the response of zooplankton to warming under low-salinity background. We examined the long-term changes in the abundance, biomass and dominant species of large mesozooplankton (LMZ; >505 μm) over four decades in XSB, and found downward trends in the annual abundance and biomass, and the biomass peak shifting from summer to spring since 2010. In addition, the relative abundance of cold-temperate species decreased, while that of warm-temperate/warm-water species and small-sized zooplankton increased. The decreased LMZ abundance and biomass in XSB were supposed to be related to low gelatinization compared with the other semi-enclosed bays in China, Jiaozhou Bay (JZB) in the Yellow Sea and Daya Bay (DYB) in the South China Sea, where the LMZ biomass and abundance increased or fluctuated mainly linked to the increase in gelatinous zooplankton. Salinity, temperature, and nutrient concentration are important factors affecting gelatinization. By comparing the background salinity and magnitudes of temperature and nutrient increases among the three bays, we speculated that the lower salinity (XSB: 18–27, JZB: 30–32, DYB: 30–34) influenced by freshwater input of the Changjiang River might be a potential factor causing the low gelatinization in XSB, as the similar upward trends in both nutrient concentration and temperature were observed in the three bays. This study suggests that miniaturization with low gelatinization and a decrease in cold-temperate species were the main responses of zooplankton to warming in the low-salinity bay in the East China Sea, which may lead to a specific pelagic ecosystem evolution.

Submarine groundwater discharge and associated metal elements into an urbanized bay

In this study, geochemical tracers (radium isotopes) and heavy metals (Pb, Zn, Cd, Cr and As) were analyzed to derive the submarine groundwater discharge (SGD) and associated metal fluxes during four seasons in an urbanized bay (Daya Bay, China). Results showed that Pb and Zn were the main pollutants in bay water. SGD was found to exhibit an obvious seasonal trend (autumn > summer > spring > winter). Such seasonal patterns may be related to the hydraulic gradient between groundwater level and sea level, storm surges and tidal range. SGD was a dominant source of marine metal elements, contributing 19 %–51 % of the total inputs of metals into Daya Bay. The bay water was classified as slight pollution to heavy pollution, which could be linked to SGD-derived metal fluxes. This study provides a better understanding of the important role that SGD plays in metal budgets and ecological environments of coastal waters.

Improved Measurement of the Evolution of the Reactor Antineutrino Flux and Spectrum at Daya Bay.

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. In this Letter, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as the flux evolution with the ^{239}Pu isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted inverse-beta-decay spectrum from ^{239}Pu fission does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to ^{235}U fission is changed or the predicted ^{235}U, ^{238}U, ^{239}Pu, and ^{241}Pu spectra are changed in equal measure.

Bioremediation of propylbenzenes by a novel marine microalga Rhinomonas reticulata S6A isolated from Daya Bay: acute toxicity, growth kinetics and biodegradation performance

This study investigated the degradation characteristics of propylbenzenes (PBZs, including isopropylbenzene and n-propylbenzene), with high leakage risks and ecological hazards, by a newly isolated marine microalga named Rhinomonas reticulata S6A which is a promising candidate for eco-friendly bioremediation from marine. About 72% and 56% of n-PBZ and i-PBZ can be degraded after 7 days in culture. The acute toxicity of n-PBZ (96h - EC50 = 2.38 mg/L) was higher than that of i-PBZ (96h - EC50 = 3.65 mg/L). The growth inhibition kinetics of this strain were consistent with the Edwards model (R2 = 0.998) and Aiba model (R2 = 0.999). The optimal concentrations for the degradation of n-PBZ and i-PBZ were calculated to be 2.42 mg/L and 2.78 mg/L, respectively. The degradation trends of PBZs conformed to the zero-order kinetic model, and k increased with initial concentrations. The moderate increase in inoculation density could accelerate the degradation of PBZs, with the maximum specific growth rates (r) of 1.116/d (n-PBZ) and 1.230/d (i-PBZ) at the initial inoculation density of 104 cells/mL, while over-inoculation (initial microalgae density more than 105 cells/mL) was not conducive to the degradation of the pollutants. There is not much data on the biodegradation of PBZs in the aquatic environment, so it would be worthwhile to try to apply the new microalgae to explore the fate of PBZs.

Annual variation in domoic acid in phytoplankton and shellfish samples from Daya Bay of the South China Sea

Domoic acid (DA) is a well-known phycotoxin that causes amnesic shellfish poisoning (ASP) and is mainly produced by diatom species belonging to the genus Pseudo-nitzschia. An annual survey was conducted monthly over the period of September 2020 to August 2021 in Daya Bay of the South China Sea to investigate the dynamics of particulate and shellfish DA and their relationships with the abundance of Pseudo-nitzschia spp. and environmental parameters. Pseudo-nitzschia spp. was one of the most dominant phytoplankton taxa, and a Pseudo-nitzschia bloom occurred during the survey with the highest abundance of 1.91 × 106 cells L−1. DA was detected in almost all plankton samples with the highest value of 120.7 ng L−1, and high DA concentrations coincided with the abundant presence of Pseudo-nitzschia. DA is prevalent in Daya Bay throughout the year, with detection rates of 98.3%, 82.6%, and 82.6% in plankton samples, in-situ and purchased shellfish, respectively. Higher DA concentrations were detected in the scallop (Chamys nobilis), with the highest concentration of 5.34 µg g−1. High water temperature and low DSi:DIN ratio promoted the growth of Pseudo-nitzschia and DA production. The results suggest that the increasing nitrogen loading and silicate limitation during Pseudo-nitzschia blooms together with the increase in water temperature may increase the risk of DA contamination in Daya Bay.

Long-Term Variations of Biogenic Elements and Nutritional Status in Daya Bay, Northern South China Sea

This study explored the variations in the characteristics of the trophic structure of Daya Bay island waters over the last four decades based on the survey findings and research data on biogenic elements (dissolved inorganic nitrogen (DIN), NO2−, NO3−, NH4+, PO43−, and SiO32−) in Daya Bay during 1985–2021. At this time, the DIN concentration increased from 21.14 µg·L−1 to 558.42 µg·L−1 (26.41-fold increase), whereas the SiO32− concentration increased by only 3.6-fold. The PO43− concentrations attained a peak in 2004 and experienced a steady decline over the rest of the survey period. The fractions of NH4+, NO3−, and NO2− in DIN changed from 0.45, 0.40, and 0.15 in 1986 to 0.26, 0.74, and 0.003 in 2021, respectively. Overall, the mean values of NH4+, NO3−, and NO2− accounted for 45.2%, 42.5%, and 12.3%, respectively. The N/P(DIN/PO43−) ratio in Daya Bay increased from 28.08 in the 1980s to 51.63 in the 2010s. Meanwhile, the nutrient limitation conditions showed a gradual shift from N-limited to P-limited conditions. According to the nutrient quality index (NQI) analysis, the trophic state level of Daya Bay waters fell into the oligotrophic category 30 years ago (1985–2002, NQI &lt; 2), whereas it increased from the mesotrophic level in 2005 (NQI = 2.03) to the eutrophic level in 2019 (NQI = 3.33) over the last 20 years. The results based on the eutrophication index (EI) of Daya Bay waters were generally consistent with those based on the NQI, displaying that the trophic level of Daya Bay waters indicated an increasing trend from 2005 to 2019. Moreover, the assessment data in 2021 indicated a decrease in the NQI to 0.90, thereby attaining the oligotrophic level again. This may be related to the decrease in aquacultural area in the bay over the last two years. The correlation analysis among the DIN, PO43−, and nutrient levels of Daya Bay waters indicated that the input of nitrogen and phosphorus was the primary reason for the higher nutrient levels in the water bodies; among them, municipal sewage discharge, aquaculture, and atmospheric deposition from industry are the main factors for the over importation. This indicates that the changes in the biogenic element concentrations led to variations in the trophic structure and level of Daya Bay and may be attributed to population growth and the development of the seaside industry and agriculture in the region.