The characterization, expression and activity analysis of three superoxide dismutases in Eriocheir hepuensis under azadirachtin stress.

Superoxide dismutase (SOD) can effectively eliminate of excess ROS, which causes oxidative damage to lipids, proteins, and DNA. In this study, we cloned the CuZn-SOD, cMn-SOD1, and cMn-SOD2 genes in Eriocheir hepuensis, and found that the coding sequence (CDS) lengths were 627 bp, 861 bp and 1062 bp, which encoded 208, 286, and 353 amino acids, respectively. Phylogenetic analysis indicated that all SOD genes were evolutionarily conserved, while cMn-SOD2 had an extra gap (67 amino acids) in the conserved domain compared with cMn-SOD1 without huge changes in the tertiary structure of the conserved domain, suggesting that cMn-SOD2 may be a duplicate of cMn-SOD1. qRT-PCR showed that the three SOD genes were widely expressed in all the tested tissues, CuZn-SOD and cMn-SOD1 were mostly expressed in the hepatopancreas, while cMn-SOD2 was mostly expressed in thoracic ganglia. Under azadirachtin stress, the oxidation index of surviving individuals, including the T-AOC, SOD activity, and MDA contents increased in the early stage and then remained steady except for a decrease in MDA contents in the later stage. qRT-PCR showed that the three SOD genes displayed the same trends as SOD activity in surviving individuals, and the highest expressions of CuZn-SOD in the hepatopancreas, heart, and gill were 14.16, 1.41, and 30.87 times that of the corresponding control group, respectively. The changes were 1.35, 5.77 and 3.33 fold for cMn-SOD1 and 1.62, 1.71 and 1.79 fold for cMn-SOD2, respectively. However, the activity and expression of SOD genes in dead individuals were lower than that observed in surviving individuals. These results reveal that SOD plays a significant role in the defence against azadirachtin-induced oxidative stress.

Cloning and expression of three heat shock protein genes in the gills of Cherax quadricarinatus responding to bacterial challenge.

Cherax quadricarinatus is seriously affected by multiple types of pathogens, including bacteria and viruses, and has been widely transplanted around the world. Heat shock proteins (Hsps) are a group of molecular chaperones that play important roles in promoting the proper refolding and blocking the aggregation of denatured proteins. In this study, CqHsp60, CqHsp70 and CqHsp90 from C. quadricarinatus were cloned, and their expression patterns were analysed. The CDS (coding sequence) lengths of the CqHsp60, CqHsp70 and CqHsp90 genes were 1731 bp, 1932 bp and 2199 bp, encoding 576, 643 and 732 amino acids, respectively. CqHsp60 was 99.13%, 98.78% and 88.63% identical to the corresponding sequences of Cherax cainii, Cherax destructor and Eriocheir sinensis, respectively. CqHsp70 showed 99.84%, 92.73% and 91.58% identity to the corresponding sequences of C. cainii, C. destructor and E. sinensis, while CqHsp90 was 98.25%, 98.51% and 91.41% identical with those of C. cainii, C. destructor and E. sinensis, respectively. The expression patterns of the three CqHsps were different between males and females. CqHsp60 and CqHsp70 exhibited the highest expression in the hepatopancreas of males and the gonads of females, and CqHsp90 presented the highest expression in the gonads of males and hepatopancreas of females. After pathogenic inoculation, the death trend of C. quadricarinatus at different time points was the same in association with different pathogens, with most deaths occurring within 6 h post-inoculation. The trend of CqHsp transcription at different time points was the same among the groups treated with Vibrio alginolyticus, Vibrio parahemolyticus and Aeromonas hydrophila, exhibiting upregulation first and then downregulation. The expression of CqHsp60 and CqHsp70 in the gills of living C. quadricarinatus was less than 3.5 times that in the PBS group, but in the gills of dead C. quadricarinatus under A. hydrophila inoculation, its expression was more than 5-9 times that in the PBS group. CqHsp90 expression changed dramatically in the V. alginolyticus, V. parahemolyticus and A. hydrophila groups, in which it exceeded 50 times the level in the PBS group. These results indicated that CqHsps could induce the activation of the immune system within a short time and that CqHsp90 could be used as a more effective molecular biomarker than CqHsp70 and CqHsp60 in a pathogenic bacterium-polluted environment.

Effects of intensive oyster farming on nitrogen speciation in surface sediments from a typical subtropical mariculture bay.

The spatial-temporal distributions of various nitrogen (N) species in surface sediments were examined in a typical subtropical mariculture bay (Maowei Sea) in the northern Beibu Gulf to assess the impact of intensive oyster culture activities on sedimentary N speciation. The results indicated that the mean contents of total nitrogen (TN), extractable (labile) nitrogen (LN) and residual nitrogen (RN) in the surface sediments were 33.3 ± 15.5 µmol g-1, 13.8 ± 1.3 µmol g-1 and 19.5 ± 15.0 µmol g-1, respectively, which lacked significant seasonal variability (P > 0.05). Four forms of LN, namely ion extractable form (IEF-N), weak acid extractable form (WAEF-N), strong alkali extractable form (SAEF-N) and strong oxidant extractable form (SOEF-N) were identified based on sequential extraction. SOEF-N was the dominant form of LN, accounting for 67.8 ± 2.5 % and 63.7 ± 5.9 % in summer and winter, respectively. Spatially, the contents of sedimentary TN, LN, RN, WAEF-N and SOEF-N in intensive mariculture areas (IMA) were significantly higher than those in non-intensive mariculture areas (NIMA) during summer (P < 0.05). Stable nitrogen isotope (δ15N) mixing model revealed that shellfish biodeposition was the predominant source of sedimentary TN in IMA with a contribution of 67.8 ± 23.0 %, approximately 5.4 times that of NIMA (12.6 ± 3.3 %). Significant positive correlations (P < 0.05) were observed between most forms of N species (WAEF-N, SOEF-N, LN and RN) and shellfish-biodeposited N in the surface sediments during summer, indicating that intensive oyster farming greatly enhanced sedimentary TN accumulation.

Comparative assessment of the environmental pollution and marine economic growth of Guangxi and China by using the environmental Kuznets curve fitting model.

This study examined the nexus between per capita gross ocean product (GOP) growth and total nitrogen (TN), total phosphorus (TP), and chemical oxygen demand (COD) discharged from land-based sources in Guangxi and China. Multiple pollution indicators, such as red tide area (RTA), seawater quality area (SWQA), and eutrophication area (EA), were used as marine environmental quality indicators, and annual time series data during the period 2010-2019 were employed. The data were analyzed using the environment Kuznets curve fitting model. Results showed that the average annual growth rates of the GOP and gross domestic product (GDP) of China were 9.88% and 10.79%, respectively, and those of Guangxi were 13.62% and 10.02%, respectively. The average annual GOP ratio in GDP for Guangxi and China was 6.59 and 9.47, respectively. The marine tertiary industry was the most dominant marine industry; it accounted for 41.12-50.01% (mean: 46.12%) of Guangxi's GDP and 47-60% (mean: 52.47%) of China's GDP. The TP, COD, SWQA, and EA of Guangxi and the TP, TN, COD, SWQA, and EA of China displayed inverted U-shaped GOP growth. These findings indicate that the marine economic growth and marine environmental quality of Guangxi and China are harmonious. However, TN increased synchronously with marine economic growth in Guangxi. Therefore, the industrial structure must be further optimized, pollutant discharge management must be strengthened, and the harmonious development of Guangxi's marine economy and marine environment needs to be promoted.

Spatiotemporal distributions of poorly-bound heavy metals in surface sediments of a typical subtropical eutrophic estuary and adjacent bay.

The toxicity of heavy metals is dependent on their bioavailability. This study explored the relationship existing among sedimentary nutrients such as bulk nitrogen (TN) and phosphorus (TP), organic carbon (OC), water column chlorophyll-a (Chl-a) and the poorly-bound fraction of sedimentary heavy metals (Cd, Ni, Zn, Cu, Pb and Cr) in the Dafengjiang River Estuary and adjacent Sanniang bay in 2017 and 2018. Results showed that the texture of the surface sediments was dominated by coarse sand, while sedimentary organic matter was dominated by marine phytoplankton and mariculture biodeposits. Surprisingly, concentrations of poorly-bound heavy metals in sediments were relatively high. The average contents of Cd and Ni did not vary both spatially and temporally, Cu and Pb only varied spatially, Cr varied both spatially and temporally, while Zn only varied temporally. Significant positive correlations occurred between sedimentary TN, TP, and OC, including water column Chl-a and poorly-bound heavy metals in sediments. As sediments are important sources of nutrients for primary productivity, the results of this study suggest that the remobilization of sequestered poorly-bound heavy metals in surface sediments deposited in shallow eutrophic estuaries and coastal waters enriched by labile organic matter can enhance by nutrients. The relationship between the poorly-bound heavy metals and nutrients in surface sediments and water column Chl-a is concerning and requires further in-depth investigation. This is because estuaries are economically important ecosystems rich in bioresources, characterized by dynamic biogeochemical conditions.

Contamination and ecological risk assessment of heavy metals, and relationship with organic matter sources in surface sediments of the Cross River Estuary and nearshore areas.

Chemical speciation of heavy metals (Zn, Pb, Cu, and Cd) was studied to evaluate the contamination status and associated risks and to constrain the sources of heavy metals in relation to sedimentary organic matter (OM) sources in surface sediments of the Cross River Estuary (CRE) and nearshore areas surrounded by a degrading mangrove ecosystem (typical C3 plants). The contamination factor (CF) and geo-accumulation (Igeo) indicated that Cd and Zn were the most polluted heavy metals. High percentages of Zn (63.78%), Pb (64.48%), Cd (76.72%) and the considerable amount of Cu (48.57%) in non-residual fractions indicated that these heavy metals are bioavailable. Cd showed moderate to high ecological and bioavailability risk based on the ecological risk (Er) and risk assessment code (RAC). Significant positive correlations occurred among the heavy metals, fine-grained sediments, and sedimentary OM from terrestrial C3 sources. These correlations, together with high percentages of heavy metals in the oxidizable fraction (~33-50%), indicated that the erosive washout of OM and fine sediments ladened with heavy metals from the adjoining degraded mangrove ecosystem contributed significantly to the increased contents of heavy metals in surface sediments of the study area.

Importance of ammonia nitrogen potentially released from sediments to the development of eutrophication in a plateau lake.

Sedimentary nitrogen (N) in lakes significantly influenced by eutrophication plays a detrimental role on the ecological sustainability of aquatic ecosystems. Here, we conducted a thorough analysis of the importance of N potentially released from sediments during the shift of "grass-algae" ecosystem in plateau lakes. From 1964 to 2013, the average total amount of sedimentary potential mineralizable organic nitrogen (PMON) and exchangeable N in whole Lake Dianchi were 5.50 × 103 t and 3.44 × 103 t, respectively. NH4+-N was the main product (>90%) of sedimentary PMON mineralization. The PMON in sediments had great release potential, which tended to regulate the distribution of aquatic plants and phytoplankton in Lake Dianchi and facilitated the replacement of dominant populations. Moreover, NH4+-N produced by sedimentary PMON mineralization and exchangeable NH4+-N have increased the difficulty and complexity of ecological restoration in Lake Dianchi to a certain extent. This study highlights the importance of sedimentary N in lake ecosystem degradation, showing the urgent need to reduce the continuous eutrophication of lakes and restore the water ecology.

Heavy metals speciation in surface sediments of the Cross River Estuary, Gulf of Guinea, South East Nigeria.

The speciation of heavy metals (Ni, Cr, Cu, Zn, Pb, and Cd) was studied in surface sediments of the Cross River Estuary (CRE), Gulf of Guinea, South East Nigeria. Pb (~56 %), Cd (~71 %), Zn (~67 %), and Cr (~76 %) were mainly available in non-residual phases, suggesting potential bioavailability. High contents of Ni and Cu in residual phase indicated immobilization of these metals in aluminosilicate minerals. Cd was the most polluted heavy metal with the highest bioavailability risk. Bayesian Network model results revealed that sedimentary organic carbon (OC) from terrestrial C3 plants controlled the contents and variability of Pb and Zn, while the input of terrestrial soil OC strongly influenced Cu and Ni. However, Cd and Cr were dominantly influenced by sediment pH, while Ni was mainly influenced by sediment salinity. Strong interdependency between Cd and total nitrogen (TN) suggested that nitrogen might increase Cd bioavailability upon release from sediments.

Sources, burial flux and mass inventory of black carbon in surface sediments of the Daya Bay, a typical mariculture bay of China.

The contents of chemothermal oxidation (CTO)-derived black carbon (BC) and organic carbon (OC) and their stable isotopes (δ13CBC and δ13COC), including major elemental oxides, and grain sizes were measured to constrain the sources, burial flux, and mass inventory of BC in surface sediments of the Daya Bay. Surface sediments were mainly clayey silt (>90%) and contained 0.28-1.18% OC and 0.05-0.18% BC. Fossil fuel emission and physical erosion contributed to the sedimentary BC sources. High BC/OC ratio (6-30%), burial flux (154.88-922.67 µg cm-2 y-1), and mass inventory (22-34 Gg y-1) of BC in the upper 5 cm of surface sediments indicated that the Daya Bay is a significant sink of BC. The high accumulation of BC in sediments is attributed to a strong affinity to fine-grained sediments due to the enrichment of muddy biodeposits excrements from the cultured species in the bay.

Historical changes of sedimentary P-binding forms and their ecological driving mechanism in a typical "grass-algae" eutrophic lake.

With the transformation of lake ecosystem from "clear water" to "turbid water", the residual phosphorus (P) accumulated in sediments may slow down the process of aquatic ecological restoration, and the related mechanisms are complex and need to be better understood. In this study, high-resolution systematic investigation and analysis of P-binding forms in the sediments showed that Lake Dianchi, the largest plateau lake in Southwest China, was enriched with NaOH-rP, HCl-P and Res-P, but depleted in NH4Cl-P, BD-P and NaOH-nrP. The BD-P, NaOH-nrP and NaOH-rP were the main contributors to potential P release from sediments, while the release potential of NH4Cl-P was relatively weak (<1%). When the external P loading gradually decreased, the internal P loading of Lake Dianchi was estimated to be 522 mg P/(m2•a) in the past 30 years. The succession of "grass-algae" type in Lake Dianchi coincided with reduced absorption and transformation of potential mobile P and decreased accumulation of stable P, especially the Res-P. Meanwhile, the temporal variation of potential mobile P was a good predictor of ecological degradation and reduced ecosystem sustainability in Lake Dianchi.

Organophosphorus flame retardants (OPFRs) in the seawater and sediments of the Qinzhou Bay, Northern Beibu Gulf: Occurrence, distribution, and ecological risks.

The occurrence, distributions, and ecological risks of 11 organophosphate flame retardants (OPFRs) were investigated in the seawater and sediment samples from the Qinzhou Bay. The Σ11OPFRs in the surface seawater and sediments ranged from 150 to 885 ng/L and from

Influence of sedimentary organic matter sources on the distribution characteristics and preservation status of organic carbon, nitrogen, phosphorus, and biogenic silica in the Daya Bay, northern South China Sea.

Surface sediment samples were collected from Daya Bay in October 2018, and analyzed for total organic carbon (OC), total nitrogen (TN) and their stable isotopes (δ13C and δ15N), total phosphorus (TP), biogenic silica (BSi), sediment textures and specific surface area (SSA). The primary objective was to evaluate the influence of mariculture/aquaculture on the distribution characteristics of organic matter (OM), and preservation status of OC, TN, TP, and BSi in sediments. The average δ13C and δ15N values, and OC/TN ratios were -21.27‰, 6.74‰, and 8.90, respectively. Monte Carlo simulation results revealed that mariculture/aquaculture biodeposits accounted for >40% of the buried OM at sites where the breeding rafts and cages are located, whereas marine OM increased gradually to the open sea. Terrestrial OM was generally low accounting for 17% by average. The contents and distribution characteristics of biogenic elements were more influenced by mariculture/aquaculture and primary productivity than sediment textures. Lower OC/SSA (0.3-1.2 mg OC/m2), TN/SSA (~0.05-0.18 mg TN/m2), and TP/SSA (0.02-0.04 mg TP/m2) loadings indicated that increased sequestration of labile OM in a coastal bay could contribute to significant degradation of recalcitrant OM in sediments with significant loss of P relative to OC. Nitrogen contamination in surface sediments was due to increased injection of aquaculture biodeposits, and may pose a detrimental effect on the ecological sustainability of the bay. Higher BSi/SSA loadings (0.9-1.7 mg BSi/m2) revealed that BSi was more preserved, and that BSi-based proxy could be used for paleo-productivity studies. However, such preservation may induce adverse dissolved silicate limitation in a bay perturbed by eutrophication. Fine-grained sediments (clay and silt) accounted for >77% of the sediment texture types with higher SSA, and while controlling the contents of biogenic elements under given depositional conditions were not the main determining factors of OC, TN, TP, and BSi preservation.

Influences of phosphorus concentration and porewater advection on phosphorus dynamics in carbonate sands around the Weizhou Island, northern South China Sea.

A series of flow-through reactor experiments were undertaken to assess the potential effect of porewater advection and dissolved inorganic phosphorus (DIP) concentration on benthic DIP dynamics in permeable sediments collected from the Weizhou Island, northern South China Sea. The flux of DIP ranged from -0.13 to 0.05 mmol m-2 h-1, and the reversal from DIP efflux to influx occurred when the DIP concentration reached a threshold. DIP release from the sediment into the seawater peaked at intermediate advection rate, which perhaps provide optimum conditions for DIP release related to CaCO3 dissolution. Phosphorus limitation in seawater could be relieved by DIP release from the sediment, and CaCO3-bound P in carbonate sands may play a major role in benthic DIP release and decrease in the molar nitrogen/phosphorus ratio in seawater around the Weizhou Island.

Spatiotemporal variations of biogenic elements and sources of sedimentary organic matter in the largest oyster mariculture bay (Maowei Sea), Southwest China.

China is the largest mariculture producer in the world, but detailed information on the spatiotemporal variations of biogenic elements and sources of sedimentary organic matter (SOM) via mariculture is limited. The primary objective of this study was to assess the influence of mariculture on the origin of SOM in relation with biogenic elements and geochemical paramaters due to the importance of SOM as a potential source of nutrients and energy in coastal marine environments. Surface sediments from the Maowei Sea were collected in August (summer) and December (winter), 2016 for grain size, total organic carbon (TOC), total nitrogen (TN), organic phosphorus (OP), biogenic silica (BSi), δ13C and δ15N analyses. Significant correlation (p < 0.01) was observed between TOC and TN in summer and winter respectively, indicating that they have common source in both seasons. The spatiotemporal distributions of TOC, TN, OP and BSi were influenced by the sources and distribution of SOM, grain sizes and hydrodynamic conditions in the Maowei Sea. The overall ranges of δ13C (-26.86‰ to -23.01‰) and δ15N (2.54‰ to 9.82‰) and C/N ratio (5.83 to 18.67) showed that SOM is derived from mixed sources. The δ13C and δ15N-based three-end-member mixing model results revealed that >40% of the deposited SOM originates from terrestrial source during two seasons. The SOM from shellfish mariculture was seasonal, mainly deposited in the intensive mariculture areas, and its proportions were only higher than contributions from marine plankton in summer. Generally, this study indicates that shellfish biodepositions can significantly influence the cycle of carbon and other biogenic elements in the intensive mariculture areas. Nevertheless, the overall dominance of terrestrial and marine SOM suggests that the sources of SOM and factors influencing carbon cycling in the Maowei Sea do not exclusively depend on the intensity of mariculture activities.

Compositions and spatio-temporal distributions of different nitrogen species and lability of dissolved organic nitrogen from the Dafengjiang River to the Sanniang Bay, China.

Field investigations and incubation experiment were carried out in the Dafengjiang River (DFJR) and Sanniang Bay (SNB) surface water from September 2017 to July 2018 to study the composition and spatio-temporal distributions of different nitrogen (N) species, lability of dissolved organic N (DON), and contributions of different N species from the DFJR to the dissolved inorganic N (DIN) level in the SNB. The spatio-temporal distributions of different N species exhibited significant seasonal variation (p < 0.05). The average contribution of DIN, DON, and particulate nitrogen (PN) to TN was 31.91%, 46.57%, and 21.52%, respectively. Comparatively being the dominant form of N in the study area, the average lability of DON across the incubation sites D1, D5 and D7 ranged from 72%-79%. DIN, DON, and PN from the DFJR respectively contributed to 55.95%, 7.03%, and 5.63% of water quality in the SNB.

Bulk sedimentary phosphorus in relation to organic carbon, sediment textural properties and hydrodynamics in the northern Beibu Gulf, South China Sea.

Bulk sedimentary phosphorus (P) is studied to evaluate its source, distribution, preservation and enrichment in relation with organic carbon (OC), sediment textures and moisture contents in the northern Beibu Gulf. Approximately 80% of surface sediments in the investigated sites were composed of coarse sandy texture (>63 µm). Total P (TP), inorganic P (IP) and organic P (OP) contents were lower to medium range compared to the levels reported for other marginal seas. Sedimentary OC and P were derived from mixed sources, with high terrestrial influence in the coastal areas (molar OC/OP ratios >250:1). The distribution of P corroborated with the variation tendency of fine-grained sediments, moisture contents and OC. Both IP and OP may significantly influence the trophic state of seawater if released from surface sediments. Influenced by hydrodynamics, frequent resuspension and high abundance of sand, TP is less preserved, and shows low to moderate enrichment in surface sediments.

Submarine groundwater discharge and its implication for nutrient budgets in the western Bohai Bay, China.

Submarine groundwater discharge (SGD) supplies substantial quantities of nutrients from land to oceans. However, SGD and associated nutrient fluxes have long been ignored in Bohai Bay, which is subjected to the serious environmental problem. Here, we investigated the concentrations of radon (222Rn) and nutrients in groundwater and surface water in the western Bohai Bay during May 2017. The flushing time in the bay was estimated to be 38.8-58.3 days based on tidal prism model. The SGD flux was estimated to be 7.3 ± 4.8 cm d-1 based on 222Rn mass balance model. The SGD associated nutrient fluxes were estimated to be (6.3 ± 4.1) × 107 mol d-1 for dissolved inorganic nitrogen (DIN), (1.2 ± 0.8) × 106 mol d-1 for dissolved inorganic phosphorus (DIP) and (7.5 ± 4.9) × 107 mol d-1 for dissolved inorganic silicon (DSi). By establishing nutrient budgets, we found that SGD was a major source, contributing 80.8% of all source for DIN, 90.7% of all source for DIP and 78.4% of all source for DSi into the western Bohai Bay. This study shows that SGD associated nutrient fluxes may have significant impact on nutrient budgets in the western Bohai Bay.

Geochemical discrimination of bulk organic matter in surface sediments of the Cross River estuary system and adjacent shelf, South East Nigeria (West Africa).

Knowledge of the sources, distribution and fate of organic matter (OM) in estuarine and adjacent shelf sediments are important for the understanding of the global biogeochemical cycles. Bulk organic carbon (C-org), total nitrogen (TN), biogenic silica (BSi), stable carbon (δ13C-org) and nitrogen (δ15N) isotopes, and sediment grain sizes were measured to study the spatial distributions and sources of sediment OM in the Cross River estuary system (CRES) and adjacent shelf. Surface sediments in the CRES were composed of clayey silt and sandy silt, while the adjacent shelf sediments were mainly silty sand. The range of the studied parameters was -28.79‰ to -22.20‰ for δ13C-org, -1.32‰-6.31‰ for δ15N, 6.7-29.2 for C-org/N ratios, 0.08%-0.33% for TN, 0.24‰-0.74‰ for BSi, and 0.47%-5.28% for C-org, and their spatial distributions showed a general decreasing trend in both the terrestrial and estuarine OM from the riverine regions to the adjacent shelf. Based on the three-end-member mixing model using the δ13C and δ15N isotopic values, ~58.01 ±â€¯15.32% of sediment OM are derived from terrestrial sources dominated by C3 vascular plants, while ~26.34 ±â€¯9.71% are attributed to estuarine sources dominated by aquatic macrophytes, and ~15.65 ±â€¯12.37% for marine plankton source. Other sources of OM identified included soils underlain C3 vascular plants and agricultural farms enriched with N, sewage, and petroleum hydrocarbons. The relationship between C-org vs. BSi, and the atomic BSi/Corg ratios suggested that diatoms also play an important role in OM sequestration in surface sediments of the CRES and adjacent shelf. The correlations of the δ13C-org and δ15N isotopic values vs. C-org/N ratios resulted in scatter plots, indicating that the distributions of sediment OM in the CRES and adjacent shelf are influenced by post depositional processes, fixed inorganic N adsorbed on fine-grained sediments, microbial degradation, as well as sediment grain size.

Phosphorus chemical speciation and seasonal variations in surface sediments of the Maowei Sea, northern Beibu Gulf.

This study presents the distribution, seasonal variations and factors influencing phosphorus (P) forms in surface sediments from the Maowei Sea. P forms were measured using the sequential extraction (SEDEX) procedures. Inorganic P (IP) was the predominant chemical form of total P (TP). Fe-bound P (FeP) was the main IP form. Sediment particle sizes, organic matter distribution, terrestrial input and aquaculture activity were responsible for the seasonal variations of different forms of P in sediment. In summer, the average proportions of P fractions in TP followed the order of organic P (OP) > Fe-P > authigenic P (CaP) > detrital P (De-P) > exchangeable P (Ex-P); in winter, the corresponding order was OP > Fe-P > De-P > Ca-P > Ex-P. The potential bio-available P accounted for 71.1 ±â€¯4.9% and 70.6 ±â€¯6.3% of TP in summer and winter, respectively. Sedimentary organic matter mainly came from land-based sources in winter.