Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

The long-term spatiotemporal changes of surface biogenic elements in the Changjiang River Estuary and adjacent waters during the summer of 2008–2016 were analyzed in this study.The concentrations of dissolved inorganic nitrogen(DIN),soluble reactive phosphate(PO_(4)^(3−))and silicate(SiO_(3)^(2−))were generally stable,with a slight decrease of DIN and PO_(4)^(3−),and a slight increase of SiO_(3)^(2−),which mainly occurred in the estuarine waters.The grey correlation analysis was carried out between biogenic elements and chlorophyll a(Chl-a).Results showed that compared with the absolute values of biogenic elements,the correlations between the concentration ratio of nitrogen to phosphorus(N/P),ratio of silicon to nitrogen(Si/N)and Chl-a were closer,indicating the important influence on phytoplankton by the structure of biogenic elements.The study area was generally in a state of potential P limitation,and could have potential impact on the phytoplankton community,triggering the shift of red tide dominant species from diatoms to dinoflagellates.

Environmental significance of biogenic elements in surface sediments of the Changjiang Estuary and its adjacent areas

Biogenic elements and six phosphorus （P） fractions in surface sediments from the Changjiang Estuary and adjacent waters were determined to investigate the governing factors of these elements, and further to discuss their potential uses as paleo-environment proxies and risks of P release from sediment. Total organic carbon （TOC） and leachable organic P （Lea-OP） showed high concentrations in the estuary, Zhejiang coast and offshore upwelling area. They came from both the Changjiang River and marine biological input. Biogenic silicon （BSi） exhibited a high concentration band between 123 and 124°E. BSi mainly came from diatom production and its concentration in the inshore area was diluted by river sediment. Total nitrogen （TN） was primarily of marine biogenic origin. Seaward decreasing trends of Fe-bound P and Al-bound P revealed their terrestrial origins. Influenced by old Huanghe sediment delivered by the Jiangsu coastal current, the maximum concentration of detrital P （Det-P） was observed in the area north of the estuary. Similar high concentrations of carbonate fluorapatite （CFA-P） and CaCO3in the southern study area suggested marine calcium-organism sources of CFA-P. TOC, TN and non-apatite P were enriched in fine sediment, and Det-P partially exhibited coarse-grain enrichment, but BSi had no correlation with sediment grain size. Different sources and governing factors made biogenic elements and P species have distinct potential uses in indicating environmental conditions. Transferable P accounted for 14%-46% of total P. In an aerobic environment, there was low risk of P release from sediment, attributed to excess Fe oxides in sediments.

Relationship between biogeochemical features of biogenic elements and flocculation in the Changjiang Estuary

This paper reports the relationship between the biogeochemical characteristics of C. N. P and flocculation and settling of suspended materials in the Changjiang Estuary. Regional activities of bacteria and the plankton and biogeochemical processes at the water-particle interface under some environmental conditions are quite variable. This leads to the transition of material phase with speciation variation of elements C. N. P. in the transfer processes. Therefore, the composition and reactivity of particle surface and dissolved constituent are modified, affecting the stability of the particulate dispersion system. In summer, the concentration of NO3 and PO4 are positively correlated with turbidity, while the weight percentage of PON, POC and PP are negatively correlated with turbidity. When particles in the river move seaward, two zones can be distinguished: i) zone with maximum flocculation speed, in salinity 0. 1～2. 0 ;ii) zone with huge coagulating particles netting and high turbidity at the bottom, in salinity 2～11.The highest values of C/N in particles (or the low valley of C. E. C.of particle surface) appear in the two zones. These results demonstrate that the biogeochemical action is one of the major factors and mechanisms to dominate the flocculation of particles in the Changjiang Estuary.

Distribution and contamination of metals and biogenic elements in sediments from Zhifu Bay of the Yellow Sea,China

Metals and biogenic elements were analyzed from surface sediments of sixteen stations and a 32 cm core collected from Zhifu Bay in July 2009.High concentrations of biogenic silica（BSi）reflected the high diatom productivity in the Bay.Meanwhile,total organic carbon（TOC）in Zhifu Bay was mainly from terrestrial sources.All metals were lower than the marine sediment quality guidelines.Based on the vertical profiles of biogenic elements,there was a clear increase of TOC,total nitrogen（TN）,and total phosphate（TP）between1985 and 2000.TN concentrations decreased after the start of the operation of the sewage treatment plant in 1998;however TOC and BSi remained at high levels.Metal concentrations showed a general increase from the bottom to the top of the core.Most anthropogenic metals reached a maximum during 1996 and 2000,and decreased after the startup of the sewage plant;however,they have increased again recently.The results from correlation analysis and principal component analysis show that industrial pollution is the main source of Cd,Cr,Cu,Ni,Pb and Zn contamination in Zhifu Bay,and Yantai Port and ship transportation also contribute a lot to Cd,Cu,Hg,and Pb pollution.

Horizontal Flux of Biogenic Elements through PN Section in April 1994

The horizontal flux of biogenic elements through PN section in April 1994 was calculated in the present paper using output of the OPYC model, which is a very general global model solving the full primitive equations forced by the atmospheric wind stress, observed heat flux, freshwater flux and cloudiness including a sea ice model both poles with rheology. However, since it is a global model, its resolution is rather coarse, less than 1°×1° horizontally and only 1 layer on continental shelf and 7 layers in the Okinawa Trough. We reconstructed the velocity profiles by ocean current modes evaluated from the hydrographic data along PN section and then used it to determine the flux of biogenic elements with the data collected during the Japanese cruise K94-04. The results shown that the volume transport was about 33×10 12 cm 3/s consistent with the OPYC model output, the maximum nitrate and phosphate flux densities were right on the shelf margin at the depth of about 300 m with the total fluxes 1.95×10 5 and 0.15×10 5 mol/s, respectively, the maximum dissolved oxygen and total carbon dioxide flux densities were on the surface layer near western side of the shelf margin and in the thermocline near the eastern side of the shelf margin with the total fluxes 1.43×10 8 L/s and 0.69×10 8 mol/s,respectively, through PN section in April 1994.

Impact of the exceptionally high flood from the Changjiang River on the aquatic chemical distributions on the Huanghai Sea and East China Sea shelves in the summer of 1998

On the basis of the field observation in the Huanghai Sea and East China Sea in the summer of 1998, a rare event of exceptionally high discharge from the Changjiang River was described and how this high discharge altered water masses as well as chemical distributions on the shelves of the Huanghai Sea and East China Sea. The maximal extending ranges of the Changjiang diluted water and the nutrients in the freshwater from the Changjiang River were recorded for the first time. It was also found that there was a closed area with high oxygen and pH values in the offshore area of the southern Huanghai Sea and the northern East China Sea, indicating that the extensive spreading of nutrients due to the high discharge led to photosynthesis of phytoplankton mostly taking place in the offshore area far from the river mouth. The presence of ＂excess nitrogen＂ in almost all the northern East China Sea and the south of the Huanghai Sea suggests that these areas are potentially phosphorus-limited rather than nitrogen-limited, manifesting more like an estuarine ecosystem rather than a common marine ecosystem.

Terrestrial input and nutrient change reflected by sediment records of the Changjiang River Estuary in recent 80 years

A variety of environmental problems have been observed in the Changjiang River Estuary and adjacent coastal area, including eutrophication, harmful algal blooms（HABs）, and hypoxia in recent decades. Application of sedimentary biogenic element indicators on the study of paleoenvironment can reconstruct environmental evolution history of waters. Two 210Pb-dated cores were collected from the Changjiang River Estuary（S3） and adjacent coastal area（Z13）, and total organic carbon（TOC）, total nitrogen（TN）, biogenic silicon（BSi）, total phosphorus（TP） and phosphorus（P） species were analyzed. Three stages of environmental changes are deduced by the nutrient sedimentary records. First, nutrient concentration increased rapidly since the 1950 s, which attributed to agriculture development and overused chemical fertilizers. Second, nutrient concentration kept high and primary production began to promote during the 1960 s to 1980 s, while diatom abundance and proportion began to decline since the 1970 s, accompanied by reduced 23 Si O- concentration and flux from the river. Third, due to several dams and bridges constructed, river runoff and coastal hydrodynamic conditions reduced to a certain extent since the 1990 s, which aggravated the unbalance in nutrient structure. Multi-nutrient proxies in sediment can reflect the natural environm-ental changes as well as influence of human activities.