Long-term variation in nutrients in the South Yellow Sea in response to anthropogenic inputs.

Based on historical data from 1976 to 2019, the effects of anthropogenic activities on long-term changes in nutrients and their ecological effects in the South Yellow Sea were investigated. The dissolved inorganic nitrogen (DIN) concentrations increased continuously from 1990 until the mid-2000s, followed by a shift from an upward trend to a downward trend. The phosphate (PO4-P) and silicate (SiO3-Si) concentrations also showed obvious interannual variations throughout the study period. The concentrations of DIN, PO4-P and SiO3-Si have decreased significantly in recent decade and more. These changes mainly resulted from the reduction in terrestrial input, while the main reason for the decrease in DIN and PO4-P concentrations is the reduction in anthropogenic input. The long-term nutrient changes in the South Yellow Sea have potential ecological impacts on green tide features.

Storm-induced sediment resuspension in the Changjiang River Estuary leads to alleviation of phosphorus limitation.

This paper presents an incubation experiment with sediment cores from the Changjiang Estuary Mud Area (CEMA) to quantify the release of nutrients due to simulated resuspension. The results show that except for nitrate (NO3--N), phosphate (PO43--P), ammonium (NH4+-N), nitrite (NO2--N) and silicate (SiO32--Si) were released from the sediment to the overlying water, primarily due to desorption (P), dissolution (SiO32--Si) and mineralization (NH4+-N) with only minor direct contributions from the sediment pore water. The significant release of nutrients by resuspension and subsequent processes can alleviate the phosphorus and silicon limitation in water bodies, enhance the growth of phytoplankton, and thus promote the oxygen consumption and ultimately lead to hypoxia. The results of this study are highly relevant for many coastal areas in other parts of the world with large amounts of stored organic matter and nutrients in sediments and frequent perturbation by storm events.

The impact of giant jellyfish Nemopilema nomurai blooms on plankton communities in a temperate marginal sea.

This study focused on the bloom-developing process of the giant jellyfish, Nemopilema nomurai, on phytoplankton and microzooplankton communities. Two repeated field observations on the jellyfish bloom were conducted in June 2012 and 2014 in the southern Yellow Sea where blooms of N. nomurai were frequently observed. We demonstrated that the bloom was made up of two stages, namely the developing stage and the mature stage. Total chlorophyll a increased and the concentrations of inorganic nutrients decreased during the developing stage, while both concentrations maintained stable and at low levels during the mature stage. Our analysis revealed that phosphate excreted by growing N. nomurai promoted the growth of phytoplankton at the developing stage. At the mature stage, size compositions of microzooplankton were altered and tended to be smaller via a top-down process, while phytoplankton compositions, affected mainly through a bottom-up process, shifted to be less diatoms and cryptophytes but more dinoflagellates.

Long-term variations and influence factors of nutrients in the western North Yellow Sea, China.

This study investigated the long-term variations and compositions of nutrients and the associated controlling factors in the western North Yellow Sea on the basis of historical data. The NO3-N and DIN concentrations and N/P showed continuous increases over the past two decades, which were dominantly affected by riverine inputs, such as inputs from the Yellow River, Yalujiang River and Jia River and atmospheric deposition. However, due to human activities, such as dam construction in rivers and climate change, the SiO3-Si concentrations and Si/P ratios decreased before the early 1990s and then gradually increased. The vertical distributions of nutrients displayed higher concentrations at the bottom than those at the surface in summer, which was attributed to the combined influence of the thermocline, the Yellow Sea Cold Water Mass, the Yellow Sea Warm Current and biological activities.

Particle-size distribution and phosphorus forms as a function of hydrological forcing in the Yellow River.

Samples were collected monthly from January to December in 2010, and daily observations were made during the water-sediment regulation event in June-July 2010. Sequential extractions were applied to determine the forms of P in different particle-size fractions and to assess the potential bioavailability of particulate phosphorus (PP). The results indicated that exchangeable phosphorus, organic phosphorus, authigenic phosphorus, and refractory phosphorus increased with the decreasing of particulate size; conversely, detrital phosphorus decreased with the decreasing of particulate size. The content of bioavailable particulate phosphorus (BAPP) varied greatly in different sizes of particles. In general, the smaller the particle size, the higher the content of bioavailable phosphorus and its proportion in total phosphorous was found in these particles. Hydrological forcing controlled the variability in the major P phases found in the suspended sediments via changes in the sources and the particle grain-size distribution. The variation of particle sizes can be attributed also to different total suspended sediment (TSS) sources. Water-sediment regulation (WSR) mobilized only particulate matter from the riverbed, while during the rainstorm soil erosion and runoff were the main source. The BAPP fluxes associated with the "truly suspended" fraction was approximately 200 times larger than the dissolved inorganic phosphorus (DIP) flux. Thus, the transfer of fine particles to the open sea is most probably accompanied by BAPP release to the DIP and can support greater primary and secondary production.

Seasonal Variation and Sources of Dissolved Nutrients in the Yellow River, China.

The rapid growth of the economy in China has caused dramatic growth in the industrial and agricultural development in the Yellow River (YR) watershed. The hydrology of the YR has changed dramatically due to the climate changes and water management practices, which have resulted in a great variation in the fluxes of riverine nutrients carried by the YR. To study these changes dissolved nutrients in the YR were measured monthly at Lijin station in the downstream region of the YR from 2002 to 2004. This study provides detailed information on the nutrient status for the relevant studies in the lower YR and the Bohai Sea. The YR was enriched in nitrate (average 314 µmol·L(-1)) with a lower concentration of dissolved silicate (average 131 µmol·L(-1)) and relatively low dissolved phosphate (average 0.35 µmol·L(-1)). Nutrient concentrations exhibited substantial seasonal and yearly variations. The annual fluxes of dissolved inorganic nitrogen, phosphate, and silicate in 2004 were 5.3, 2.5, and 4.2 times those in 2002, respectively, primarily due to the increase in river discharge. The relative contributions of nutrient inputs to nitrogen in the YR were: wastewater > fertilizer > atmospheric deposition > soil; while to phosphorus were: wastewater > fertilizer > soil > atmospheric deposition. The ratios of N, P and Si suggest that the YR at Lijin is strongly P-limited with respect to potential phytoplankton growth.

[Distribution of phosphorus in surface sediments from the Yellow River estuary wetland].

Surface sediments were collected from Yellow River estuary wetland. The distribution of phosphorus in sediments was analyzed with modified SEDEX. The results indicated that the contents of TP in surface sediments varied from 12.12 micromol x g(-1) to 25.37 micromol x g(-1), and the mean value was 20.70 micromol x g(-1), in which the Detrital P and Authigenic P were the main forms. Median particle size was closely related with the distribution of phosphors, Exchangeable P, Authigenic P and Organic P mainly consisted of smaller sediment size, while Detrital P mainly consisted of larger sediment size. The distribution of P in sediment was affected by organic matter. Exchangeable P, organic P and refractory P increased with the increasing TOC. The bio-available phosphorus included exchangeable P, iron-bound P,organic P and ranged from 1.15-6.74 micromol x g(-1), with an average of 4.27 micromol x g(-1) for all sediment samples. The contribution of BAP to TP was 6.35% -30.4%.

[Mixing behavior of nutrients in different seasons at Liaohe Estuary].

The distribution and species of nutrients in the Daliaohe Estuary were studied in April, July and November, 2010. Concentrations of nutrients displayed obviously seasonal variability in the Daliaohe Estuary. Highest concentrations of PO4(3-) -P, DOP, DTP and TP were in April, and the lowest were in July. While the highest PP was in November, the lowest was in July. The contents of NO3(-) -N and NO2(-) -N reached the highest point in July, and the lowest was in April; however, the highest NH4(+) -N, DON and PN were in April and the lowest were in November. The main existing form of TN was NH4(+) -N in April, while in July and November NO3(-) -N was the dominant. The behavior of NO3(-) -N,DIN and TN was conservative in various seasons; the behavior of NO2(-) -N, NH4(+) -N and DON was conservative in April and November, while nonconservative in July, which indicated the exist of the extra source in the interior of the estuary. The SiO3(2-) of the Daliaohe Estuary was conservative, with the highest average concentration in November and the lowest in April.

[Forms and distributions of particulate phosphorus in the surface sediments of North Yellow Sea].

Surface sediments were collected from the North Yellow Sea in October 2007. The sediments were analyzed with modified SEDEX to obtain six forms of phosphorus. The results indicate that among the total phosphorus the detrital phosphorus and authigenic phosphorus are the main forms and the content varies from 25.7 to 122.5 microg x g(-1) and from 5.7 to 176.2 microg x g(-1), respectively, which taking up 17.0% -56.9% and 10.2% -49.8% of the total phosphorus. The content of exchangeable phosphorus, extractable organic phosphorus, iron-bound phosphorus and refractory phosphorus ranges from 5.5 to 43.9, from 4.1 to 41.4, from 2.3 to 26.7, from 6.0 to 33.6 microg x g(-1), respectively. Detrital and authigenic phosphorus are the major forms of the total phosphorus, indicating that the natural input is the major source of particle phosphorus in the study area. The content of iron-bound phosphorus is low, indicating that human input is minor in the area; mass fraction of the extractable organic phosphorus and refractory organic phosphorus is low, indicating that there is a low organic content while the main form of the total phosphorus is inorganic in the surface sediments of this area. Bioavailable phosphorus as exchangeable phosphorus, extractable organic phosphorus and iron-bound phosphorus account for 6.7% - 33.2% of the total particle phosphorus, indicating that bioavailability of phosphorus in the surface sediments is low.

[Research advances in the effects of environmental factors on the growth and development of Aurelia spp].

Aurelia spp. is a cosmopolitan coastal species, and also, one dominant species of large jellyfish in the coastal waters of China. In recent years, Aurelia spp. bloom events occur frequently in the world, causing severe damage to marine ecosystems, coastal economy, and society development. Aurelia spp. has a complicated life history comprising a benthic asexually-reproducing polyp generation and a sexually-reproducing medusa generation, and various vegetative reproduction (budding, strobilation, and podocyst production) and sexual reproduction. Surrounding physical and biological factors affect each growth stage of Aurelia spp., especially the juvenile stage of planktonic-benthic life cycle, which has major effect on the population dynamics of Aurelia spp. This paper reviewed the research advances in the effects of environmental factors on Aurelia spp. at its different growth and development stages, and discussed some problems worthy of further study, aimed to provide useful reference for the research of the key factors controlling the jellyfish blooms in coastal waters of China.

[Phosphorus forms of the suspended particulate matter in the Yellow River downstream during water and sediment regulation 2008].

Suspended particulate matter samples were collected from Lijin Station on the Yellow River during the 2008 water and sediment regulation. Using water elutriation method, samples were physically separated according to grain size, and phosphorus forms were detected by the improved SEDEX technology. Results show that authigenic apatite phosphorus and organic phosphorus are the dominant forms of the particulate phosphorus. During water and sediment regulation, concentrations of total particulate phosphorus, loosely adsorbed phosphorus, organic phosphorus and refractory phosphorus are lower than those in other time of the year, while the concentration of detrital fluorapatite phosphorus is higher than that in other time. Grain size is the primary variable in the determination of the content of various particulate phosphorus forms. In fine particles, loosely adsorbed phosphorus, organic phosphorus and refractory phosphorus concentrations are high, while detrital fluorapatite phosphorus concentration is high in coarse particles. About 28.3% of the total particulate phosphorus is in the form of bio-available phosphorus, of which organic phosphorus is the major component. During the water and sediment regulation, the fluxes of sediment, particulate phosphorus and particulate bio-available phosphorus are 6.63 x 10(7) t, 3.42 x 10(4) t, and 8.30 x 10(3) t, which are 83.2%, 78.6%, and 80.2% each of the total fluxes in 2008.