Spatial characteristics of nitrogen forms in a large degenerating lake: Its relationship with dissolved organic matter and microbial community

Sediments have a significant influence on the cycling of nutrient elements in lake environments. In order to assess the distribution characteristics and estimate the bioavailability of phosphorus and nitrogen in Dianchi Lake, organic and inorganic phosphorus and nitrogen forms were analysed. The 210Pb radiometric dating method was employed to study temporal changes in the phosphorus and nitrogen pools in Dianchi Lake. The result show that the total phosphorus (TP) and total nitrogen (TN) were both at high concentrations, ranging from 697.5–3210.0 mg/kg and 1263.7–7155.2 mg/kg, respectively. Inorganic phosphorus (IP) and total organic nitrogen (TON) were the main constituents, at percentages of 59%–78% and 74%–95%, respectively, in the sediments. Spatially, there was a decreasing trend in phosphorus and nitrogen contents from the south and north to the lake centre, which is related to the distribution pattern of local economic production. The burial rates of the various phosphorus and nitrogen forms increased in same spatially and over time. Particularly in the past two decades, the burial rates doubled, with that TN reached to 1.287 mg/(cm2·yr) in 2014. As the most reactive forms, nitrate nitrogen (NO3-N) and ammonia nitrogen (NH4-N) were buried more rapidly in the south region, implying that the potential for releasing sedimentary nitrogen increased from north to south. Based on their concentrations and burial rates, the internal loads of phosphorus and nitrogen were analysed for the last century. A TP pool of 71 597.6 t and a TN pool of 81 191.7 t were estimated for Dianchi Lake. Bioavailable phosphorus and nitrogen pools were also estimated at 44 468.0 t and 5429.7 t, respectively, for the last century.

Internal Loads and Bioavailability of Phosphorus and Nitrogen in Dianchi Lake, China

Application of geochemical techniques for prospecting unconventional phosphate sources: A case study of the lake sediments in Eppawala area Sri Lanka

Suspended solids are an important part of lake ecosystems, and their nitrogen and phosphorus contents have a significant effect on water quality. However, information on nitrogen and phosphorus forms in suspended solids remains limited. Therefore, a case study was conducted in Lihu Lake (China), a lake with characteristically high amounts of suspended solids. Nitrogen and phosphorus speciation in suspended solids was analyzed through a sequential extraction method. We also evaluated the sources of various forms of nitrogen and phosphorus and their different effects on eutrophication. The total nitrogen (TN) content was 758.9–3098.1 mg/kg. Moreover, the proportions of various N forms in the suspended solids of the study areas were ranked as follows: Hydrolyzable nitrogen (HN) > residual nitrogen (RN) > exchangeable nitrogen (EN). Total phosphorus (TP) ranged from 294.8 to 1066.4 mg/kg, and 58.6% of this TP was inorganic phosphorus (IP). In turn, calcium (Ca)-bound inorganic phosphorus (Ca-Pi) was the main component of IP. The correlation between various nitrogen and phosphorus forms showed that there were different sources of suspended nitrogen and phosphorus throughout Lihu Lake. Correlation analysis of water quality indices and comparative analysis with surface sediments showed that in Lihu Lake, the dissolved nitrogen and phosphorus contents in water were influenced by sediment through diffusion, while particle phosphorus content in water was influenced by suspended solids through adsorption; however, due to the higher phosphorus contents in suspended solids, we should pay more attention to the impact of suspended solids.

Forms of Nitrogen and Phosphorus in Suspended Solids: A Case Study of Lihu Lake, China

Nutrients accumulation in drainage channel sediments

Changes in carbon and nitrogen with particle size in bottom sediments in the Dan River, China

A calorimetry system has been developed in Experimental Advanced Superconducting Tokamak (EAST). It is employed to evaluate the heat load exhausted by cooling water. Full poloidal coverage is achieved after the upgrade in 2019. The experimental results show that the heat load exhausted by cooling water is 64%–86% of the injected energy. Moreover, the heat load increases faster in the case with a higher heating power, and this is qualitatively confirmed by the simulation. In addition, a longer time is required for the temperature of the cooling water to achieve its maximum for a higher heating power. And in the decay phase of the water temperature, it shows an exponential characteristic. The averaged time constant of the thermal decay obtained by exponential fitting for the upper and the lower divertor are 12.1 s and 107.9 s, respectively. It indicates that the heat removal capability of the upper tungsten divertor outperforms the lower graphite divertor.

Calorimetry system for heat load in long-pulse discharges on EAST tokamak

Investigation of key factors for ITB formation and maintenance in EAST high β discharges

The paper investigates the effect of pedestal turbulence, i.e. coherent mode (CM), on the divertor total particle flux, the particle flux distribution and heat flux distribution, and their decay lengths in the scrape-off layer (SOL) region on EAST tokamak. The experimental evidence indicates the coherence between the pedestal CM and the divertor particle flux fluctuation, which implies that the pedestal CM can affect the divertor plasma behavior. The increase of the particle flux decay length (λjs) correlates with the density radial decay length (λ n,SOL) in the SOL region where the λ n,SOL is largely affected by the change of pedestal CM amplitude. A quantitative statistical analysis shows that the divertor total particle flux and λjs in the SOL region increase with increasing amplitude of the electron density fluctuation and the electron temperature fluctuation induced by the pedestal CM. The temporal decay process of the total particle flux is interrupted by the appearance of CM at the pedestal. Meanwhile, the spatial distributions of the divertor particle flux and heat flux are enhanced when the pedestal CM appears, which are observed in both the upper single null and lower single null configurations.

Impact of coherent mode on divertor particle and heat flux in a type I ELMy H mode plasma on EAST tokamak

Investigation of Key Factors for Itb Formation and Maintenance in East High [[Equation]] Discharges

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