[Effects of Exogenous Inputs on Phosphorus Recovery and Transport in Newborn Surface Layers from Sediment Dredging].

The effect of external pollution inputs on phosphorus recovery, transport, and transformation in newborn surface layers from sediment dredging remains unclear. Clarifying this issue is important for the control and management of external pollution loads at the watershed scale, particularly after the implementation of sediment dredging activities. In this study, sediments in Meiliang Bay of Lake Taihu were investigated. In-situ dredging simulation was used to study the transport and transformation of phosphorus at the sediment-water interface, before and after dredging, with either external or non-external particulate matter inputs, and to explore the effect of dredging on phosphorus release as part of internal loading. The results showed that limiting the inputs of external particulate matter and dredging had positive impacts on the control of TP and TN in the sediments. Dredging significantly reduced the content of potentially mobile phosphorus (Mobile-P) in surface sediments. Iron-bound phosphorus (Fe-P) was the first main component of the reduced Mobile-P and Organic phosphorus (Org-P) was the second. The content of Loose-bound phosphorus (Lb-P) was less than 1‰ of the total phosphorus. After 210 days of the experiment, the concentration of PO43--P in the pore water of the dredged treatment was lower than that of the undredged treatment, and this difference was more pronounced without external particulate matter input. Furthermore, the concentration of PO43--P in the pore water of the dredged treatment (without external particulate matter input) was maintained at a low level, while this first increased and then subsequently decreased for the other treatments. The concentrations of PO43--P in pore water were positively correlated with Fe-P in the corresponding sediment layers. Source-sink transition took place between winter and spring, leading to the switch in sediment functioning as a sink to a source. The results indicated that dredging could reduce the release rate of internal phosphorus from sediments. Furthermore, limiting the input of external particulate matter plays an important role in facilitating the control of internal phosphorus loading by dredging.

[Distribution Characteristics and Fluxes of Nitrogen and Phosphorus at the Sediment-water Interface of Yuqiao Reservoir].

Yuqiao Reservoir is an important source of drinking water in Tianjin. In recent years, the eutrophication status is becoming more and more serious, but its internal loading and distribution characteristics of nitrogen and phosphorus is not clear. The profiles of nitrogen and phosphorus at the sediment-water interface were analyzed using the Peeper (pore water equilibrium) technique and the spatial distribution was investigated. The existing forms of the released nitrogen and phosphorus were investigated by the static intact sediment cores, and the fluxes of nitrogen and phosphorus at the sediment-water interface were estimated by static incubations with intact sediment cores. The results demonstrated the following. ① The contents of PO43--P, NH4+-N, NO3--N, and NO2--N in sediments were 0.5-6.5, 0.5-10.9, 2.2-16.2, and 0.05-0.6 mg ·kg-1, respectively. The contents of nutrient were lower as depth increased, and horizontal distribution characteristics indicated significant differences. ② The contents of PO43--P and NH4+-N in the interstitial water were much higher than in the overlying water, suggesting that the interstitial water had the potential to diffuse nutrients to the overlying water. The concentrations of PO43--P and NH4+-N in the interstitial water increased rapidly at 0-5 cm and then decreased gradually. ③ PO43--P and NH4+-N diffused from the sediment to the overlying water, and the fluxes of them were 1.1-13.3 mg ·(m2 ·d)-1 and 20.6-250.5 mg ·(m2 ·d)-1, respectively. The exchange fluxes of NO3--N and NO2--N ranged from -20.4 to 33.4 mg ·(m2 ·d)-1 and from -7.4 to 0.4 mg ·(m2 ·d)-1, respectively. PO43--P and NH4+-N were the main nutrients in the sediment released to the overlying water. The fluxes were high in the south and low in the north, and also high in the mouth of the Linhe River and downstream of the reservoir. Compared with similar studies, the fluxes at the sediment-water interface of Yuqiao Reservoir were relatively high, indicating that the sediment was an important source of nutrients for the overlying water in Yuqiao Reservoir.

[Characteristics of N2O Release and Influencing Factors in Grass-type and Algae-type Zones of Taihu Lake During Summer].

Spatial heterogeneity of N2O generation and emissions in multi-ecotype lakes limited the accurate estimation of the N2O fluxes in lakes, but few studies on the characteristics of N2O generation and emissions have been conducted. In this study, N2O flux at the water-gas interface, dissolved N2O concentration in the water column, and N2O flux at the sediment-water interface in typical grass-type and algal-type zones of Taihu Lake were analyzed during summer, and indoor micro-environment experiments were conducted to illustrate the main factors affecting the generation and emissions of N2O. The results showed that the N2O fluxes at the water-gas interface, dissolved N2O concentration, and N2O fluxes at the sediment-water interface of the emergent macrophyte type area was higher than the algae-type area and submerged macrophyte area during the summer., with N2O fluxes at the water-gas interface of (115.807±7.583), (79.768±1.842), and (3.685±0.295) µmol ·(m2 ·h)-1, respectively. The dissolved N2O concentration in the water column were (0.051±0), (0.029±0.001), and (0.018±0) µmol ·L-1, respectively; and the N2O fluxes at the sediment-water interface were (178.275±3.666), (160.685±0.642), and (75.665±1.016) µmol ·(m2 ·h)-1, respectively. The spatial difference could be attributed to dominant plants and the concentration of inorganic nitrogen in the water column. The results of micro-environment experiments showed that nitrate and organic carbon sources could significantly increase the N2O production potential of sediments, the high concentration of NH4+-N in the water column might inhibit the N2O production in sediments, and the production rates of N2O in the sediment increased remarkably when the incubation temperature increased, suggesting that the generation and emissions of N2O were mainly restricted by nitrate, organic carbon, and temperature in summer.

A new study on diffusion tensor imaging of the whole visual pathway fiber bundle and clinical application.

BACKGROUND: With conventional imaging methods only the morphous of the visual nerve fiber bundles can be demonstrated, while the earlier period functional changes can not be demonstrated. We hypothesized that diffusion tensor imaging (DTI) would demonstrated the whole optic never fiber bundle and visual pathway and the earlier period functional changes. The purpose of the present study was to evaluate the application of DTI technique in the demonstration of the whole optic never fiber bundle and visual pathway, and the influence of orbital tumors on them. METHODS: GE 1.5 T signa HD MR System, and the software package DTV2 were adopted. The total 45 subjects were enrolled, including 15 volunteers and 30 patients. All patients had ocular proptosis from minor to major. Seven patients had visual acuity decrescence. RESULTS: The nerve fiber bundles, e.g. optic chiasma, optic tract and optic radiation in posterior visual pathway were well demonstrated in all cases. Wherein, the intact whole visual pathway fiber bundles were clearly revealed in 10 volunteers and 17 patients, and optic nerve was not wholly revealed in the rest of the subjects. Shift of optic nerve caused by compression and partial deformation were seen in 7 patients with orbital tumor. In 6 of 7 patients, DTI displayed significant abscise and deformation of visual nerve. Chi-square test indicated significant correlation between visual acuity decrescence and DTI visual nerve non-display. CONCLUSIONS: Visual nerve fiber bundles and the whole visual pathway were visualized in most of patients with DTI. It might be an effective method of providing imaging evidence for visual nerve fiber earlier period functional changes, and laid a foundation for the study in other cranial nerves.