The decomposition of macrozoobenthos induces large releases of phosphorus from sediments.

Lake eutrophication and algal blooms may result in the mortality of macrozoobenthos. However, it is still not clear how macrozoobenthos decomposition affect phosphorus (P) mobility in sediments. High-resolution dialysis (HR-Peeper) and the diffusive gradients in thin films (DGT) technique were used in this study to assess the dissolved organic matter (DOM), dissolved/DGT-labile iron (Fe), P, and sulfur (S(-II)) profiles at a millimeter resolution. The decomposition of Bellamya aeruginosa significantly increased the internal loading of sediments P. The Fe(III) and sulfate were reduced under anaerobic conditions and promoted P desorption from sediments. This was supported by the significant increase in DGT-labile S(-II) and dissolved/DGT-labile P, Fe(II) and the significant positive correlation between Fe and P on day 8. The simultaneous increase in DOM and soluble reactive phosphorus (SRP) and the significant positive relationship between these factors were observed during the decomposition of B. aeruginosa. This suggested that complexation of DOM with metals may promotes the release of P from sediments.

Phosphorus mobilization in lake sediments: Experimental evidence of strong control by iron and negligible influences of manganese redox reactions.

Iron (Fe) and manganese (Mn) reactions have been regarded as the primary factors responsible for the mobilization of phosphorus (P) in lake sediments, although their individual roles are hard to distinguish. In this study, in situ mobilization of P, Fe and Mn in sediments was assessed by high resolution spatio-temporal sampling of their labile forms using diffusive gradient in thin films (DGT) and suction device (Rhizon) techniques. It was found that the monthly concentration distributions showed greater agreement and better correlation coefficients between labile P and labile Fe, than those between labile P and labile Mn, implying that Fe plays a key role in controlling P release in sediments. Furthermore, better correlations were observed between hourly changes in concentrations of soluble reactive phosphorus (SRP) and soluble Fe(II), than those between SRP and soluble Mn. Changes were observed under simulated anaerobic incubation conditions, suggesting that P release was caused by the reductive dissolution of Fe oxides. This was supported by the lack of influences on P release from reductive dissolution of Mn oxides in the sediment-water interface and top sediment layers under the anaerobic incubations. In simulated algal bloom experiments, positive correlations and consistent changes were observed between SRP and soluble Fe(II) concentrations, but not between SRP and soluble Mn concentrations. This further demonstrated the Fe-dependent and Mn-independent release of P in sediments. Therefore, Fe redox reactions have a high impact on P mobilization in sediments, while Mn redox reactions appear to have negligible influences.

Long-term effectiveness of sediment dredging on controlling the contamination of arsenic, selenium, and antimony.

This study assessed the effectiveness of dredging in controlling arsenic (As), selenium (Se), and antimony (Sb) contamination in sediments, by examining contaminant concentrations in sediments six years after dredging was completed. High-resolution diffusive gradients in thin films (DGT) and dialysis (HR-Peeper) techniques were used to monitor the concentrations of DGT-labile metalloids and soluble metalloids in sediments, respectively. Results revealed that dredging effectively remediated metalloid contamination in sediments only in April, July and/or January. Compared to non-dredged sediments, the concentrations of soluble and DGT-labile As, Se, and Sb in dredged sediments decreased on average by 42%, 52%, and 43% (soluble), and 54%, 50%, and 53% (DGT), respectively. The effectiveness of the dredging was primarily due to the transformation of metalloids from labile to inert fractions, which increased the ability of the sediments to retain the metalloids, and the slowed rate of resupplied metalloids from available solid pools. In contrast, negligible/negative effects of dredging were seen in October, and the concentrations of soluble and DGT-labile metalloids even increased in some profiles of dredged sediments. This was mainly caused by a release of the metalloids from algal degradation, which may offset the dredging effectiveness.

Chemical constituents of flowers and fruits of Rabdosia excisa.

AIM: To study the chemical constituents in the flowers and fruits of Rabdosia excisa. METHODS: The compounds were isolated and purified by silica gel column chromatography and their structures were identified by spectroscopic methods. RESULTS: Sixteen compounds isolated from the flowers and fruits of this plant were identified as: stigm asterol (I), α-amyrin palmitate (II), ursolic acid (III), 2α, 3α, 19-trihydroxy-urs-12-en-28-oic acid (IV), 2α-hydroxyursolic acid (V), maslinic acid (VI), isodonal (VII), maoyecrystal E (VIII), kamebakaurin (XI), macrocalyxin G (X), epinodosinol (XI), rabdosichuanin C (XII), kamebacetal A (XIII), oridonin (XIV), enmenol-glucoside (XV), and lasiononin (XVI). CONCLUSION: All the constituents were found in Rabdosia excisa for the first time, except constituents III, IX, XII and XIV.

[Chemical constituents about the stem of Rabdosia excisa].

OBJECTIVE: To investigate the constituents of the stem of Rabdosia excisa. METHOD: Compounds were separated and purified by silica gel column chromatography and their structures were determined by spectroscopic method. RESULT: Thirteen compounds isolated from this plant were identified as rabdesimte( 1 ), maoyecrystal E (2), 6beta,11alpha,15alpha-trihydroxy-6,7-seco-6,20-epoxy-1alpha, 7-ol-ide-ent-kaur-16-en (3), enmenol-glucoside (4), oridonol (5), macrocalyxin G (6), rabdosichuanin C (7), beta-sitosterol (8), ursolic acid (9), 2alpha-hydroxyursolic acid (10), maslinic acid ( 11 ), 2alpha,3alpha,19-trihydroxy-urs-12-en-28-oicacid (12), and daucosterol (13). CONCLUSION: Except for compounds 5, 8, 9 and 13, the remaining compounds were found in R. excisa for the first time.