Short-term responses to salinity of an invasive cordgrass

Salinity is one of the main chemical factors in salt marshes. Studies focused on the analysis of salinity tolerance of salt marsh plants are very important, since they may help to relate their physiological tolerances with distribution limits in the field. Spartina densiflora is a South America cordgrass, which has started its invasion of the European coastline from the southwestern Iberian Peninsula. In this work, short-term responses in adult tussocks of S. densiflora from southwestern Spain are studied over a wide range of salinity in a greenhouse experiment. Our results point out that S. densiflora has a high tolerance to salinity, showing high growth and net photosynthesis rates from 0.5 to 20 ppt. S. densiflora showed at the lowest salinity (0.5 ppt) high levels of photoinhibition, compensated by higher levels of energy transmission between photosystems. Adaptative mechanisms, as those described previously, would allow it to live in fresh water environments. At the highest salinity (40 ppt), S. densiflora showed a high stress level, reflected in significant decreases in growth, net photosynthesis rate and photochemical efficiency of Photosystem II. These responses support S. densiflora invasion patterns in European estuaries, with low expansion rates along the coastline and faster colonization of brackish marshes and river banks. This revised version was published online in July 2006 with corrections to the Cover Date.     

东江沉积物重金属分布特征及污染评价

采用ICP-MS对东江河流沉积物中的重金属进行分析,发现东江沉积物中Cu、Zn、Cd、Hg等重金属呈现相同的变化特点,高值区和低值区基本一致.东江流域沉积物的重金属污染物主要是Cu、Zn、Cd、Hg、Pb,其平均含量分别为157.29、213.21、0.98、0.42、50.77mg·kg-1,均高于中国大陆沉积物背景值.地累积指数法和Hakanson潜在生态危害指数法对东江流域沉积物污染程度和生态危害程度的评价结果显示,东江沉积物中地累积指数从大到小的顺序为Cd、Cu、Zn、Hg、Pb;从总的污染程度来看,东江沉积物中各重金属对生态风险影响程度从大到小的顺序为Hg、Cd、Cu、Pb、Zn;从总的生态风险指数上看,整个东江流域除处于上游的河源市段生态风险低外,处于中游的惠州段生态风险为"较高",处于下游的东莞段生态风险为"极高".     

Total concentrations and fractionation of heavy metals in road-deposited sediments collected from different land use zones in a large city (Nanjing), China

Abstract

In order to investigate heavy metal contamination in an urban environment during urbanization and economic development, 35 road-deposited sediment samples were collected from seven different land-use zones (commercial, residential, traffic, scenic park, educational, industrial and peri-urban) in Nanjing, a large city in P.R. China. The ranges of total metal concentrations found were: 28.7–272 mg kg^?1 for Cu; 24.8–268 mg kg^?1 for Ni; 37.3–204 mg kg^?1 for Pb; 140–798 mg kg^?1 for Zn; 0.44–2.19mg kg^?1 for Cd; and 60.6–250 mg kg^?1 for Cr. Metal fractionation was carried out using a modified three-step European Bureau of References (BCR) sequential extraction procedure. Cadmium and Zn were found predominantly associated with the acid extractable fractions; Ni and Cr were dominant in the residual fraction; Pb was predominantly associated with the residual and reducible fractions; Cu was dominant in the oxidizable and residual metal fractions. Based on the sum of the acid-extractable, reducible, and oxidizable fractions, Cd, Zn and Pb are potentially the most toxic metals in the road-deposited sediment in Nanjing. No significant differences, except for Zn, were found in the metal fractionation pattern for Cu, Ni, Pb, Cd, and Cr in different land use zones.     

Nitrogen ligation to the manganese cluster of Photosystem II in the absence of the extrinsic proteins and as a function of pH

Three extrinsic proteins (PsbO, PsbP and PsbQ), with apparent molecular weights of 33, 23 and 17 kDa, bind to the lumenal side of Photosystem II (PS II) and stabilize the manganese, calcium and chloride cofactors of the oxygen evolving complex (OEC). The effect of these proteins on the structure of the tetramanganese cluster, especially their possible involvement in manganese ligation, is investigated in this study by measuring the reported histidine-manganese coupling [Tang et al. (1994) Proc Natl Acad Sci USA 91: 704–708] of PS II membranes depleted of none, two or three of these proteins using ESEEM (electron spin echo envelope modulation) spectroscopy. The results show that neither of the three proteins influence the histidine ligation of manganese. From this, the conserved histidine of the 23 kDa protein can be ruled out as a manganese ligand. Whereas the 33 and 17 kDa proteins lack conserved histidines, the existence of a 33 kDa protein-derived carboxylate ligand has been posited; our results show no evidence for a change of the manganese co-ordination upon removal of this protein. Studies of the pH-dependence of the histidine–manganese coupling show that the histidine ligation is present in PS II centers showing the S₂ multiline EPR signal in the pH-range 4.2–9.5. This revised version was published online in June 2006 with corrections to the Cover Date.     

Heavy metals in the Rosetta estuary of the Nile and the adjoining Mediterranean waters: evidence of removal of dissolved heavy metals from waters as a result of possible binding to suspended matter

The Rosetta estuary was partially separated from the Rosetta branch of the Nile by Edfina Barrage, which controls the Nile discharge into the Mediterranean Sea. The study area covers the Rosetta estuary (lotic environment) and the adjoining seawaters (lentic environment) to investigate the local and seasonal distribution of dissolved and particulate copper and zinc, as well as dissolved cadmium in this estuary and to illustrate its influence on the distribution of these metal forms in the inshore seawaters. Besides, emphasis on the removal of dissolved heavy metals from waters by their adsorption onto suspended matter (SM) was also considered. Contrary to particulate copper (PCu), the vertical values of dissolved copper (DCu) decreased generally with depth. Planktonic scavenging and regeneration processes might determine the vertical profiles of the copper forms. The copper data suggest that the surface sources of DCu exceeded the bottom sources, contrary to the sources of PCu. The markedly high and maximum seasonal averages of DCu in the estuary and inshore seawater in July inspite of the high uptake in summer possibly reflect higher amounts of humic materials. The lowest seasonal average value of DCu in the inshore seawater in January suggests removal of copper in presence of maximum value of SM during highest discharge. The highest regional average of DCu at the estuarine mouth coincided with desorption process during mixing of the fresh and salt waters. The vertical values of dissolved zinc (DZn) and particulate zinc (PZn) showed irregular variations and their high concentrations in the surface of the estuarine and inshore seawater indicate possible land-based sources. The high bottom DZn values, however, resulted from its contribution from the interstitial water of the sediments. The data suggest that the surface sources of DZn exceeded the bottom sources and PZn showed the opposite trend in the open sea area. In the estuary, the maximum seasonal average value of DZn accompanied by the lowest seasonal average of PZn in April inspite of the high uptake in spring suggest that desorption was the dominant process. The minimum regional averages of both zinc forms at the estuarine opening and the highest average of PZn near Edfina Barage are correlated with the amounts of SM, which decreased toward the estuarine mouth. The vertical values of dissolved cadmium (DCd) were much lower in the estuary than the other metals. They showed in both environments irregular variations with depth. The bottom maximum value of DCd can be attributed mainly to contamination from the sediments. There was a distinct seasonal variation of DCd. The minimum seasonal average value of DCd in the estuary in April seems to be caused by its specific binding to living plankton found in abundance. The minimum regional average of DCd value was found at the estuarine mouth. The decrease in Cd concentration due to removal from dissolved state is most pronounced in the early stage of mixing. The correlation coefficients of DCd were positive with salinity and negative with SM, indicating that Cd increased seaward. Statistical correlation between Cd and Zn concludes that the factors affecting their distribution are generally the same.