Determinant variables on the isotopic values of particulate organic matter in a neotropical floodplain

Particulate organic matter(POM)is an important energy source for aquatic consumers,understanding its origin and composition is essential for understanding the energetic dynamics of aquatic environments.The aim of this study was to analyze the relationship between POM and phytoplankton(isotopic values and chlorophyll concentration)and abiotic variables during dry and rainy seasons.Sampling was conducted in rivers and lagoons in the floodplain of the Upper ParanáRiver.We found a greater difference in ^(δ13)C values of POM between sampling points than between seasons,indicating that the composition of regional sources influences the composition of POM more than dry and rainy seasons.In addition,the concentration of chlorophyll during the dry season was positively correlated with ^(δ13)C values during that rainy period.Additionally,we found a relationship between factors limiting the growth of phytoplankton and ^(δ13)C values of POM,such as phosphate ions,indicating that variables that regulate phytoplankton growth tend to influence the composition of POM in river floodplains.Therefore,maintaining the variables that regulate the phytoplankton community is of fundamental importance for the composition of POM,an important energy source in aquatic environments.

Distribution and Assessment of Soil and Land Degradation in Subtropical China—A Case Study of the Dongxi River Basin, Fujian Province *1

Some alternative methods for estimating soil erosion rates rapidly were used to elucidate the relationship between the land use types and land degradation. The 137 Cs content, magnetic susceptibility, aggregate stability, and soil properties were studied in the Dongxi River Basin, a mountainous area of western Fujian. A plot of 137 Cs inventory (Y) against slope angle (X) shows a strong inverse log log relationship ( r = -0.83 ), indicating that much more soil erosion occurs on steeper slopes. Average soil loss (in thickness of top soil per year) in the past 30 years for arable slope crest, arable slopes and tea plantation slopes are 1.6 , 10.4 and 8.0 mm year -1 respectively. The surface layer enrichment factor of magnetic susceptibility (Y) in soil also shows an inverse log log relationship ( r =-0.63), indicating a similar tendency with the relationship between the 137 Cs inventory (Y) against slope angle (X). The physical and chemical properties of soils among different land use types show different degraded characteristics at different significant levels.

Corrosion behavior and corrosion products of a low-alloy weathering steel in Qingdao and Wanning

A newly developed low-alloy weathering steel has been exposed in two coastal sites （Qingdao in the north, Wanning in the south） in China for one year. The samples in Wanning corroded far more seriously than those in Qingdao. The rust layer formed on the steel was analyzed by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, N2 adsorption approach, polarization curves, and electrochemical impedance spectroscopy （EIS）. The rust formed in Qingdao contains more X-ray amorphous compounds and is more compact than that formed in Wanning. Cr and Cu are enriched in the rust layer near the steel matrix, and the phenomenon is more obvious in Qingdao than in Wanning. The rust layer formed in Qingdao suppresses the anodic and cathodic reaction more remarkably than that formed in Wanning does. The rust layer formed in Qingdao possesses a higher ability to block the permeation of chloride ions than that formed in Wanning does.

CORROSION BEHAVIORS OF THE EXPOSED SIDE AND UNDERSIDE OF LOW ALLOY WEATHERING STEEL IN QINGDAO AND WANNING FOR 18 MONTHS

For 18 months, a newly developed low alloy weathering steel has been exposed in two coastal sites （Qingdao in the north China, Wanning in the south China）. The different corrosion behaviors of the exposed side and the underside of the samples were characterized by X-ray diffraetion （XRD）, polarization curve, electrochemical impedance spectroscopy （EIS）, scanning electron microscopy （SEM）, and N2 adsorption approach. It was found that the samples exhibited higher corrosion rate in Wanning than that in Qingdao. The underside of the samples corrodes more seriously than the exposed side in Qingdao, whereas the result in Wanning is just the reverse. The protection performance of rust layers mainly depends on its compactness and the enrichment of Cu and Cr is a secondary causation. The different compactness of rust layers in the exposed side and the underside originates from different corrosion conditions of the two sides.