Rethinking terrestrial dissolved organic matter in dam reservoirs before mixing: Linking photodegradation and biodegradation and the phenanthrene binding behavior.

With the increased construction of dam reservoirs and the demand for water security, terrestrial dissolved organic matter (DOM) has received attention because of its role in regulating water quality, ecological functions, and the fate and transport of pollutants in dam reservoirs. This study investigated the transformations of soil DOM and vegetation DOM of dam reservoirs following photodegradation and biodegradation before conservative mixing, as well as the resultant effects on phenanthrene binding. Based on the results, terrestrial DOM could undergo transformation via photodegradation and biodegradation before conservative mixing in dam reservoirs. Although both processes resulted in substantial decreases in DOM concentrations, the changes in chromophoric DOM and fluorescent DOM depended on the original DOM sources. Furthermore, the photodegradation of terrestrial DOM resulted in more pronounced photobleaching than photomineralization. In addition, photodegradation of terrestrial DOM resulted in the generation of DOM-derived by-products with low molecular weight and low aromaticity, whereas the biodegradation of terrestrial DOM resulted in DOM-derived by-products with low molecular weight and high aromaticity. Subsequently, the photodegradation and biodegradation of terrestrial DOM substantially enhanced the binding affinity of phenanthrene. Soil DOM is prior to vegetation DOM when predicting the ecological risk of HOCs. These results indicate that the terrestrial DOM in dam reservoirs should be reconsidered before conservative mixing. Further studies on the coupling effects of both biogeochemical processes, as well as on the relative contributions of soil DOM and vegetation DOM after transformation to the aquatic DOM in dam reservoirs, are required. This study provides information on the environmental effects of dam construction from the perspective of biogeochemical processes.

Effects of human management on black carbon sorption/desorption during a water transfer project: Recognizing impacts and identifying mitigation possibilities.

Water resources management is an important public concern. In this study, we examined the extent of sorption/desorption of trace pollutants to soil black carbon (BC) in the water level fluctuation zone (WLFZ) of the middle route of the South to North Water Transfer Project in China. In addition, we investigated the main management measures affecting these processes during the project. The results showed that the pseudo second-order model adequately describes the sorption/desorption of phenanthrene on the soil BC in the WLFZ. Water level fluctuation may indirectly influenced BC sorption/desorption by altering water chemistry. Water level residence time had negative effects on BC sorption in short-term experiments (days to months), but the impact gradually diminished with increased residence time. The results suggested that long-term field monitoring of water chemistry is urgent. During the initial period of water transfer, delaying the water supplies as drinking water source or directly irrigating crops could mitigate the adverse impacts. Future research should focus on the water-soluble products of BC degradation. The findings of this study should be useful in improving sustainable management of water resources for water transfer projects.

Ultrastructural studies on the natural leaf senescence of Cinnamomum camphora.

The process of natural leaf senescence of Cinnamomum camphora (C. camphora)-a commercial tree in Asia, was investigated, focusing on changes in cellular ultrastructure, epicuticular wax, and stoma. The changes to mesophyll cells in a senescing leaf predominantly include degradation of the following cellular components: cytoplasm, the central vacuole, small vacuoles, and vesicles with a diameter smaller than 400 nm, which are involved in the degradation of chloroplasts. The sequence of change in epicuticular wax during leaf senescence was different from those in herbaceous plants by atomic force microscope and scanning electron microscopic analysis. Comparing with maturation leaves, senescing leaves develop a wider aperture in their stoma, which would delay the leaf senescence of C. camphora.

[Landscape change during rapid urbanization in Shenzhen].

By using the satellite images of 4 periods of time, including the data from Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), Multi Spectral Scanner (MSS) and SPOT this paper analyzed the landscape change in Shenzhen Special Economic Zone of Guangdong Province, South China in 1979-2003, aimed to study the temporal-spatial landscape change characteristics, their causes, and major driving forces in this zone. The results revealed that the characteristic of landscape change were completely different among test three periods (1979-1990, 1990-2000 and 2000-2003). During the first period (1979-1990), urbanization developed very rapidly, and the natural vegetations mainly in Futian, Luohu and Yantian districts degraded and transformed into a landscape with anthropogenic components. In the second period (1990-2000), landscape conversion mainly took place in Nanshan and Futian districts, where various types of landscape were transformed into impervious surfaces, and parts of the vegetations were transformed into anthropogenic landscapes. During this period, typical urban characteristics were formed, whereas the remaining vegetations, especially forest stand, were little disturbed. In the third period (2000-2003), subtle consolidation was observed, and the use of pervious material in certain areas counteracted the adverse ecological impacts of urbanization. The extent of urbanization still increased, but the intensity of landscape change was at lower level than that in previous periods.