[Spectral Characteristics of Dissolved Organic Matter (DOM) Releases from Soils of Typical Water-Level Fluctuation Zones of Three Gorges Reservoir Areas:Fluorescence Spectra].

As an important sources of dissolved organic matter (DOM) in aquatic system, DOM releases from flooding or submerged soils is a key process in water-level fluctuation zones. In this study, four typical sites in water-level fluctuation zones of Three Gorges Reservoir areas were selected to conduct simulated soil flooding experiments, under ambient (open air) and anoxic conditions. By using fluorescence spectrum technique, the dynamic and geochemical characteristics of DOM releases from flooding soils were investigated. Results showed that the trend or model of DOM releases observed by fluorescence spectrum in all soils from four sampling sites was similar to the observation by UV-Vis spectrum. Fluorescence property of DOM releases showed an important contribution to DOM fluorescence in overlying waters. The rapid releases at initial stage and removal mechanism for later dynamic equilibrium were crucial to explain the dynamic "source-sink" equilibrium in whole flooding period. Effect of inorganic mineral adsorption-desorption on humic-like components (A and C peaks) was significant. Also, impact of microbial utilization on protein-like components (B and T peaks) was confirmative. Additionally, all DOM samples had "autochthonousness plus allochthonousness" property. Except Shibaozhai (SB) site in Zhongxian county, during the whole flooding period, all three other sites didn't show any significant difference between ambient and anoxic conditions. They could be explained by the high heterogeneity of soil property including minerals and organic components. Meanwhile, both the UV-Vis and fluorescence spectra were complementary for each other, and they evidentially showed that the "source-sink" (release and removal) mechanism in DOM releases from submerged soils was the core to decide the dynamics of DOM in overlying waters. Importantly, DOM showed higher aromaticity and humification at the initial release stage when flooding occurred, as well as the greater terrestrial source characteristics, which further helped to explain the environmental fates of pollutants in these environmental sensitive areas. It would also be useful for unveiling the role of DOM in environmental system in future.

[Characteristics of phosphorus forms and the effects of UV light in the confluences water of Qujiang-Jialing River and Fujiang-Jialing River].

The confluences water of Qujiang-Jialing River and Fujiang-Jialing River was investigated in this paper for understanding the characteristics of phosphorus (P) forms and the effects of ultraviolet (UV) irradiation. Through analysis of P speciation, the results showed that the concentration of total P was above the Eutrophication threshold (0.2 mmol x m(-3)) in this study. Meanwhile, total dissolved P (TDP) and dissolved inorganic P (DIP) were the predominant forms of total P (TP) and TDP respectively at all sampling sites, which was independent of confluences. After confluences of Fujiang-Jialing River and Qujiang-Jialing River, the concentration of all forms of P in main stream increased, among which particulate P (PP) showed the greatest increase of up to 129%. Furthermore, water was fractionated by relative molecular weight (M(r)) of composition, and the results showed the predominant forms of dissolved P (DP, < 0.22 µm) was in the soluble high M(r) fraction (0.5 x 10(3)-10 x 10(3)), which was ranged from 47%-61% of DP. After confluences, no significant changes of P contents in different M(r) fraction of water were observed in the main stream (Jialing River). Moreover, UV irradiation experiment was conducted, and it suggested that P in free forms of water (< 0.5 x 10(3)) increased by 10% - 29%, as compared with the decreasing P in the other two M(r) fractions of M(r) 10 x 10(3)-0.22 µm and 0.5 x 10(3)-10 x 10(3). Additionally, in comparison with confluence site samples of Fujiang-Jialing River, the decreasing trend of P in colloid fraction (10 x 10(3)-0.22 µm) was higher in Qujiang-Jialing River. Thus, it confirmatively indicated that UV was an important environmental factor influencing the geochemical fate of P in aquatic system.

[Effects of light irradiation on phosphorous releases from typical submerged soils of water-level fluctuation zones of Three Gorges Reservoirs areas].

For understanding the impact of light irradiation on the phosphorus (P) releases from soil-water interface, two types of typical soils sampled from water-level fluctuation zones of Three Gorges Reservoir areas were selected as research objectives, and simulated light irradiation experiment in lab was conducted for unveiling the underlying mechanisms of P releases from submerged soils in the presence of light irradiation. The results showed that light irradiation could inhibit P releases from submerged soils by a certain degree. Under light condition, total P (TP) concentrations in underlying water of submerged purple soil ranged from 0.018 to 0.033 mg x L(-1), as compared to the range of 0.02-0.057 mg x L(-1) in darkness treatment. Additionally, for gray-brown purple soil, TP was in a range of 0.028-0.045 mg x L(-1) when light irradiated, but in the range of 0.04-0. 084 mg x L(-1) under darkness condition. Meanwhile, changes of iron oxides in soils due to light irradiation were possibly to be the important reason to explain the inhabitation of light irradiation on P releases. Moreover, light irradiation resulted in decreasing saturation degree of iron oxides in soils, which further inhibited the iron reduction and production of amorphous iron, further enhanced the underlying mechanisms of decreasing P releases in presence of light irradiation. Further, CO2 and CH4 could reflect decomposition of soil organic carbon (SOC) in submerged condition. Light irradiation significantly decreased SOC transformation into carbon gases. Stimulating consumption of inorganic electron acceptors in submerged soils could also be used to explain the changes of iron oxides under light irradiation condition. Thus, inhabitation of light irradiation on P releases from submerged soils obviously related with iron minerals reduction and decomposition of organic matter in soils.

[Seasonal variation characteristics of phosphorus speciation in the sediment of Changshou Lake].

To further know the seasonal variation characteristics of phosphorus species in lake sediment, the contents of different phosphorus species in the surface sediment sampling from Changshou Lake were determined by using the SMT sequential extraction method in July and November, 2009, and March, 2010. The contents of total phosphorus (TP) basically show an order of the low-water period, high-water period, and normal-water period from high to low, and the maximum appeared in Shoudao (2960.29 mg/kg) while the minimum in Guanjiakou (586.05 mg/kg). The mass fractions of phosphorus associated with hydrous ferric/aluminum oxides (Fe/Al-P) and organic phosphorus (OP) in TP at all sampling sits are in an order of the normal-water period, high-water period, and low-water period from high to low, and the maximum of Fe/Al-P appeared in Lewen (40.01%) while that of OP in the dam mouth (72.44%). The mass fraction of phosphorus bound to calcium salt (Ca-P) in TP is in an order of the low-water period, normal-water period, and high-water period, and the maximum appeared in Baibudang (15.52%). These results suggested that the phosphorus speciation in the sediment of Changshou Lake shows obviously temporal and spatial distribution characteristics, and Fe/Al-P is mainly influenced by pH of the overlying water, while OP is not apparently influenced by dissolved oxygen (DO).