[Concentration of Phosphorus in Sediments Interstitial Water as Affected by Distribution of Aquatic Plants in Dianchi Lake].

In order to reveal the effect of aquatic plants distribution on the mass concentration of phosphorus in sediment interstitial water, the mass concentrations of Dissolved Total Phosphorus (DTP), Soluble Reactive Phosphorus (SRP) and Dissolved Organic Phosphorus (DOP) in the sediment interstitial water and overlying water from areas with or without plants in the same site of Dianchi were studied. The vertical variation characteristics of phosphorus forms in sediment interstitial water were analyzed to explore the effect of aquatic plants on the phosphorus forms in sediment interstitial water. The results showed: ①Aquatic plants had an significant effect on the phosphorus mass concentration of the sediment interstitial water in different Dianchi lakes. However, they varied with different distribution sites and depth. ②Aquatic plants significantly decreased the percentage of DOP contribution in the sediment interstitial water. The average contribution of DOP with aquatic plants was 32.87%, while that without plants reached 57.68%; ③Aquatic plants significantly inhibited the release of inorganic phosphorus in sediments and promoted the transformation of DOP. The SRP diffusion flux at sediment-water interface with aquatic plants was increased by 39.99% as compared with that without plants; ④The growth of aquatic plants significantly reduced the concentration of phosphorus in sediment interstitial water, especially DOP, and the reduction rate of the sediment interstitial water DOP was from 38.02% to 85.49%. Therefore, the analysis of the contribution and reduction rate of aquatic plants on the sediment interstitial water DOP was of great importance in understanding the relationship between aquatic plants and DOP, as well as the mineralization of organic phosphorus in sediments.

Effects of organic matter and submerged macrophytes on variations of alkaline phosphatase activity and phosphorus fractions in lake sediment.

Organic matter and submerged plants may affect internal phosphate loading in lake sediment. In this study, we investigated the changes of alkaline phosphatase activity (APA) and phosphorus (P) fractions in lake sediment by adding organic matter (0.0%, 0.5% and 1.0% of dry weight) and plant submerged plants under experimental conditions. Results indicated that the APA in sediments significant increased after 50 days incubation than at 7 days. The APA in the treatments by adding organic matter and submerged plants increased by 26.37%-61.78% than that of control after 7 days incubation, and increased by 1.00%-29.51% at 50 days, indicating both organic matter and submerged plants may remarkable affect APA in sediment, especially for the early stage of incubation. In addition, the soluble reactive P (SRP) concentrations of the overlying water increased significantly with increasing sediment organic matter, possibly related to increase of APA in sediment. However, the release of SRP was obvious restrained due to absorption of submerged plant. TP and P fraction in sediment decreased with increasing incubation time, but the decrease of TP content in sediment was mainly from NaOH-P and OP sources, but not from HCl-P and IP. Effects of organic matter and submerged plants on P fractions in sediment mainly occurred in NaOH-P and OP fractions. At the end of experiments, the contents of NaOH-P and OP in the treatments by adding organic matter and submerged plant decreased by 5.46%-20.47% and 7.87%-21.46%, respectively. These results indicated that the relative importance of organic matter and submerged plants during the release and transformation of P in lake sediment.

[Relationship between the DO and the environmental factors of the water body in Lake Erhai].

The contents of DO and nitrogen (N), phosphorus (P), chlorophyll a in water from Lake Erhai were analysed by combining the nitrogen and phosphorus forms in sediment. The results indicated that the DO contents of the water from Lake Erhai varied from 6.61 to 7.42 mg/L from 1992 to 2009, which is generally decreased. The minimum mean value was 6.42 mg/L in September. The trend of the DO contents from north to south was decreasing, and also decreased with the increasing of the water depth in Lake Erhai, the DO content was 5.15 mg/L at the water bottom. The relationship between the contents of DO and N, P was negative, and the relativity of different months was greater than that of different years. The relationship between the contents of DO and the contents of labile-P, organic-P, NH4(+) -N in sediment was negative, which was positive with the contents of Fe/Al-P, inorganic P and NO3(-) -N. The relationship between the contents of DO and chlorophyll a in water was negative, which indicated that Lake Erhai is aerobic, and is approaching anaerobic gradually. With the increasing of released content of N and P, the increasing of alga biomass was accelerated and the worsening of water body eutrophication also can be promoted by the decreased DO content in water from Lake Erhai.