[Chemical Oxygen Demand(COD) Composition and Contribution in Typical Waters of Baiyangdian Lake].

Chemical oxygen demand (COD) is an important index used to assess organic oxygen consumption pollution. To explore COD composition in the natural water in Baiyangdian Lake, the main composition, source, and influencing factors of oxygen-consuming organic substances in the water body were revealed through physical continuous classification, three-dimensional fluorescence, and other methods. The results showed that the COD of the two waters was affected by dissolved organic substances (protein-like and humus-like organic matters) with size of less than 220 nm (59%-93%), and inorganic substances had little effect on COD. The source of organic matter in overlying water was primarily affected by endophytic vegetation decomposition, sediment release (the release flux of TOC was in the range of 1.55-2.28 mg·(m2·d)-1), and other endogenous sources (biological index>0.8), as well as by land-based sources such as reed platform and artificial pollution (1.4

[Spatial distribution character of phosphorus fractions in surface sediment from Chaohu Lake].

Phosphorus fractions, organic matter and particle size of the surface sediment from Chaohu Lake were analyzed for spatial distribution and the risk of phosphorus release. The result showed that total phosphorus (TP) of surface sediment was 790 mg x kg(-1), which was 55% higher than that in 1980s, with 386 mg x kg(-1) higher in western lake and 211 mg x kg(-1) higher in eastern lake. NaOH-Pi of sediment ranged from 55 to 648 mg x kg(-1), and occupied average 25% of TP. NaOH-Po of sediment ranged from 27 to 468 mg x kg(-1), and occupied average 17% of TP. NaOH-Pi and NaOH-Po in western lake were 331 mg x kg(-1) and 225 mg x kg(-1), which were significantly higher than those in eastern lake. Ca-P and Res-P accounted for 18% and 40% of TP, and were equably distributed in the lake. TP, NaOH-Pi and NaOH-Po of sediment in the western lake increased intensively with the depth, while Ca-P and Res-P showed no significant change in the vertical profile in the lake. Profile of phosphorus fractions showed that NaOH-Pi and NaOH-Po were the dominant factions of the increasing phosphorus sedimentation in the western lake. Phosphorus of sediment in the western lake will release more easily to the water with higher organic matter and higher content of sandy silt.

[Effect of iron plaque on root surfaces on phosphorus uptake of two wetland plants].

In situ micro-suction cups were used to collect samples of soil solution with Arundo donax Linn and Typha latifolia from defined segments at rhizosphere in field. The experiment was conducted to elucidate the contribution of iron plaque while wetland plants were used to remove phosphorus. The reddish iron plaque was observed and measured on the surfaces of roots of Arundo donax Linn and Typha latifolia in the field, 20,170.8 mg/kg (fresh weight) for Arundo donax Linn and 7640.3 mg/kg (fresh weight) for Typha latifolia were collected. Olsen-P contents of Arundo donax Linn with iron plaque were 28.85 mg/kg, 46.2% more than that of without, 34.99 mg/kg for Typha latifolia 21.9% more than that of without. The phosphate concentrations in the in situ rhizosphere soil solution of Arundo donax Linn with iron plaque were 0.65 mg/kg, 9.2% more than that of without, 0.56 mg/kg for Typha latifolia, 33.9% more than that of without. The phosphorus contents adsorbed by iron plaque were 81.7% for Arundo donax Linn and 85.7% for Typha latifolia of the wetland plants with iron plaque. Phosphate use efficiency of Arundo donax Linn with iron plaque was 16.5% more than that of without, 31.4% for Typha latifolia. The contents of phosphorus of single plant of the two wetland plants with iron plaque are higher than that of without. Due to adsorb phosphate with iron plaque, the transfer speeds of phosphate from non-rhizosphere to rhizosphere and from soil to soil solution are increasing. The phosphorus contents with iron plaque accumulated at rhizosphere and depleted at rhizosphere without iron plaque of Arundo donax Linn and Typha latifolia.

[In situ dynamics of phosphorus in the rhizosphere solution and organic acids exudation of two aquatic plants].

A mini-rhizotron experiment with Alternanthera philoxeroides and Typha latifolia was conducted to measure the spatial and temporal dynamics of phosphorus in the rhizosphere solution. The organic acids in the in situ rhizosphere soil solution were analyzed. A decreasing phosphorus concentration gradient in soil solution toward the root was observed for both A. philoxeroides and T. latifolia. The phosphorus concentration in the rhizosphere soil solution of A. philoxeroides (2.53 mg x L(-1)) was lower than that of T. latifolia (5.43 mg x L(-1)) in the forth sampling day. Compared to T. latifolia, A. philoxeroides released more malic acid (27.33 umol x L(-1)) which was more efficient in phosphorus mobilization. A. philoxeroides was more effective in phosphorus uptake in the rhizosphere than T. latifolia.

[Phosphorus rhizosphere depletion effect of four aquatic plants].

Four aquatic plants (Alternanthera philoxeroides, Typha latifolia, Sagittaria sagittifolia, Phragmites communis ) were cultured on P-enriched soil in a pot experiment to assess the phosphorus rhizosphere depletion effect and analysis the ratio of root to shoot, root morphology, phosphorus uptake efficiency and phosphorus use efficiency. An obvious variation in P concentration of the soil in the rhizophere and non- rhizophere was observed. Compared with the non-rhizosphere (available P: 167.53 microg x g(-1)), the available P in the rhizosphere soil of Alternanthera philoxeroides, Typha latifolia, Sagittaria sagittifolia and Phragmites communis was reduced to 80.17, 124.37, 155.38 and 161.75 microg x g(-1) respectively, with 81%, 42%, 18% and 16% reduction ratio of water-soluble phosphorus. More effective phosphorus depletion was achieved in Alternanthera philoxeroides by higher phosphorus uptake efficiency (1.32 mg x m(-1)), while rooting system was small and phosphorus use efficiency was low (0.34 g x mg(-1)). Phosphorus uptake efficiency of Typha latjfolia is much lower (0.52 mg x m(-1)) than that of Alternanthera philoxeroides, however, its strong rooting system enhanced soil exploration, with higher phosphorus use efficiency (0.64 g x mg(-1)) and the ratio of root to shoot (0.35). Alternantshera philoxeroides and Typha latfolia were more effective in phosphorus depletion of the rhizosphere soil than that in Sagittaria sagittifolia and Phragmites communis.