Phosphorus forms in sediments of the East China Sea and its environmental significance

By means of SEDEX, ASPILA and XRF, depth-dependent changes of different phosphorus forms in sediment cores from specific areas of the offshore Changjiang Estuary (Yangtze Estuary) in 1998 were analyzed. Results show that contents of total phosphorus (TP), organic-phosphorus (OP) and iron-phosphorus (Fe-P) decreased down-core, while those of absorbed-phosphorus (Ad-P) and calcium-phosphorus (Ca-P) increased. The distribution tendency of detritus-phosphorus (De-P) is not obvious. Results also show that TP, Fe-P and OP contents at Meso station of the Changjiang Estuary and Hangzhou Bay are higher than that of the other stations. This suggests that the pollutants carried by the Changjiang and the Qiantang rivers from inland have affected the natural environment in offshore area. TP, Fe-P and OP contents of each station become higher from bottom to top, indicating the amount of the terrestrial pollutants carried by the two rivers has been enhanced since the last 30-50 years. Ad-P, Ca-P, Fe-P and OP are all active phosphorus in sediments, and their re-cycling in sediment is closely related to each other.

Plotting the Clarifying Curves and Determination of the Specific Amount of Settled Material during the Initial Period to Sedimentation in Stationary Column of Aqueous Suspensions of Solids

The present paper presents an algorithm and a program for plotting the clarifying curves and for determination of the specific amount of settled material during the initial period based on data obtained from sedimentation experiments in stationary column of aqueous suspensions of solids particles with different concentrations. The algorithm and program have been developed for an interactive, rapid and convenient processing of the data obtained from sedimentation experiments in stationary column of aqueous suspensions of solids particles and allow obtaining with accuracy of precise and expressive graphs which characterize the behaviour of aqueous suspensions to sedimentation in stationary column. Sedimentation study of different aqueous suspensions of solids particles in stationary column is of great importance for experimentally determining the important parameters required to design and exploitation clarifiers and sludge thickeners from waste water treatment plants.

Growth characteristics of algae during early stages of phytoplankton bloom in Lake Taihu,China

Three treatments, sediment plus lake water （S＋W）, sterilized sediment plus lake water （SS＋W）, and sediment plus filtered lake water （S＋FW）, were recruited to investigate the growth characteristics of algae during pre-bloom and the importance of algal inocula in the water column and sediment. The results showed that in the water column, biomass of all algae increased in all treatments when recruitment was initiated, whereas this tendency differed among treatments with further increment of temperature. The process of algal growth consisted of two stages： Stage I, the onset of recruitment and Stage II, the subsequent growth of algae. Compared with S＋W, in Stage I, SS＋W significantly increased the biomass of cyanophytes by 178.70%, and decreased the biomass of non-cyanophytes by 43.40%; In Stage II, SS＋W notably stimulated the growth of all algae, thus incurring the occurrence of phytoplankton bloom. Further analyses revealed that both metabolic activity and photochemical activity of algae were enhanced in SS＋W, which resulted from the releasing of nutrients from sediment. These results suggest that algal growth in Stage II and algal inocula in the water column can be important factors for the formation of phytoplankton bloom. In addition, possible mechanisms promoting algal recruitment and subsequent growth of algae were explored.