Phosphorus Fractions In River Sediments And Experimental Study On Phosphorus Release

Sediment cores from Haihe River mainstream, surface sediments and riparian soil from Alafia River stream were collected. Spatial distributions of total phosphorus contents and phosphorus fractions in these sediments were determined experimentally. Correlations between phosphorus fractions and sediment characteristics, distributions of microbial biomass phosphorus with different land use patterns and the effect of multiple factors (dissolved oxygen, organic carbon, aluminum) on phosphorus release from sediments were discussed. Furthermore, outdoor column experiments were carried out to study static release of phosphorus, nitrogen and COD from sediments. The main results were as follows:1. Sediments in the Mainstream of Haihe River were mainly comprised of fine sand and very fine sand, accounting for 30.9%-54.7% and 28.8%-63.7%, respectively. Clay and coarse sand contents were quite low. Total contents of organic matter and total phosphorus in the sediments of Haihe River mainstream were in the range of 4.07%-8.43% and 560-1035mg/kg, which were similar to those in Taihu Lake. Sediment pollution in Haihe River mainstram was at higher level compared to other river sediments in China. Vertical profiles of total phosphorus contents was decreased with increasing depth, and the highest vaule was found in surface sediments. The calcium bound phosphorus (HCl-P) is the largest sediment phosphorus fraction, accounted for 60～80% of sedimentary TP. This reflected that over half amount of the phosphorus was not bioavailable in Haihe River mainstream. Exchange phosphorus (NH4Cl-P) content was quite low in the sediments. Except carbon bound phosphorus, other phosphorus fractions were correlated well with contents of fine grain sedimts (r> 0.72).2. Coarse sand was the dominated component in the Alafia River stream sediments. Generally speaking, the order of P-fractions in most sediment samples was ranked as H2SO4-P> NaOH-P> CDB-P> NH4Cl-P. P fractions were related to pollution status and physiochemic characteristics of sediments. Organic matter and microbial biomass phosphorus contents in riparian soil of Alafia River watershed was diffferent. The microbial biomass phosphorus ranged from 86.4 to 479.6mg/kg. The rank order of microbial biomass phosphorus contents with different land use patterns was Forest> Agricultural land> Residents> Mining.3. It was indicated in the study that the anaerobic condition was much more propitious to the P transformation at the water-sediment interface than the aerobic condition. It also showed that aluminum was able to retain phosphorus in sediments. Addition of OC reduced the release of phosphorus from sediments to overlying water without addition of Al under aerobic and anaerobic conditions. However, with addition of Al under both anaerobic and aerobic conditions the OC enhanced the release of phosphorus from sediments to overlying water.4. It was showed in the study that the dredging depth had an effect on the release of nitrogen and phosphorus from sediments to overlying water. The concentrations of total nitrogen, total phosphorus, and COD in the overlying water of column experiments decreased from bottom to top vertically. Dredging and replacement of overlying water with tap water could decrease the concentrations of total nitrogen, total phosphorus, while sediment could sustainded release nitrogen and phosphorus. The concentration of nitrogen and phosphorus will meet the needs of eutrophication.