DISTRIBUTION CHARACTERISTICS OF PHOSPHORUS IN SURFACE SEDIMENTS DURING SEASONS OF ALGAE BLOOMS IN BLOOM-ACCUMULATION AREA IN THE TAIHU LAKE

Moon Bay is located along the northern portion of the Taihu Lake.Because the bay mouth is toward the prevailing southeast wind in summer,Moon Bay has long been a bloom-accumulation area and the water quality is serious.In the past years,we found that this area has frequent occurrence of algal blooms.Hypoxia phenomenon is usually accompanied by such a disaster,leading to a great change of the water environment,such as aggregating on surface sediment and accelerating the release rate of phosphorus.Distribution characteristics of phosphorus in surface sediments could also be changed due to the sedimentation and recovery of alga.We sampled sediment cores with the sediment gravity sampler in different seasons(from January to July)from Moon Bay and distribution characteristics of phosphorus in surface sediments were measured with the standard method.The results suggest that total phosphorus(TP)and inorganic-phosphorus(IP)showed a gradual downward trend throughout the investigation stage,with the average value of 535.53mg/kg and 425.90mg/kg,respectively.Organic-phosphorus(OrgP)decreased first and then increased,and reached the maximum value in July(about 1.4to 1.8times higher than winter),with the average value of 87.72 mg/kg.The inorganic-phosphorus forms mainly composed of Fe-combined phosphorus,Al-combined phosphorus and Ca-combined phosphorus,and all forms reached the maximum value in spring during the monitor seasons.The average value of Fe-combined form,Al-combined form and Ca-combined form was 186.86 mg/kg,129.49mg/kg and 97.48 mg/kg,respectively(accounted for 44.43%,31.18% and 23.18% of inorganic-phosphorus).The seasonal distribution of exchangeable form(Ex-P)was gradually increased from winter to spring and then decreased form spring to summer,with the average value of 4.44mg/kg,implying that the Ex-P content in sediment was released into overlying water during the growing season.According to the correlation analysis,we found that Fe-combined form,the Al-combined form and the organic-phosphorus showed a good correlation with the Ex-P phosphorus.The correlation between inorganic phosphorus and total phosphorus was the most significant,indicating that the total phosphorus in the sediment of the studied area was mainly affected and controlled by the inorganic phosphorus.The variance analysis shows that during the monitor months,the exchangeable phosphorus in April showed a significant difference among January,June and July;the Fe-combined phosphorus in April had a significant difference against June and July,and no significant difference against May;the Al-combined phosphorus showed a significant difference among all months;the Ca-combined phosphorus was not very significant different;the value of total phosphorus,organic phosphorus and inorganic showed a significant difference during monitor months.