『Abstract
　In order to observe the spatial phosphorus (P) fractions transformations in sediments in relation to bacterial abundance and enzyme hydrolysing organic P-alkaline phosphatase (APA), samples from 35 stations from eutrophic Sulejow Reservoir were taken in spring after flood and in summer after cyanobacterial bloom breakdown. The results show pronounced fluctuations: decrease of average total P in sediments, despite organic matter delivery after cyanobacterial bloom, in parallel with increase of labile P (8.3％) and Ca-bounded P (16.6％) fractions and decline of organic P fraction (28.5％). Higher alkaline activity in sediments in the spring delivered nutrients to water column and supported cyanobacterial bloom development during the summer. Positive correlation between APA and organic P (r=0.37, p＜0.01, n=70) and negative with labile inorganic P (r=-0.44, p＜0.01, n=70) in sediments proved significant role of the APA in phosphorus transformation in sediments and internal loading in the reservoir. During summer, APA was significantly related to bacterial number (r=0.36, p＜0.01, n=35) and bacterial abundance was correlated to organic matter content (r=0.36, p＜0.01, n=35). Such pattern of temporal variations of P transformation in sediments indicates order of solutions for enhancement of recultivation effects of eutrophic dam reservoirs: (1) reduction of organic matter supply in spring and (2) sediment inactivation during summer.

Keywords: Phosphorus; Sediments; Alkaline phosphatase; Cyanobacterial bloom; Dam reservoir』

1. Introduction
2. Methods
　2.1. Site description
　2.2. Sampling and analysis
3. Results
　3.1. Organic matter content in sediments
　3.2. Total phosphorus
　3.3. Phosphorus fractions
　3.4. Orthophosphate concentration in interstitial water
　3.5. Alkaline phosphatase activity
　3.6. Bacterial abundance
4. Discussion
5. Conclusions
Acknowledgments
References