Phosphorus Fractions Transformation in Sediments Before and After Cyanobacterial Bloom: Implications for Reduction of Eutrophication Symptoms in Dam Reservoir

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.