title: The low TN:TP ratio, a cause or a result of Microcystis blooms?
abstract: An enclosure experiment in the shallow, subtropical Lake Donghu, China, was performed in the summer of 2001 to examine the effect of TN:TP (total phosphorus) ratios and P-reduction on the occurrence of Microcysitis blooms. The treatments were performed with enough amounts of N but with different amounts of P in the water column and sediment. Microcystis blooms occurred in the enclosures either with an initial TN:TP <29 or TN:TP>29 where the nutrients (N, P) were high enough. Microcysitis blooms never occurred in the treatments with low P concentration in spite of the presence of sufficient N. The P-rich sediments served as an important source for the P supply in the water column, and such a process was activated greatly by the outburst of Microcystis blooms which pumped up selectively P from the sediments and thus decreased the TN:TP ratios. Therefore, the low TN:TP ratio is not a cause but rather a result of Microcystis blooms.
authors.affiliation: Donghu Experimental Station of Lake Ecosystems, State Key Laboratory for Freshwater Ecology and Biotechnology of China, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, China.
authors.forename: Liqiang
authors.initials: L
authors.lastname: Xie
authors.forename: Ping
authors.initials: P
authors.lastname: Xie
authors.forename: Sixin
authors.initials: S
authors.lastname: Li
authors.forename: Huijuan
authors.initials: H
authors.lastname: Tang
authors.forename: Hong
authors.initials: H
authors.lastname: Liu
mesh_terms: D005068:Eutrophication; D019015:Geologic Sediments; D046931:Microcystis; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D010758:Phosphorus / Q000032:analysis / Q000378:metabolism*; D014881:Water Supply
chemical_list: D010758:Phosphorus; D009584:Nitrogen