Abstract
To clarify the effects of nutrient addition on algal growth during the early stages of phytoplankton bloom, an microcosm experiment was conducted in early spring; it included two groups of in situ samples: sediment plus lake water (S+W), representing the nominal “control”, and sediment plus 50% BG11 medium and 50% lake water (S+BW), representing the treatment of nutrient addition. The results demonstrated the recruitment biomass of non-cyanobacteria in the treatment group was about 46.7% of that in the control group, and the recruitment biomass of cyanobacteria in the treatment group was approximately 5 times than that in the control. After recruitment, nutrient addition generated remarkable stimulation of the growth of all algae, especially cyanobacteria. The results suggested that the stimulation by nutrient addition of algal growth after recruitment may be responsible for the occurrence of phytoplankton blooms, and the more pronounced promotion of cyanobacteria than non-cyanobacteria was explainable for the strengthening of the dominance of cyanobacteria during eutrophication.
Highlights
Eutrophication is becoming a serious environmental problem in freshwater ecosystems
Previous studies mainly focused on the relationship between nutrient levels and the occurrence of a phytoplankton bloom (Paerl et al, 2011), and few were involved in the effect of nutrient addition on algal growth during the early stages
The results from the present study demonstrated that nutrient addition increased the recruitment biomass of cyanobacteria and concurrently stimulated the subsequent growth of both cyanobacteria and non-cyanobacteria
Summary
Eutrophication is becoming a serious environmental problem in freshwater ecosystems. Excessive nutrients in water leaded to frequent occurrence of cyanobacteria bloom, which threatened the safety of water environment (Smith et al, 1999). The seasonal cycling of algae is divided into different stages based on their growth characteristics (Reynolds et al, 1981). Kong and Gao (2005) proposed “the theory of four stages” for the formation of phytoplankton blooms, in which algal recruitment is followed by massive growth and propagation of algae prior to the occurrence of a phytoplankton bloom. The effect of nutrient increase on algal growth during the early stages was vital in revealing the features of summer blooms. Previous studies mainly focused on the relationship between nutrient levels and the occurrence of a phytoplankton bloom (Paerl et al, 2011), and few were involved in the effect of nutrient addition on algal growth during the early stages
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