| Black bloom, which creates a deteriorative environment in aquatic systems, generally occurs in shallow aquatic systems such as lakes, rivers, and seashores in the summer months. The water is highly hypoxic on the occurrence of black bloom and abruptly becomes black and malodorous. The blackness spreads quickly over a large hypoxic zone within a few days, leading to the death of fish and other aquatic organisms. Since the last century, black bloom has occurred in many lakes worldwide. Recently, black bloom has become a serious social and environmental problem. Taihu Lake, located in Eastern China, is the third largest freshwater lake in China, and is seriously affected by human economic activities. Taihu Lake also is typical shallow lakes and algal Lake. It is of great significance that identifies the causation and critical controlling factor of black bloom, and forms a perfect system to prevent, forecast, inhibition and solve black bloom.In the paper, the algae, the sediment and the water for testing were collected from Moon Bay of Taihu Lake where black bloom has occurred frequently in recent years.. Based on the survey of the condition of Taihu Lake, the formation of black bloom was simulated which was induced many possible influencing factors to find the key contributor to black bloom and explore the measure to prevent or forecast the formation of black bloom. The results were as follows:1. The five strains were isolated and screened from the sediment. SRB118 was chose as the test strain for short growth cycle and higher blackness. The SRB118 was identified as Desulfovibrio.2. SRB was the main biological factor of black bloom. The surface SRB population density increased with time in formation of black bloom, which has a good linear relative in formation of black bloom with Fe2+ concentration, H2S concentration and blackness. The SRB promoted to the formation of H2S and FeS-the main component of the black substance in the black bloom. The iron is rich fresh lake sediment, but lake sediment lacks sulfur and marine sediments are rich in it. So that the Fe2+ concentration were higher than H2S concentration in formation of black bloom and sulfur reduction was the limiting factor of the FeS formation. The H2S and blackness has a good linear relative in formation of black bloom. And the abrupt increase in H2S concentration signaled the impending black bloom occurrence.3. The s large amounts of corruption algae was the material base of the black bloom. The sediment with the corruption of massive algae promoted SRB (Sulfate-reducing bacteria) proliferation. The algae corruption also caused the DO (Dissolved oxygen)、Eh (Oxidation-reduction potential) and pH dropped to lmg/L,-7.5 mV and 6.83 on 10th day, respectively. The temperature was higher in the deeper water than the surface water. In the hot season, the black bloom was susceptible to bursting once the algae corrupted with short time (2-6 days) under the effect of SRB. The uplift force of volatile substances and the higher temperature of the deeper water versus the surface water resulting from the algal corruption accelerated the material exchange and caused the organic algal debris and the nascent black metal sulfide to float upward.4. The possibility evaluation of the organic matter resulting from corruption algae inducing black bloom was, protein>starch>cellulose. The minimum protein recruitment inducing black bloom was 5 g in 1 kg surface sediment, which can induce black bloom after 2 days, and the Fe2+, H2S and blackness increased with protein recruitment increasing. The most likely recruitment of starch and cellulose inducing black bloom was 25 g/kg and 15 g/kg separately, which induced black bloom after 8 days. The blackness of black bloom induced by starch and cellulose was lower than protein.5. Heavy metal pollution was very serious in sediment of Taihu Lake, and heavy metals content was Hg<Pb<Cu<Fe. The Hg2+ recruitment was very low in sediment (0-0.1 mmol/kg), but Hg2+ advanced black bloom bursting 2 days. Hg2+promoted growth of H2S while had inhibition of increasing of Fe2+ and blackness. The lower Pb2+、Cu2+ and Fe3+ recruitment in sediment (<0.5 mmol/kg) promoted growth of H2S while the higher recruitment (>0.5 mmol/kg) inhibited. The Pb2+、Cu2+ and Fe3+ is the inhibitor of increasing of Fe2+ and blackness, and the inhibition increased with recruitment. The lower Pb2+、Cu2+ and Fe3+ recruitment t (<0.5 mmol/kg) can induce black bloom. The amorphous ferric oxide promoted growth of H2S even higher recruitment (10-200 mmol/kg) and had inhibition of Fe2+ and blackness. The lower amorphous ferric oxide recruitment(10 mmol/kg) can induce black bloom and advance black bloom bursting, while the higher recruitment deferred black bloom bursting.6. The recruitment of SRB and algae induce black bloom, advance black bloom bursting and strengthen the blackness. So it is effective measures that inhibit promoted SRB proliferation or accumulation of algae to prevent black bloom. Dredge is one of main measures to govern eutrophic lake. In summer with higher temperature, if there was mass accumulation of algae, the black bloom could burst in the area dredged a month but the area dredged 3-7 months. In the area where had dredged more than 7 months, the sediment system gradually recovers from dredge and turns to situation which is prone to bursting black bloom. As a result, dredge should be carry out in autumn and winter to avoid accumulation of algae and short dredge period that black bloom is prone to bursting. |
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