Effects of Cyanobacterial Growth and Decay on Nitrogen Transformation in Lake Taihu
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摘要: 氮是控制蓝藻生长和水华形成的关键元素之一，反之蓝藻水华也会对氮的浓度变化和形态转化产生影响. 通过采集太湖竺山湾蓝藻、沉积物和水样，设立湖水对照组(A0)、湖水加藻避光培养处理组(A1)、泥柱避光培养处理组(A2)、泥柱加藻避光培养处理组(A3)、湖水加藻光照培养处理组(A4)、泥柱加藻光照培养处理组(A5)进行室内培养试验，探究在蓝藻生长和衰亡的不同时期中氮的转化过程. 结果表明：①蓝藻生长会大量吸收水体中的溶解态氮，最终A4和A5处理组中DTN浓度分别降低46.4%和60.7%、NO3−-N浓度分别降低61.7%和80.6%. ②蓝藻的衰亡会降低水体DO浓度，加速底泥氮素脱除，试验结束时A0和A1处理组中NO3−-N浓度基本无变化，A2和A3处理组中NO3−-N浓度分别降低40.8%和56.6%. ③蓝藻衰亡时会释放大量NH4+-N，大幅提高水体中DTN浓度，并因试验期间的低溶氧条件使得NH4+-N无法转换成硝酸盐，抑制氮素的脱除，试验结束时DTN浓度分别升高77.6%和59.2%. 研究显示，蓝藻的生长可以通过吸收水体中的NO3−-N来降低反硝化作用的底物浓度，从而会在短期内降低反硝化脱氮效率；而蓝藻水华的衰亡则会促进沉积物的反硝化脱氮作用，但当NO3−-N被完全脱除后，水华降解导致的低DO浓度会阻碍硝化作用的发生，短期内打破耦合硝化-反硝化的脱氮过程. 对于浅水湖泊而言，频繁的风浪扰动作用，会使水体处于厌氧-耗氧交替过程，强化耦合硝化-反硝化过程. 因此，尽管蓝藻水华的大量生长会与反硝化竞争NO3−-N，短期内抑制湖泊脱氮过程，但从蓝藻生长-衰亡的整个生命周期来看，蓝藻水华的发生则会促进湖泊氮素的脱除.Abstract: Nitrogen is one of the key elements controlling the growth and bloom formation of cyanobacteria. Conversely, cyanobacterial bloom also affects nitrogen concentration variation and form transformation. By collecting cyanobacteria, sediment and water samples from Zhushan Bay of Lake Taihu, indoor incubation experiments were set up as lake water only (A0), lake water with algae in light-proof culture (A1), sediment column without algae in light-proof culture (A2), sediment column with algae in light light-proof culture (A3), lake water with algae in light culture (A4) and sediment column with algae in light culture (A5) to investigate the process of nitrogen transformation during different periods of cyanobacterial growth and decay. The results showed that: (1) The growth of cyanobacteria would uptake a large amount of dissolved nitrogen in the water column, and finally the DTN concentration decreased by 46.4% and NO3−-N concentration decreased by 61.7% in A4, and the DTN concentration decreased by 60.7% and NO3−-N concentration decreased by 80.6% in A5. (2) The decay of cyanobacteria induced decrease of DO concentration and accelerated the nitrogen removal from the sediment. At the end of the experiment, there was basically no change in the NO3−-N concentration in the A0 and A1, and the NO3−-N concentration in the A2 and A3 was reduced by 40.8% and 56.6%, respectively. (3) The decay of cyanobacteria increased the DTN concentration in the form of NH4+-N. Nitrogen removal was inhibited due to the inability to convert NH4+-N to NO3−-N as a result of low dissolved oxygen conditions during the experiments. This study inditates that the growth process of cyanobacteria reduces the substrate concentration for denitrification through the uptake of NO3−-N in the water column, which may reduce the denitrification efficiency in the short term; In contrast, the decay of cyanobacterial blooms promotes denitrification in sediments, but the resulting low DO concentrations can impede nitrification, breaking the coupled nitrification-denitrification process in the short term. For shallow lakes, frequent wind and wave disturbances can put the water column in an anaerobic-oxygen depletion alternation process, which can strengthen the coupled nitrification-denitrification process. Therefore, although the growth of cyanobacterial blooms competes with denitrification for NO3−-N and inhibit lake denitrification processes in the short term, cyanobacterial blooms may enhance nitrogen removal efficiency of lake from the perspective of the entire life cycle of cyanobacterial growth-decay.
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Key words:
- Lake Taihu /
- cyanobacterial blooms /
- nitrogen /
- denitrification /
- transformation
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图 3 各组DTN浓度随时间的变化
Figure 3. The change of the DTN concentration in each group with time
图 4 各组NO3−-N浓度随时间的变化
Figure 4. The change of the NO3−-N concentration in each group with time
图 5 各组NO2−-N浓度随时间的变化
Figure 5. The change of the NO2−-N concentration in each group with time
图 6 各组NH4+-N浓度随时间的变化
Figure 6. The change of the NH4+-N concentration in each group with time
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