光照强度对香溪河水华类型影响的模拟实验

探究光照强度对小球藻生长的影响,为香溪河水华预测提供理论依据。小球藻藻种为香溪河河水中平板分裂后逐步纯化所得。培养箱为40 L的方形塑料箱,四周用遮光布严实包裹。培养液30 L。培养液为用放置24 h后的自来水稀释25倍后的BG-11标准培养基,磷浓度0.285 mg/L,氮浓度9.48 mg/L,p H值7.3~7.8。恒温加热棒控制水温24℃。以平行布置的8根日光灯管作为光源,开关不同数量的日光灯管设定光强梯度,光照梯度为0、800、1 500、2 400、3 200、4 500、6 000 lx。采用电磁式真空泵曝气,曝气比率设置为10%。设置2组平行实验,每个培养箱中加入处理后的藻液10 m L。实验过程为期12d,每天上午8∶00取样,监测指标为光密度、叶绿素a、溶解性总磷、溶解性总氮。结果表明,光照强度在800~1 500 lx时易发生长周期的绿藻水华,绿藻水华转变为蓝藻水华的可能性低;3 200~4 500 lx时易发生短周期的绿藻水华;6 000 lx时发生蓝藻水华的风险很大。香溪河在光照强度小于3 200 lx时不必做蓝藻水华防御措施;光照强度大于4 500 lx时,需提前做适当的蓝藻水华防御措施。

Effect of Light Intensity on Algal Blooms in the Lower Xiangxi River

Chlorella vulgaris is a common single-celled green algae, and accounts for a large portion of green algae blooms. Under the same light conditions, Chlorella vulgaris competes with blue-green algae for nitrogen and phosphorous and, to some degree, inhibits the growth of blue-green algae. Thus, studying the growth characteristic of Chlorella vulgaris can help predict the type of algae bloom most likely to occur. This study investigated the effects of varying light intensity on the growth of Chlorella to provide a theoretical basis for predicting algal blooms in the Xiangxi River near its outlet to Three Gorges Reservoir. Chlorella vulgaris was obtained from the Xiangxi River, incubated in a 40L square plastic container after purification and 10 ml of this solution was added to each incubator. The culture solution was BG-11, diluted 25 times with water to give 0.285 mgP/L, 9.48 mgN/L and pH=7.3-7.8, conditions similar to the lower Xiangxi River. The incubator was maintained at 24oC, covered by a cloth for shade, and fresh nutrient solution was added every 24 hours. A vacuum pump was used for aeration and the aeration rate was 10%. Seven light intensities (0 lx, 800 lx, 1500 lx, 2400 lx, 3200 lx, 4500 lx, 6000 lx) were used and the experiment was run in duplicate. The experiment lasted for 12 days and samples were collected at 8 a.m. each day to determine the optical density (OD), chlorophyll a (Chl), dissolved total phosphorous (DTP) and dissolved total phosphorous (DTN). Results show: A long period green algal bloom tends to develop at a light intensity of 800-1500 lx and the chance of transforming to a blue-green algae bloom is low; a short period green algal bloom tends to occur at a light intensity of 3200-4500 lx and a blue-green algae bloom is likely at 6000 lx. When the light intensity is <3200 lx, there is no need to take measures to control blue-green algae; when the light intensity is >4500 lx, it is necessary to take action to prevent and control cyanobacteria blooms. We also found that Chlorella vulgaris biomass, under high light intensity, is estimated more accurately by measuring chlorophyll a rather than optical density. This experiment was run under specific nutrient conditions and should be used for algal bloom prediction only in water bodies similar to Xiangxi River.