滨岸带水华堆积与消散特征及其营养盐效应

Characteristics and effects on nutrients of algal blooms accumulation and dissipation in littoral zone

为了解滨岸带植被、地形等地貌要素对蓝藻水华堆积及消散过程的影响,在太湖滨岸带设置不同形式的围格和植被实验区,通过逐日监测水体叶绿素a(Chl-a)的消长过程及同步营养盐变化,研究夏季蓝藻水华在湖泊滨岸带堆积与消散特征和营养盐效应.结果表明,滨岸带的地形地貌及植被状况对蓝藻水华的堆积程度及消散过程影响较大,软围隔营造的滨岸带静水环境,以及不同植被所形成的不同滞水区,显著加剧了蓝藻水华的局部堆积,从岸边挺水和浮叶植被区到开敞水域对照区,蓝藻水华的堆积程度依次递减;近岸挺水和浮叶植被区蓝藻水华堆积最严重,堆积时间最早,持续时间长;蓝藻水华堆积对营养盐等水质指标影响极大,堆积严重时该区域Chl-a含量达到了457.42μg/L,总氮(TN)达到11.04mg/L,总磷(TP)达到1.32mg/L;橡胶围格内浮叶植物区藻类堆积程度与近岸区类似,而浮叶植物与沉水植物混合区藻类堆积程度低于单一浮叶植物区;水体围隔能够加剧蓝藻水华的堆积,没有围隔的浮叶植物区藻类堆积程度最低.在蓝藻水华堆积过程中,蓝藻细胞仍在继续增殖,水体Chl-a仍会明显增加,而同期的水体营养盐的增幅小于Chl-a,甚至随着藻类生长消耗及生态系统的脱氮效应,溶解态氮磷下降明显.蓝藻水华消散过程中,TN、TP与Chl-a同步下降,但藻体中的氮磷释放到水中,导致堆积区的溶解态氮、磷有所增加,显示出明显的营养盐效应.本研究定量刻画了蓝藻水华局部堆积并快速致灾的地形地貌要素特点,揭示了蓝藻水华的水质与生态效应,为科学评估富营养化水体蓝藻水华的生态灾害风险提供科学依据.

The accumulation, dissipation and oxygen consumption of algal blooms would result in ecological disaster in the littoral zone. In order to discuss the effects of the vegetation and topography on the accumulation and dissipation of cyanobacteria bloom, different forms of enclosure, together with aquatic plants were constructed in the coastal zone of Lake Taihu, we observed the fluctuation of Chlorophyll-a（Chl-a） and the synchronous change of nutrients. Results showed that stagnant environment was conducive for algae proliferation and accumulation, where built soft enclosure, and aquatic plants could promote algae accumulation. Algal bloom was the most earliest and serious in the emerged and floating-leaved aquatic plants restoration area. Chl-a raised to 457.42μg/L, the content of total nitrogen（TN） and total phosphorus（TP） increased to 11.04 mg/L and 1.32 mg/L, and it was second serious in the enclosure, where restorated floating-leaved aquatic plants. Algal bloom was less accumulating in the floating-leaved and submerged macrophytes area. There was insignificant difference in the fishing net zone and control point. During the process of algal blooms, cyanobacteria continued to proliferate, then Chl-a raised more than TN and TP, and with the growth of algae and the denitrification effect of ecosystem, dissolved nitrogen and phosphorus decreased. When algal bloom dissipated, nutrients released into water, and dissolved nutrients raised most in the rubber enclosure. This study showed the risk characteristic of algal bloom in lakes. And the result will help to prevent the bloom risk and produce the control policy.