太湖原位围隔中水深对苦草生长的影响

2015年6月15日至7月27日,在太湖北部湖湾原位围隔中,通过盆栽试验方法,利用不锈钢架,采用湖泥培养的苦草(Vallisneria natans),进行为期45 d的原位试验。试验共设置3个水深梯度,分别为1.0 m、1.5 m和2.0 m,依次记为D_1、D_2、D_3;将试验架顶部固定在围隔的浮体上,通过上下浮动保持试验水深,观测苦草在不同水深梯度下生长指标的变化,分析水深对苦草生长的影响,探究苦草在太湖北部湖湾生长的适宜水深。结果表明,不同水深围隔间的总氮、总磷浓度和蓝藻数量不存在显著差异(P0.05)。水深是影响苦草生长的关键因子,不同水深梯度下苦草的成活率、分蘖数和平均叶长等指标均存在一定差异。苦草的成活率随水深增加明显降低,1.0 m水深苦草的成活率与其他2组差异显著(P0.05),试验第7天,3个水深处理组苦草的成活率分别为91%、30%和27%;第28天,3组成活率依次降至64%、9%和5%。试验前期,苦草的平均叶片长度随水深增加而减小,试验后期D_1组苦草叶片出现断裂现象,试验第14~28天,D_1组苦草平均叶长由10.3 cm缩短到4.46 cm,缩减了57%。1.0 m水深苦草有分蘖出现,1.5 m和2.0 m均未出现分蘖现象。1.0 m以内湖滨带较适合太湖北部湖湾苦草的恢复重建,但需借助消浪桩和软围隔等措施降低风浪和蓝藻水华对沉水植物生长的影响。

In Situ Enclosure Study on Growth of Vallisneria natans at Different Water Depths in Taihu Lake

Eutrophication is a serious threat to water supply safety and ecological security. Eco-restoration, such as planting submerged macrophytes, can control eutrophication effectively and water depth is an important factor affecting the growth and distribution of submerged macrophytes. Thus, studying the effect of water depth on the growth of submerged macrophytes would benefit efforts to control eutrophication. The main purpose of this study was to investigate the growth response of Vallisneria natans (V. natans) to different water depth in an enclosure study. From June 15 to July 27, 2015, a pot experiment was conducted in the northern area of Taihu Lake. Pots were held in stainless steel frames suspended from floats at different depths (D1=1.0 m, D2=1.5 m and D3=2.0 m). During the 45 day experiment, samples were collected once a week for measurement of total nitrogen, total phosphorus, cyanobacteria density, and growth parameters of V. natans. No significant differences were observed in TN, TP or cyanobacteria among the three groups (P>0.05) and water depth was the key factor affecting growth of V. natans. Survival rate, tiller number and average blade length varied by group. Survival rate of V. natans decreased with increasing water depth and the survival rate at D1 was significantly higher than at D2 and D3 (P<0.05). From day 7 to the day 28, the survival rates at D1, D2 and D3 decreased, respectively, from 91% to 64%, 30% to 9% and 27% to 5%. In the early stage of the experiment, the average blade length of V. natans decreased with increasing depth, and blade breakage occurred in group D1 near the end of the experiment. From day 14 to day 28, average length of the leaves in D1 decreased from 10.3cm to 4.46 cm, a 57% reduction and tillering was only observed in group D1. Our study indicates that the restoration of V. natans is best carried out at water depths of less than 1.0 m and it is necessary to reduce the influence of wind, waves and cyanobacteria blooms on the growth of submerged macrophytes using wave attenuations and soft enclosures.