三峡水库春季营养盐和浮游植物空间分布及其影响机制

为研究三峡水库春季水体营养盐与浮游植物的空间分布状况,于2013年3月对三峡水库22条支流及干流的6个断面进行采样监测. 结果表明:来水、回水、河口和干流4类断面ρ(TN)平均值分别为1.69、1.84、2.01、1.51 mg/L；ρ(TP)平均值分别为0.115、0.191、0.179和0.181 mg/L；不同类型断面间ρ(TN)、ρ(TP)差异不显著；水体中N、P的主要形态分别为NO₃--N和PO₄3--P；N/P〔n(N)/n(P)〕从来水(110.8)至干流(18.9)逐渐降低. 三峡水库总体上为中营养状态,回水和河口区富营养化程度较高,富营养断面比例分别为45.4%和36.4%. 研究期间共检出浮游植物8门98属,其中以绿藻门、硅藻门和蓝藻门为主,分别检出42、26和17属；从组成上看,来水和干流断面以硅藻-绿藻为主,回水、河口断面以绿藻-硅藻为主. 浮游植物丰度由高到低依次为回水、河口、来水和干流断面. 调查期间,22条支流中有15条支流在不同位置发生水华,但主要集中在回水区；拟多甲藻水华为主要类型且集中在库区的下游支流,而库区中上游支流则以隐藻、衣藻、小球藻、小环藻等水华为主. 环境因子排序分析表明,在水华集中的回水-河口区域,影响浮游植物丰度分布的主要环境因子数明显少于其他区域,温度和ρ(DO)为该区域浮游植物丰度分布的主要影响因子,而ρ(TN)、ρ(TP)的影响不明显. 

Spatial Distribution of Nutrients and Phytoplankton and Causes for Their Differences in Three Gorges Reservoir in Spring

A survey of 22 tributaries and 6 mainstream sections of the Three Gorges Reservoir (TGR) was conducted in March 2013 to study the spatial distribution of nutrients and phytoplankton composition in four categories of sections. The results showed that the total nitrogen concentrations in each kind of section-incoming flow, backwater, estuary and mainstream-were 1.69,1.84,2.01 and 1.51 mg/L, respectively. The total phosphorus concentrations in each kind of section were 0.115,0.191,0.179 and 0.181 mg/L, respectively. No significant differences (determined by using single factor ANOVA) were observed on TN (P=0.659) and TP (P=0.683) concentrations among the incoming flow, backwater, estuary and mainstream sections. Nitrate and dissolved phosphate were the dominant forms of TN and TP, suggesting that nutrient limitation was not an important regulator of algal growth. The N∶P ratio declined along the direction of water flow from the incoming flow (110.8) of the tributaries to the mainstream of the Yangtze River (18.9). On the whole, the study area was mesotrophic, while the backwater and estuary sections had higher trophic levels, with 45.4% and 36.4% eutrophic sections, respectively. In total, 98 genera of phytoplankton were identified, dominated by Chlorophyta, Cayanophyta and Bacillariophyta, with 43,6 and 17 genera, respectively. With regards to phytoplankton composition, the incoming flow and the mainstream sections were dominated by Bacillariophytes followed by Chlorophytes, whereas the backwater and estuary sections were dominated by Chlorophyta followed by Bacillariophyta. The phytoplankton abundance was highest in the backwater section and declined along the estuary, incoming flow and mainstream sections. Algal blooms were observed in 15 out of 22 tributaries, and most of them occurred in the backwater section. The most frequent blooms were dominated by Peridiniopsis sp., which was observed in the backwaters of 7 of the 8 closest tributaries to the Three Gorges Dam. In contrast, the dominant bloom forming species in the middle and upstream tributaries of TGR were more diverse, with the dominant blooming species Cryptomonas sp., Chlamydomonas sp., Chlorella sp. and Cyclotella sp. Ordination Analysis determined that the number of main environmental factors affecting the distribution of phytoplankton abundance in the backwater-estuary region was obviously less than in the other regions. The temperature and dissolved oxygen (DO) were the first two key factors determining the distribution of algae abundance within the region. TN and TP were not main factors affecting the phytoplankton abundance.