不同营养水平湖泊浮游植物吸收和比吸收系数变化特征

摘要

Phytoplankton absorption and chlorophyll-specific absorption coefficients were analyzed,and the causes were discussed by selecting four different trophic level lakes including Lake Taihu,Lake Tianmu and Lake Bositeng.According to trophic level index using chlorophyll-a(Chl.a),total nitrogen,total phosphorus and secchi disc,Lake Taihu includes hyper and medium eutrophication zones.Meanwhile,Lake Tianmu and Lake Bositeng are light eutrophic and mesotrophic,respectively.Phytoplankton absorption coefficients at 440 nm (aph (440)) are 1.02 ± 0.51 and 0.69 ± 0.40 for hyper and medium eutrophication in Lake Taihu,0.78 ± 0.24 in Lake Tianmu,and 0.20 ± 0.04 m-1 in Lake Bositeng,respectively.Correspondingly,aph (675) are 0.59 ± 0.32,0.38 ± 0.23,0.41 ± 0.13 and 0.08 ± 0.02 m-1,respectively.Statistics test shows that phytoplankton absorption of hyper and medium eutrophic Lake Taihu,in addition to light eutrophication Lake Tianmu,is significantly higher than that in mesotrophic Lake Bositeng.Chlorophyll-specific absorption coefficients at 440 nm (aph* (440)) are 0.013 ± 0.006,0.012 ± 0.004,0.038 ±0.008 and 0.051 ±0.013 m2/mgChl.a,respectively.Statistics test shows that aph* (440) of Lake Taihu is much lower than that of Lake Tianmu,and aph* (440) of Lake Tianmu is significantly less than that of Lake Bositeng.The order of the spectral absorption coefficient is as follows:Lake Taihu T Ⅰ ＞ Lake Tianmu ＞ Lake Taihu T Ⅱ ＞ Lake Bositeng,showing that phytoplankton absorption coefficients generally increase with trophic levels,but Lake Taihu T Ⅱ is lower than Lake Tianmu partly due to the high concentration of non-algae suspended matter.In contrast,chlorophyll-specific absorption coefficients decrease with enhanced trophic levels.Phytoplankton absorption coefficients generally increase with trophic levels due to the increase of biomass caused by high nutrient concentration.However,the decrease of chlorophyll-specific absorption coefficients with enhanced trophic level may be attributed to pigment package.%利用太湖和博斯腾湖8月份、天目湖6-8月份的采样数据,开展不同营养状态下浮游植物吸收和比吸收系数的变化规律研究,并探讨其影响因素.利用综合营养指数法,太湖8月42个采样点中20个点为重度富营养,标记为太湖TⅠ,22个点为中度富营养,标记为太湖TⅡ,天目湖夏季、博斯腾湖8月的富营养水平分别为轻度富营养和中营养.440 nm处浮游植物吸收系数aph (440)按照营养水平从高到低由重度富营养到中营养分别为1.02 ±0.51、0.69±0.40、0.78±0.24和0.20±0.04 m-1,相应地675 nm处浮游植物吸收系数aph(675)分别为0.59±0.32、0.38±0.23、0.41 ±0.13和0.08±0.02m-1.统计检验显示,重、中度富营养的太湖以及轻度富营养的天目湖浮游植物吸收系数显著高于中营养的博斯腾湖.440 nm处浮游植物比吸收系数aph*(440)分别为0.013±0.006、0.012±0.004、0.038±0.008和0.051±0.013 m2/mg Chl.a.统计检验显示,重度、中度富营养的太湖浮游植物比吸收系数显著小于轻度富营养的天目湖,而天目湖浮游植物比吸收系数又显著小于中营养的博斯腾湖.另由400～ 700 nm浮游植物的光谱曲线可以明显看出不同营养状态浮游植物吸收系数的变化情况,表现为:重度富营养太湖TⅠ＞轻度富营养的天目湖＞中度富营养的太湖TⅡ＞中营养的博斯腾湖.太湖和天目湖属于富营养化湖泊,浮游植物吸收系数明显高于中营养的博斯腾湖,这充分反映了随营养程度增加,浮游植物吸收逐渐增加.天目湖浮游植物略高于太湖TⅡ是因为太湖非藻类悬浮颗粒物含量高,所以吸收系数偏小.比吸收系数的变化情况与吸收系数的变化情况恰好相反,随着营养程度的增加依次递减.随营养程度增加浮游植物吸收逐渐增加是由于水体营养盐增加促进浮游植物生长,浮游植物生物量逐渐增加所致,而比吸收系数逐渐降低则由于色素包裹效应所致.