Phytoplankton absorption and chlorophyll-specific absorption coefficients characteristics of different trophic level lakes

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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 includeshyper and medium eutrophication zones.Meanwhile,Lake Tianmu and Lake Bositeng are light eutrophic and mesotrophic,respectively.Phytoplankton absorption coefficients at 440nm(aph(440)) are 1.02±0.51 and 0.69±0.40 forhyper 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 ofhyper and medium eutrophic Lake Taihu,in addition to light eutrophication Lake Tianmu,is significantlyhigher than that in mesotrophic Lake Bositeng.Chlorophyll-specific absorption coefficients at 440nm(a*ph(440)) are 0.013±0.006,0.012±0.004,0.038±0.008 and 0.051±0.013m2/mgChl.a,respectively.Statistics test shows that a*ph(440) of Lake Taihu is much lower than that of Lake Tianmu,and a*ph(440) of Lake Tianmu is significantly less than that of Lake Bositeng.The order of the spectral absorption coefficient is as follows: Lake Taihu TⅠLake Tianmu Lake Taihu TⅡ Lake Bositeng,showing that phytoplankton absorption coefficients generally increase with trophic levels,but Lake Taihu TⅡ is lower than Lake Tianmu partly due to thehigh 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 byhigh nutrient concentration.However,the decrease of chlorophyll-specific absorption coefficients with enhanced trophic level may be attributed to pigment package.