Vol. 37 No. 2 Mar Journal of Hydroecology. Karl Karlsson et al 2009 Zhang et al Cao et al 2011

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1 DOI /j Journal of Hydroecology Vol. 37 No. 2 Mar K SD Turb a Chl-a m - 1 < m - 1 < m - 1 < m - 1 a μg /L < μg /L < μg /L < μg /L m < m < m < m mg /L < mg /L < mg /L < mg /L a P < a P < a P < a P < P > a P > P < a Q145 A Karl Karlsson et al 2009 Zhang et al ph PAR PAR PAR PAR Cao et al 2011 PAR 2003 SD PAR ZX baixiaohu0901@ 163. com caote@ ihb. ac. cn PAR ~ μm

2 a Reynolds a 4 Cao et al Fig. 1 Sample site locations in Lake Erhai PAR LI-COR Li a m 7 PAR 2. 5 m m 7 a PAR 4. 5 m 5 30 cm a 1991 Compbell OBS-3A PAR K = lni 0 - lni D D K I K SD 0 PAR I Turb a D D PAR D m K PAR Chl-a R N 3 K

3 Tukey LSD Pearson P > Spss K m - 1 P < P < m m SD 2-A P > SD m - 1 < m - 1 < m - 1 < m - 1 K m SD P < ~ m m - 1 K P < ~ m P < m SD ~ m m - 1 K P > B m < m < m < P < ~ m P > SD m m Tukey LSD P < a Top and bottom of solid bars maximum and minimum values top and bottom of boxes upper and lower quartiles lines in boxes median values letters indicate significant seasonal differences P < Fig. 2 Seasonal variation in water column light attenuation coefficient K water transparence SD turbidity and Chl-a in Lake Erhai

4 a 2-C μg /L < μg /L < a μg /L < μg /L Chl-a P < ~ μg /L K = Turb Chl-a μg /L Chl-a R 2 = N = 132 P < P < ~ P > μg /L a μg /L 2-D a mg /L < mg /L < mg /L < mg /L 2 P < P < P < ~ mg /L HM NM mg /L HM m - 1 NM P < ~ mg /L mg /L m - 1 K HM P > NM P > P > HM NM P < HM mg /L mg /L 1 Tab. 1 Pearson correlation coefficients among optical parameters in Lake Erhai K 1 /SD Turb 1 /SD ** Turb ** ** Chl-a ** ** ** ** P < N N K = 143 N SD = 130 N Chl-a = 143 N turb = 140 Note ** P < sample size are N K = 143 N SD = 130 N Chl-a = 143 N turb = 140. a 1 K Turb Chl-a μg /L μg /L Chl-a a R 2 N P P > Chl-a m - 1 HM m - 1 NM mg /L NM mg /L Turb 2. 2 HM NM P < HM a mg /L NM mg /L Turb Pearson HM NM 1 a P < P > HM NM P > a a P < HM NM P > a P < % 0. 96% 2. 95% a a % a P < Lorenzen 1978

5 Tab. 2 2 Seasonal variation of optical parameters in areas with and without submerged vegetation in Lake Erhai K /m - 1 SD /m Chl-a /μg L - 1 Turb /mg. L ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± * ± ± ± ± ± ± ± ± ** ± ± ± ** ± ± ± ± ± ± ± ± ** * P < ** P < Note * P < ** P < for areas with and without submerged vegetation a P < a 10% Ⅲ a μg /L a a a Reynolds m m a a 2011 a

6 J a J J J J J J J J J J. J J J J J M J J. D J J M.. Cao T Ni L Y Xie P et al Effects of moderate ammo nium enrichment on three submersed macrophytes under J contrasting light availability J. Freshwater Biology J Karl E H Submerged aquatic vegetation correlation with depth and light attenuating materials in a shallow subtropical J lake J. Hydrobiologia /2 / Karlsson J Bystrom P Ask Jsk et al Light limitation J of nutrient-poor lake ecosystem J. Nature J Lorenzen M W Phosphorus model and eutrophication a J. Water Pollution Microbiology J Reynolds C S The ecology of fresh water phytoplankton M. London Cambridge University Press Zhang M Cao T Ni L Y et al Light-dependent phosphate J uptake of a submersed macrophyte Myriophyllum spi J. catum L J. Aquatic Botany

7 Seasonal Variation of Water Column Optical Parameters in Lake Erhai China BAI Xiao-hu 1 2 CAO Te 1 NI Le-yi 1 ZHANG Xiao-lin 1 TANG Xin Donghu Experimental Station of Lake Ecosystems Institute of Hydrobiology Chinese Academy of Sciences Wuhan P. R. China 2. University of Chinese Academy of Sciences Beijing P. R. China Abstract Eutrophication has dramatically changed the optical properties of the water in Lake Erhai. Over the past two decades the lake has gradually transformed from a macrophytic lake into a grass-algae lake because of the continuing deterioration of water quality. Research indicates that recovery of the submerged plant community could improve Lake Erhai water quality and the growth of submerged plants depends primarily on water transparency. In this study seasonal variation of the light attenuation coefficient K water transparency SD turbidity Turb and chlorophyll-a Chl-a were investigated in areas with and without submerged vegetation. Results were analyzed to determine the influence of submerged vegetation on transparency and provide basic data to support eutrophication control in Lake Erhai. Optical properties were monitored and water samples collected at 36 sites 10 sites with and 26 sites without submerged vegetation in April July and November of 2014 and January The light attenuation coefficient K was lowest in spring m - 1 then winter m - 1 autumn m - 1 and summer 105 m - 1. Seasonal change in Chl-a followed the same pattern μg /L spring < μg /L winter < μg /L autumn < μg /L summer. Secchi depth transparency was highest in winter m then spring m autumn m and summer m. Water turbidity was mg /L in spring then mg /L in winter mg /L in autumn and mg /L in summer. As expected the optical properties and Chl-a were closely related. The light attenuation coefficient was significantly correlated with transparency P < r = turbidity P < r = and Chl-a P < r = transparency was significantly correlated with Chl-a P < r = and turbidity P < r = Chl-a significantly correlated with turbidity P < r = In autumn and winter the light attenuation coefficient was significantly lower in areas with submerged vegetation than in areas without submerged vegetation P < but the differences were not evident in spring and summer P > Water transparency and Chl-a between areas with and without submerged vegetation were not significantly different P > but turbidity was significantly lower in areas with submerged vegetation. Key words Lake Erhai light attenuation coefficient transparency Chl-a turbidity submerged macrophytes