| Lake Chenghai,one of "the nine large plateau lakes" in Yunnan Province,provides various natural resources for the local inhabitants,but have been suffering from deterioration of water quality and aquatic ecosystem.Although several studies have examined the climate,sediments,aquatic vegetation,primary productivity,algal blooms and eutrophication in the lake since the 1980s,the optical property(e.g.,euphotic zone)as well as the overall knowledge of primary productivity remain unclear.Thus,the temporal-spatial distribution of euphotic depth and phytoplankton primary productivity and their potential influential factors were analyzed in this study,based on the field and model(i.e.,vertically generalized production model,VGPM)investigation from April 2016 to February 2017 in Lake Chenghai.The main results,followed as below,would be worth for lake protection.(1)During the study period,the average value of PAR attenuation coefficient is 1.09 ± 0.28m-1;the mean of euphotic depth(Zeu)of Lake Chenghai is 4.47±1.16m.In the aspect of space,the maximum euphotic depth is 4.39±0.82m at 4#,and the minimum value is 3.79±1.15m at 9#.The distribution of euphotic depth is:Central>North>South.From the perspective of monthly changes,the maximum value is 6.40±1.02m in May 2016,the variation range is 5.18?8.74m;the minimum is 3.56±0.49m in July 2016,the range of variation is 2.89-4.17m.There is a significant negative correlation between the euphotic depth and concentration of chlorophyll a,and a significant positive correlation with the transparency.And there is no significant correlation between the concentration of suspended matter and permanganate index.(2)In situ measurement of primary productivity at the dock of Lake Chenghai(in black and white bottle method).The mean of gross primary productivity of the water column is 5.40g/(m2 d),and the maximum value is 9.40g/(m2·d)in November 2016,The minimum value is 2.71g/(m2·d)in April 2016;the mean of net primary productivity of water column is 2.36g/(m2·d),and its change trend is consisitent with that of goross primary producttivity,the maximum value is 4.62g/(m2·d)in February 2017,the minimum value is-2.8g/(m2·d)in July 2016;the mean of respiration consumption of water column is 2.91g/(m2·d),The maximum value is 9.85g/(m2·d)in July 2016,the minimum is 0.08g/(m2·d)in April 2016.In the vertical distribution,the maximum of the primary productivity always appears at depthod 0.5 m,and a small part appears at depth of 1m,and then the primary productivity decreases significantly as the depth increases.There is a significant linear relationship between gross primary productivity and concentration of chlorophyll a(GPP=0.024+0.052Chl.a,R2=0.8086,P<0.01).(3)The comparison between the model estimates and the measured values of the primary productivity shows that there is a significant correlation between the two,and the trend is highly consistent.By inputting the parameters into the VGPM for calculating the results of the whole lake:from April 2016 to February 2017,the mean of the primary productivity is 4.97±2.00g/(m2·d),and the variation was 1.81 g/(m2·d)?10.29g/(m2·d).The minimum value is 4.39±2.02g/(m2·d)at 9#,and the maximum is 5.53±2.16g/(m2·d)at 8#.From the point of space:North>South>Central,the values are 5.58·1.94g/(M2·d),5.04±2.24g/(m2·d)and 5.00±2.15g/(m2·d).After testing,the gross primary productivity of Lake Chenghai has significant correlation with the concentration of chlorophyll a and transparency. |
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