| This study was one of the important components, comprised of one section in "Study on technology to control the pollution of cyanobacterial bloom in Dianchi lake", a special grand national science-technology project. The demonstration area situates on the north-eastern of Dianchi Lake, which located in the south of Kunming, the capital city of Yunnan Province in south-west of China. The cyanobacterial bloom occurs almost annually in the area, one serious hyper-eutrophication part of the lake. The results of the study on primary production and its influence factors in demonstration area with the methods of field investigation & laboratory test are reported in this thesis as following below.1. The phytoplankton primary production of demonstration area: The annual average of gross primary production (GPP) of water column is 3.88 g O2 m-2.d-1 in 2002, and 4.95 g O2.m-2.d-1 in 2003. The most of annual GPP in test area is central on March to October, the maximum value in the end of spring and the beginning of summer, and autumn. The GPP in layer of 0-0.5m is 74% of the total in water column, 21% in 0.5-1.0 layer, and 5% in 1.0-2.0m. Exception of some months, the maximum GPP value was in surface layer. The depth of light compensatory point is higher during dry season, and lower during monsoon season. The ratio of P/R is 2.1-5.4 above 0.5m layer, less than 1.0 below 1.0m layer. The ratio of P/B is 0.261. 2.The effects of irradiance and phytoplankton biomass (Chla) on GPP: The light-saturated of photosynthesis (Ik) of microcystis colony is 25491ux. Below the irradiance of Ik, the GPP are affected with the light intensity and Chla concentration. Above the Ik, the GPP of a unit of Chla decreases as the Chla concentration is increased.3.The promotion of sewage on algal growth: The untreated sewage from the inflow river stimulate the growth of the algae cyanobacteria Microcystis and green algae Scenedesmus, the relationship equation between the promotion rate (y) on Microcystis aeruginosa (MA) and sewage dilution rate (x) is y=3.0905x+0.0668,R2=0.9886, x=0-0.5; the relationship equation between the rate (y) on Scenedesmus sp and the dilution rate (x) is y=2.0132x+0.4101,R2=0.9653, x=0-0.9.4. Variation of GPP and the impact factors during day and night: The most of the whole day GPP in sampling sites are central on during 8:30to 18:30, which is 80% ofthe total GPP. The lake current leads algal bloom accumulation in demonstration area, to have largely decrease of irradiance below the water surface, the reduction of phytoplankton GPP about 36%. The dissolved oxygen in water are increased with wind and waves, thus there is an even distribution of DO in the water layers. 5.The GPP in enclosures: Comparison with the enclosure CK, the GPP in three treatment enclosures with incubating common carps and planting macrophytes is reduced in certain degree, it is decreased about 31% in the enclosure of (75g carp+grass).There is a season alternation of GPP in different water layers only the enclosure with (100g carp+grass), reduced 3% in surface layer and increased 5% in 0.5m layer.6.The biomass (Chla) and GPP of various size fraction in enclosure: There is an obviously regulation on the distribution of GPP and biomass among the various size fractions in enclosure with (lOOg carp+grass). The phytoplankton biomass (measured with Chla) and GPP is reduced 12 and 10 in percentage points respectively on the fraction size larger than 50 u m; those is increased 11 and 10 in percentage points respectively on the fraction size less than 50 u m in the enclosure. 7.The biomass (Chla) and GPP of various size fraction in demonstration area: Comparison with the controlled sampling site outside the demonstration area, there is an obviously regulation on the distribution of GPP among the various size fractions in the 6.01 km2 area with (294t carp+grass) during August to October in 2002. The phytoplankton GPP is reduced 18 in percentage points in the fraction size larger than 50 u m; those is increased 81 in percentage points in the si...
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