Search

Lake Gehu is a representative shallow lake located in the downstream of Yangtze River in China. To identify the phytoplankton community distribution after its treatment,a survey was conducted on the phytoplanktonic community and environmental factors in its north part from January to December in 2013. According to the survey,there were altogether seven phylum,fourtythree genus and sixty-one species of phytoplankton,mainly with Scenedesmus and Cyclotella in spring and winter,Microcystis and Melosira granulata in summer and autumn. The maximum phytoplankton biomass during sampling period was 90. 6 mg / L in August,mainly with Microcystis aeruginosa. The average density of phytoplankton showed a decreasing trend from west to east,with lower vegetation coverage in the open water area. The environmental factor analysis indicated that total nitrogen,total phosphorus and water temperature were key factors that influence the phytoplanktonic density and biomass in this area. Comparing with the average biomass in the water chestnut area and reed area with that in the untreated open water area in the same month,we found that the water chestnut area decreased with the range of 72. 7%-91. 1%,and 63. 9%-83. 7% in the reed area. In August and September when algal bloom occurred in the open water area,the biomass in the chestnut area and in the reed area was only 14. 6% and30. 3% of that in the water area,respectively.

The spatial distribution, temporal changes of water transparency and their influencing factors in Lake Fuxian, a deep lake in Yunnan Plateau, were analyzed according to the investigations during June-July in 2005 and the regular monitoring data since 1980. The Secchi disk transparency varied from 0.5-6.2m with an average value of 4.6m in Lake Fuxian during June-July in 2005, The spatial distribution pattern of transparency was: north areasouth area, littoral zonepelagic zone, and very low in the estuary area. Suspended solid and algae were the main influencing factors on spatial distribution of water transparency which decreased with their increase. In the last 20 more years, water transparency in Lake Fuxian showed decrease trend, and the increase of algae was the main direct influencing factor. The increase of total nitrogen and total phosphorous was the important indirect influencing factors which could lead to algae multiplication.

A concept Aerated Vertical-Flow Wetland is introduced in the text,experimental researches through a pillared unit were carried out on the performances of treating domestic wastewater in the rural area of Lake Dianchi valley,Yunnan province.The oxygen transfer efficiency of the experiment device reached 14.04%.And the experiment data showed that,with hydraulic loading as 15.29m~3/(m~2·d)and airflow-waterflow ratio 1:2,average BOD_5 and NH_4-N removal respectively reaches 74.4% and 63.5%.The BOD_5 and NH_4-N values within outflow get to 4.96mg/L and 2.72mg/L.It resulted that,the Aerated Vertical-Flow Wetland Technics was effective and economical for suburb domestic wastewater treatment with high hydraulic loading.

Nine sediment-water columns were taken from three stations of East Taihu Lake (about lm in depth) in June, 1997. The overlying water of the cores was filtered (0. 45m), and then the cores were placed in a dark room for 50 days. Air-bubbling was used to keep oxidized conditions in the overlying water and upper sediment, without resuspending the sediment. The room temperature was between 23. 5 and 31. 2, and the pH value of the overlying water and upper sediment was 7. 2 0. 2. Concentration of PO_4~3-P in the overlying water was measured every 2 or 3 days to follow the P-release process. In the first 15 days, PO_4~3 -P level in the overlying water increased 2 orders of magnitude. But in the following 33 days, the PO_4~3-P level decreased 1 order of magnitude and then stabilized. Such a process was also found in the West Lake, Hangzhou and Gehu Lake, Changzhou. We think it not a normal sediment-P-release process, but more complex as follows. In natural conditions of East Taihu Lake, the sediment is covered by a layer of detritus. Biological degradation is so intensive in this layer that PO_3~4 accumulates to a high level and diffuses to both the overlying water and the sediment beneath it. In the sediment a steep PO3~4 -P concentration gradient forms because of the high diffusive resistance. But in the overlying water, PO_4~3-P is used by aquatic plants and is kept at a low level. We are not able to measure PO_4~3-P concentration in the detritus layer, but an indirect evidence was found in the same lake: a PO_4~3- P concentration gradient from 200mg m_~3 in the upper sediment layer to 80mg m_~3- in the sediment of 18cm depth existed when PO_4~3-P concentration in the overlying water was only 22 mg m_~3. In the core experiment, phosphorous biological cycling was broken when phytoplankton was removed from the overlying water by filtration, and thus, PO_4~3- accumulated in the water quickly; After 15 days, the p-release reaction in the detritus layer was about to end, and p-diffusion from overlying water to the sediment triggered. In East Taihu Lake and the other similar lakes with stable bottom conditions, detritus layer may exist and affect p-release core experiment seriously. In such a situation, it is better to measure internal-P-loading by other means, such as whole lake p-budget and in-situ enclosure experiment.