Kong Fanxiang

China's lakes at present: Number, area and spatial distribution

Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM, changes in the spatial characteristics of all lakes in China were determined following pre-established interpretation rules. This dataset was supported by 6843 digital raster images (1:100000 and 1:50000), a countrywide digital vector dataset (1:250000), and historical literature. Comparative data were corrected for seasonal variations using precipitation data. There are presently 2693 natural lakes in China with an area greater than 1.0 km2, excluding reservoirs. These lakes are distributed in 28 provinces, autonomous regions and municipalities and have a total area of 81414.6 km2, accounting for ∼0.9% of China’s total land area. In the past 30 years, the number of newly formed and newly discovered lakes with an area greater than 1.0 km2 is 60 and 131, respectively. Conversely, 243 lakes have disappeared in this time period.

Spatio-temporal distribution of cyanobacteria blooms based on satellite imageries in Lake Taihu, China

Of all the cloudless 340 satellite imageries 11 were shot by Landsat MSS/TM/ETM sensor since 1979, 216 by EOS MODIS sensor since 2002, 10 by CEBERS CCD sensor since 2005 and 3 by IRS P6 LISS-3 sensor in 2007. On the basis of the spectral analysis, an applicable model was developed to extract the cyanobacteria bloom information from multi-source remote sensing images. And then, the model was used to acquire cyanobacteria bloom-covered area and its spatial distribution. The result showed that the initial time of cyanobacteria bloom was moved from June or July to March or April at present, three-four months advanced than the normal. The statistics showed that the cyanobacteria bloom occurs most frequently in June or July and the second was in October or November. Additionally, the duration of cyanobacteria bloom is becoming longer and longer and almost over time of March to December at present. The most intensity of cyanobacteria bloom occurred in September and the second was in June. The north of Lake Taihu, including Meiliang Bay and Zhushan Bay, was the initial location of cyanobacteria bloom and also the heavy disaster area, where the cyanobacteria bloom occurred every year since its first time. However, cyanobacteria bloom also occurred along the south bank of Lake Taihu almost every year since 2001, where the cyanobacteria bloom-covered area was becoming larger and larger and the duration time was becoming longer and longer, and which was becoming the earliest location of cyanobacteria bloom. It was noticeable that the cyanobacteria bloom was pervading gradually from the north, the west and the south to the center since 2003, and it sometimes covered almost the whole non-vegetation area. Additionally, there were cyanobacteria blooms occurring at Gonghu Bay since 2005, and it occurred more frequently in 2007.

Relationship between bacterioplankton and phytoplankton community dynamics during late spring and early summer in Lake Taihu, China

Abstract The relationship between bacterioplankton and phytoplankton community compositions was investigated from April to June, 2005 with samples taken at five different stations in Lake Taihu, China. Bacterioplankton and phytoplankton community compositions as determined by denaturing gradient gel electrophoresis of polymerase chain reaction amplified bacterial 16S rRNA gene fragments (PCR-DGGE) and microscopic examination, respectively, revealed a high degree of diversity. In total, 43 unique bands were identified amongst the DGGE profiles, and 29 dominant phytoplankton populations were observed. The DGGE profiles were clustered into two distinct groups. These two clusters were closely associated with two dominant phytoplanktons, Ulothrix sp. and Microcystis spp., as observed on April 19, May 27 and June 27, 2005, respectively. The relationship between bacterioplankton and phytoplankton community compositions was investigated using Canonical Correspondence Analysis (CCA) with the Shannon-Wiener diversity index of phytoplankton community (Hp), the total cell abundance of phytoplankton (N) and the relative abundance of Microcystis spp. (M) as the variables. The CCA results indicated a 30.9 % correlation coefficient, suggesting a high degree of correlation between bacterioplankton and phytoplankton community compositions.

Effects of rice straw on the cell viability, photosynthesis, and growth of Microcystis aeruginosa *

Rice straw is supposed to be an environment-friendly biomaterial for inhibiting the growth of harmful blooms of the cyanobacterium Microcystis aeruginosa. However, its potential mechanism is not well known. To explore this mechanism, the growth, cell viability (esterase activity, membrane potential, and membrane integrity), photosynthesis, and cell size of M. aeruginosa were determined using flow cytometry and Phyto-PAM after exposure to rice straw extracts (RSE). The results show that doses from 2.0 to 10.0 g/L of RSE efficiently inhibited the alga for 15 days, while the physiologic and morphologic responses of the cyanobacteria were time-dependent. RSE interfered with the cell membrane potential, cell size, and in vivo chlorophyll-a fluorescence on the first day. After 7 days of exposure, RSE was transported into the cytosol, which disrupted enzyme activity and photosynthesis. The cyanobacteria then started to repair its physiology (enzyme activity, photosynthesis) and remained viable, suggesting that rice straw act as an algistatic agent.

Nitrogen stable isotope study on nitrate nitrogen pollution of four inflowing rivers of Lake Chaohu

Nitrogen isotopic technique was used to study the nitrate pollution of four inflowing rivers of Lake Chaohu in different seasons.Our results showed that River Shiwulihe was the most polluted river,while River Shuangqiaohe as the least polluted one.Nitrogen Stable isotopic values demonstrat that nitrate sources differ in various seasons for those four rivers.The dominate pollution sources of nitrate for River Shiwulihe and River Nanfeihe are human sewage and industry discharge.In the case of River Paihe,nitrate is mainly derived from industry discharge in winter,which is originated from agriculture and rainfall in spring and summer,respectively.For River Shuangqiaohe,nitrate contamination is mainly caused by agriculture in winter and spring,but is influenced by rainfall in summer.In addition,our results imply that ammonium is the main nitrogen pollution compound in those four rivers,and δ15 NH+4 value should be detected for the identification of ammonium sources in further study.

Genetic diversity of photosynthetic picoeukaryotes in Lake Taihu

Genetic diversity of photosynthetic picoeukaryotes has been investigated at two stations located in Meiliang Bay and East Taihu in Lake Taihu,respectively.Genetic libraries of chloroplast 16S rRNA gene have been constructed by using primer set PLA491F/OXY1313R,biased towards chloroplast of marine algae.The results show that most of photosynthetic picoeukaryotic sequences belong to Cryptophyta,and the rest of them are affiliated with Bacillariophyta,Chrysophyta and Haptophyta.The study can help us take knowledge of the community structure and ecological function of phytoplankton in Lake Taihu.

Spatial variations of the over-winter cyanobacterial in Lake Taihu

In order to investigate the spatial variations of the over-winter cyanobacteria in different areas of Lake Taihu, sediment and water samples were collected monthly in 14 sites in winters from 2007 to 2008. The phycocyanobilin concentration (PC) of samples was measured by the fluorometry analysis of pigments to confirm the difference of PC’s spatial variations among three areas of Lake Taihu. The result shows that, differing from summer, the winter PC in both sediment and water from northern part was lower than western and southern part of Lake Taihu. Even in December, in some parts of western and southern areas the cyanobacteria was still blooming, and PC of surface sediment was also high. According to the result, it is clear that the over-winter cyanobacteria was mainly distributed in western and southern areas of Lake Taihu during the investigation winter seasons.

Changes in structure and element composition of mucilage sheath of Microcystis colony during the bloom decline period

Mucilage sheath is critical for maintaining predominance of colonial Microcystis in eutrophic freshwaters. To explore mechanism underlying the decline of Microcystis bloom, colony size, polysaccharide content and sheath structure of Microcystis colo⁃ nies were investigated from October to January when the bloom decline. The results indicated that the proportion of Microcystis with colony size larger than 180 μm decreased, while colonies in the 100-180 μm size range increased. Polysaccharide content per cell decreased during the decline period. The scanning electron micrograph showed that sheath structure of Microcystis colonies changed from complete to broken. Element analysis of the surface of Microcystis colonies showed the percentages of Na and P decreased grad⁃ ually, Al and S fluctuated, while Ca and Si increased. These results indicated that changes in polysaccharide content and element composition of colony sheath accompanied with colonial Microcystis disaggregation, and thus led to bloom decline.

Application of flow cytometry to enumerate small plankton

The small plankton( cell size less than 20 μm) plays an important role in the circulation of materials and energy flow of the aquatic system. Accurate enumeration of these organisms is the basis for understanding their ecological role in various water bodies. In comparison with microscopy observation,flow cytometry analysis is much more advantageous in terms of speed,sensitivity and accuracy. Moreover,multiple parameters of a single cell could be measured simultaneously using flow cytometry. The protocol to enumerate plankton depends on the type of plankton. Discrimination of several major groups of phytoplankton is mainly based on the differences in the fluorescence properties of their photosynthetic pigments. While for the heterotrophic bacteria,protozoan and viruses,a combination of exogenous fluorochromes staining on cell components( mainly nucleic acids) is required to better characterize different cell groups. Now flow cytometry has become a routine methodology for detecting density of the autotrophic phytoplankton and heterotrophic bacterioplankton. However,it has been only used in quantification of protozoan and viruses in the recent 10 years,for those applications which are much more difficult and complicated for the larger cell size and less abundant densities of protozoan and much smaller cell size( even smaller than the wavelength of the laser light used) of viruses compared to bacterioplankton and small phytoplankton. The different principles and protocols used to discriminate autotrophic phytoplankton,heterotrophic bacteria,protozoan and viruses through flow cytometry were reviewed in detail,and future applications of flow cytometry in aquatic microbiology were also prospected.

Progress and prospect of research on cyanobacteria nitrogen fixing in aquatic ecosystem

The predominance of nitrogen fixing cyanobacteria in the eutrophic aquatic systems is related to many environmental factors,such as nutrient forms and concentrations,nitrogen to phosphorus ratio,water temperature and trace metal.The nitrogen fixing cyanobacteria dominated in lakes with the concentration of orthophosphate above 0.01mg / L,the concentration of dissolved inorganic nitrogen under 0.1 mg / L,furthermore,the lower ratio of nitrogen to phosphorus was suggested to indicate the occurrence of the nitrogen fixing cyanobacteria,but the differentiation mechanism of nitrogen fixing and non-nitrogen fixing cyanobacteria need a deep research.Moreover,cyanobacteria nitrogen fixing rates can be influenced by the light availability,inorganic nitrogen concentrations,heterocyst abundance and the fixed nitrogen determines the contribution to the pools of nitrogen.The nitrogen fixing cyanobacteria is the important contributor to the pools of nitrogen in the ocean systems,but in the eutrophic lakes,its contribution is still in dispute.Thus,this paper reviewed the researches on nitrogen fixing cyanobacteria to attract attention of scientist on its important contribution to the pool of nitrogen in aquatic systems.