Comparison Studies Of The Pre-treatment Methods Involved In The Lipid Research In Liangzi Lake

The Lacustrine deposit, usually with rapid sedimentary rate and continuous sediment which has long time span and ample information therein, thus is a good achieve of regional even global paleoevironment and paleoclimate information. It almost records the whole evolutional pathway, within its sedimentation lifetime, of climates, vegetations and human activities in the region it located. It showed by the past work that the lacustrine sediments responds to the regional climate change so sensitively that it can capture the paleoclimate event at a hundred even decade scale, so it's a idle material for the regional paleoenvironment and paleoclimate reconstructions.Most of researches hitherto focus on lacustrine sediments mainly employs traditional methods such as the analysis of sediment grain size, palynology, biological remnant, pigment. Bacteria and algae thriving are the causer of water bloom. But these microbes are seldom preserved in the body fossil form, and meanwhile some indicators bacteria and algae such as pigments are difficult to get a high resolution. Hence when uncover the hidden record of past water bloom in the lacustrine sediments, the traditional methods have obvious limitation can't over come now. Luckily, lacustrine lipids can meet this need instead. The biomarker can indicate lake algae and bacteria ecosystem evolution at a taxonomy scale so that to elucidating the ecosystem structure changes. Thus lipids in the lacustrine sediment originate from higher plants and algae are good proxies of regional climate and environment changes and human activity, and it has already been widely used in reconstruction of paleoclimate and paleoenvironment and global change. Within these biomarker proxies, those from microbes, especially bacteria are far more sensitive to climate and environment changes, and they even have higher resolutions. Till now, combined with other environmental indicators, lacustrine lipids have evident advantages when utilized to reconstruct the paleotemperature, paleorainfall, paleosalinity, paleoproductivity and ancient human activity. Well, at the same time, there's still certain tough unavoidable, that is to say that the lacustrine lipids can not be extracted and analyzed easily, and that experiment protocols employed and the virtual processes would affect the precision even the accuracy. Therefore, it's very important to find out the best pretreatment method of lacustrine lipids analysis.Lake in the middle area of Yangtze River is one of the weakest ecosystems, and the most serious environmental problem of the lake confronted is eutrophication. Liangzi lake is typical one of this kind. Once, it was one of the best environment protected lake in Hubei province. However, in last century, reclaiming land by filling the margin part of the lake and long-term waste water drainage from chemical industry to the lake, water quality decrease gradually.Object of this research is sediment cores get from Liangzi Lake, Sample divided into two parts: Before analysis, the first part (labled as LF) is air dried in room temperature, and extracted by ultrasonic method then separated by elute through the silicon gel column, converted to by their silane derivative. Differently, the second part (labled as .LF) is preserved under low temperature immediately after cored, and pretreated by freeze drying, ultrasonic extraction, derivatization with TMS as a whole without the separation by silicon gel column. Through two-part comparison of the lipids analysis result, namely the n-alkane distribution pattern such as chain length range, peak mode, average chain length(ACL), carbon preference index(CPI), the absolute abundance of n-fatty acids, n-alkanol, sterols and hopanoids, we found the different results of lipid analysis is caused by the distinct pretreatment methods, and we got a optimal pretreatment method including the sample preservation and component extract when deal with the lake sediment sample with abundant microbe lipid.1.Cryopreservation and freeze drying is good for the preservation of the organic matters of lacustrine sediments relative to the oven dry and air dry. The latter two method would change the origin constituents of the lipids and lead to their decreasing or decomposition, as showed by the reduced CPI value of n-alkane and absolute lipid abundance, what's worse the severe losing of certain unstable components (such as the n-fatty acid). Without a column separation before dirivatization, it would enhance the coefficient of recovery; this is very helpful for the lower lipids content samples, although it brings many difficulties about the peak identification. The details of the experiment processes are decided according to the specific samples.2.The sample from Liangzi Lake could reflect the original information on sedimentary environment. A series of normal alkanes, fatty acids, alcohols, n-alkan-2-ones, wax esters, steroids and terpanes are detected from the sedimentary samples. The CPI (carbon performance index) was constant indicating the microbial degradation and diagenesis did little effect on the samples. Alcohols, including fatty alcohols, sterols and hopanols, are the predominant compounds. The n-alkanes, n-alcohols and n-alkan-2-ones with longer carbon chain, had a distinct odd-even predominance pattern, indicating higher plants inputs. C28:2Δ5,22 sterol originated from diatoms, 2-Methyl hopanol and 4,23,24-trimethylsterol can indicate cyanobacteria and dinoflagellate, respectively. C27, 1Δ5 sterol can indicate zooplanktons or phytoplanktons. Hopanols, hopenes and hopanes with high distribution and different kinds could be the contributions from microorganisms living in the watershed.3.Multidisciplinary analyses, including radionuclide dating (Pb-210), aquatic marcrophytes, ostracods, gastropods, amoebas, pigment and organic carbon isotope, have been employed to investigate the samples from Liangzi Lake. In reference with historical data, the development is divided into three stages: (1) The first stage is before 1950 AD. There are various kinds of auatic organisms, the qualityof environment is pretty good. (2) The second stage is from 1950 AD to 1990 AD. Bacteria and algae step into development. Human activities brought great effects to this lake, such as aquaculture, the discharge of domestic sewage and building dykes to reclaim land from a lake.(3) The third stage is from 1990 AD. The amount of bacteria and algae hit an all-time high. More nutrition was introduced into these lakes, causing serious eutrophication and pollution that destroyed native aquatic plant ecosystems.4. The koprosterol from water accompanied with other sterols including cholesterol, sitosterol and dihydrocholesterol) may orignated from human waste and animal feces. The water body discharge without treatment would be another reason, which was one of the human factors leading to the eutrophication of Tai Lake. In order to prevent Liangzi Lake becoming the second "Tai Lake", ,the restoration of water ecological environment of lake is the emphases of our future work.