Analysis Of Pigment And Methylmercury In Typical Ornithogenic Sediments And Its Ecological Implications

Climate change is a focus of global change research. It is an important issue to human development in the21st century. Late Holocene climate change is the central part of Past Global Changes (PAGES), which is closely related to the evolution of human civilization. Knowledge on the history of climate change in this period can provide us a perspective for understanding and predicting future global climate changes. A number of studies in paleoclimate-environment research at different temporal and spatial scales have been carried out. Since the special geographical and climate conditions, Antarctica and Xisha Islands of South China Sea are sensitive to global climate change and are the ideal research areas for the reconstruction of paleoenvironment. In the present dissertation, we focus on the Late Holocene which is closely related to human activities, and choose several sediment sequences with seabird relics and some environmental media samples (including soil, rock, guano and plant) collected from Antarctica and Xisha Island of South China Sea, respectively. Using multi-disciplinary research method combined with other bio-geochemical indicators to explore the influence of seabird biotransmission on remote ecosystems. Main conclusions of this paper are outlines as follows:1. Comparative study on the analysis method of deposited pigmentThere are many different kinds of methods for deposited pigment analysis. We established HPLC and HPLC-MS method for pigment analysis in lake sediments. HPLC method improves the separation effect of Chlorophyll a and Scytonemin significantly, using methanol and acetone elution solvent with some ion pair buffer solution with a relative standard deviations within10%. HPLC-MS method uses acetonitrile with a small amount of formic acid as elution solvent to improve the ionization efficiency and sensitivity. This method shows fine separation effect, abundance and the stability. Compared with other methods, including UV-Vis spectrophotometry and near-infrared reflectance spectroscopy (NIRS), HPLC-MS is proved to be superior. Although different methods have shown a relatively reliable analysis results, there are still some differences in analysis method and effects. NIRS just can be used as an indirect method for rapid assessment of chlorophyll a content. The equipment and operation of UV-Vis spectrophotometry is relatively simple and timesaving, but the accuracy is not high enough, and the specificity is relatively poor. The HPLC method demands strict chromatography conditions, and it is very difficult to separate all the pigments by HPLC. The requirement of separation effect by HPLC-MS is not so rigour, and HPLC-MS is more sensitive, rapid and accurate compared with other traditional methods.2.800-year UVR record of the Ross Sea area, East AntarcticaWe used high performance liquid chromatography (HPLC) combined with mass spectrometry (MS) to analyze deposited pigments (including chlorophyll a, chlorophyll b, canthaxanthin, echinenone, zeaxanthin, scytonemin and mycosporine-like amino acids) in two sediment cores collected from the Ross Sea area, East Antarctica. We explored the sources and characteristics of each pigment, reconstructed an800-year record of ultraviolet radiation (UVR) and total incoming light intensity (UVR+PAR (photosynthetic active radiation)), and assessed the possible factors that have influenced UVR changes in this region. The results indicated at least four UVR peaks during the past800years, corresponding to0-50a BP,250-320a BP,350-450a BP and520-610a BP, with the intensity from the most recent sediments being the highest. A comparison of two proxies for UVR and UVR+PAR indicated a similar pattern between190and320a BP, suggesting that factors controlling the UVR intensity in the Ross Sea area may be related to changes in insolation during the Little Ice Age. Both of these proxies are, however, weakly correlated during other periods and the reconstructed UVR and solar activity records indicate some negative correlation. Historically, the inverse correlation between these two parameters may be a natural process, but during the modern period, this process was strongly affected by anthropogenic activities.3. The application of near infrared reflectance spectroscopy in the reconstruction of lake primary productivity in East Antarctic areaThe near infrared reflectance spectroscopy (NIRS) was determined in five sediment profiles collected from East Antarctica, and the potential application of NIRS in reconstructing historical changes of Antarctic lake primary productivity was studied. Meanwhile, we explored the environmental implications of spectral data using statistical analysis method. The results showed that the appearance of trough at650-700nm is an important marker for distinguishing the sedimentary organic matter source from between guano and algae. The measured chlorophyll a content had significantly positive correlations with the trough area between650-700nm, and no distinct trough was found in the sediments with organic matter completely derived from guano. Modeling results showed that the spectro-inferred chlorophyll a content and the measured data have consistent change trends versus depth, and thus the dimensionless trough area could be used as an independent proxy for rapidly reconstruction for the historical fluctuation of Antarctic lake primary production. The principal component analysis (PCA) of MC2sediment profile showed that the factor loadings of PCA displayed similar change pattern with S2index, a reliable proxy for the change in historical lake primary productivity. Compared with trough area method, PCA statistical approach was more accurate. Combined with the spectrum of environmental media (soil, guano and algae), we explored the proportion of each substance (soil, guano and algae) in the bulk sample and established statistical models between chemical element content and spectral indices using PCA and PLS (Partial Least Squares) methods.4. The application of sediment pigment in the reconstruction of algae community structure in East Antarctica lakesDeposited pigments were analyzed using high performance liquid chromatography (HPLC) combined with mass spectrometry (MS) on three sediment cores from the Ross Sea area, East Antarctica. Based on the CHEMTAX analyses, we reconstructed the record of algae community in East Antarctica lakes and examined the effects of seabird activity on lake primary productivity and algae community structure. The results showed that there were several algae classes in the study area, including cyanophyta, cryptophyta, chlorophyta, diatom and pyrrophyta, where chlorophyta, cyanophyta and diatom were the dominant classes. The positive correlation between chlorophyll a and P concentration indicated that the input of seabird droppings promote the growth of algae and improve lake primary productivity. Chlorophyta is the main species in BI and MB6profiles, and its abundance is significantly higher than the others. Combined with other geochemical indicators, we found that the influence of seabird activity in BI and MB6profiles was higher than CL2core. Higher nutrient content enhances algae biomass, in particular, promotes the growth of chlorophyta. The remarkable positive correlation between chlorophyll a and chlorophyll b (r=0.86, n=40and r=0.84, n=29) in BI and MB6cores further confirmed that.chlorophyta is the dominant species. The input of seabird droppings can cause competition of algae in lakes, leading to the change of community structure. Although there are certain deficiencies in CHEMTAX program, it can be a relatively more accurate in characterizing the abundance of dominant alage species in the study area, and is currently one of the most widely used methods.5. The impact of Seabird biotransmission on methylmercury distribution in Xisha Island ecosystemWe established the analytical method for the determination of methylmercury in seabird excrement and ornithogenic sediment samples using atomic fluorescence spectroscopy coupled with microwave-assisted extraction. Using this method, we determined the distribution and main source of methylmercury in ornithogenic coral sand sediments and pure guano collected from Guangjin and Jinqing islets of the South China Sea and explored the impact of seabird biotransmission on remote Xisha Island ecosystem. Results showed that the levels of MeHg, total Hg (THg) and the proportions of MeHg in THg (%MeHg) are very high in both fresh and ancient guano samples.%MeHg in ancient guano exceeded70%, much higher than that in fresh seabird droppings (-45%). These results suggest that excreting feces likely plays an important role in the cycling of MeHg in seabirds. MeHg concentration has significant positive correlations with THg and TOC, suggesting that MeHg in the ornithogenic sediments probably shares a common source with THg and TOC. The correlation between MeHg and P indicates that guano input is the dominant factor controlling the concentration of MeHg before the Industrial Revolution, but the emission of modern Hg pollutants derived from human activities might have significant effects on post-industrial MeHg distribution in seabird droppings and ornithogenic sediments through biomagnification and biotransport.%MeHg in the ornithogenic coral sand sediments is extremely high, ranging from10%-30%with an average of～20%. Furthermore, older guano and ornithogenic sediment samples generally have a larger proportion of MeHg in THg. Combined with lack of influence from microbial activity, guano was identified as the major source of MeHg in the ornithogenic coral sand sediments in the Xisha Islands. Though the input of seabird-derived nutrients promote the development of coral island ecosystem, it also transports a lot of pollutants into remote island ecosystem, threating the health of residents on the island.