Effects Of N,P,Si And Fe On The Growth And Lipid Content Of Algae And Its Significance For The Petroleum Geology

A large number of exploration practices have found that many of the main basins in China are accompanied by volcanic material deposition.The role of volcanic activity in the formation of oil and gas has also attracted extensive attention from scholars at home and abroad.As a common geological activity in nature,volcanic activity not only plays an important role in forming favorable reservoirs and promoting hydrocarbon generation evolution of source rocks,but also plays an important role in the formation of organic matter and oil and gas.It has been found that the descent or deposition of volcanic material from land or underwater eruptions is an important nutrient source into the ocean waters and can significantly promote the growth of Marine algae.Marine algae is the main plant of petroleum formation and the main source of organic matter on earth,which is of great strategic significance in the energy industry.In this study,spirulina sp.,chlorella sp.,Scrippsiella trochoidea and Chaetoceroides were taken as the objects,and the changes of algal biomass and total lipid content under different nutrient concentrations were studied by single factor experiment,optical density method,hydrochemical analysis,physiological and biochemical research methods,etc.This paper reveals the influence of nutrient elements N,P,Si and Fe commonly released by volcanic materials on Marine algae,and expounds the"fertilization"effect of volcanism on the parent material of hydrocarbon generation,so as to discuss the influence of volcanic materials on the formation of oil and gas,so as to provide a new basis for the prediction of hydrocarbon source rocks and petroleum exploration and development.In this study,the growth of algae was measured by optical density method,and the concentration of target elements in the culture medium was regularly detected.The results showed that N,P,Si and Fe were important factors that determine the growth of Marine algae,and they could significantly promote the growth of algae,and the biomass increased with the increase of concentration in a certain range.The influence of N and P is more significant.Si had greater influence on Chlorella,but not on Spirulina sp.,Chlorella sp.,and Scrippsiella trochoidea.The optimal concentration of NO₃-N was 12 mg/L～60 mg/L.The number of algal cells in normal F/2 medium was 8.17～22.35 times that in n-restricted culture.The optimal concentration of PO₄-P was 0.56 mg/L～5.6 mg/L.The number of algal cells in normal F/2 medium was16.5～26.67 times that in phosphorus restricted culture.The Si element has a great influence on the growth of Scrippsiella trochoidea.There is no obvious effect on Spirulina sp.,Chlorella sp.,and Scrippsiella trochoidea.In the experiment,the optimal Si O₃-Si concentration of Scrippsiella trochoidea was 5 mg/L,and the maximum cell density was 8.3×10⁵ cells/ml.The optimal Fe Cl₃ concentration of each alga is different.Spirulina sp.grows well in the range of 0.6～2.4mg/l,with the maximum cell density of 5×10⁴cells/ml.The growth of chlorella sp.was not significantly affected by iron concentration,and the growth was slightly better in the range of 0.6～1.2mg/L,with the maximum cell density of 6.8×10⁶ cells/ml.The best growth was found in the Fe 2.4mg/L group,with a cell concentration of 8.4×10⁵cells/m L.Scrippsiella trochoidea had the best growth in Fe 0.4mg/L group,with a cell density of 1.0×10⁶ cells/ml.The nutrient elements in the culture medium decreased with time,and the consumption of the target element increased with the increase of the initial added concentration.When the added concentration is lower than the optimal concentration,the algal biomass is proportional to the nutrient consumption;when the added concentration is higher than the optimal concentration,the higher the concentration is,the higher the absorption and assimilation rate of the unit algal cells is.In addition,N,P,Si and Fe were also the limiting factors affecting the content of algal oil.The chloroform-methanol extraction method was used to determine the oil content of algae growing at different concentrations.The results showed that the restriction of N and P could significantly promote the oil content of the four kinds of algae,but the addition of N and P could improve the oil yield of algae due to the influence of biomass.Fe in a certain concentration range can promote the increase of algal oil content and oil yield.Si can promote the oil yield of diatoms,and has no great influence on spirulina,chlorella and Schistosellae.Based on the research results of this paper and previous understandings,this paper provides an experimental basis for volcanic materials to promote the accumulation of organic matter in organic oil.Elements such as N,P,Si and Fe brought by thermal fluid activity and volcanic action in geological period play an important role in the flourishing of microorganisms.In the early stage of volcanic ash falling or hot fluid upwelling,the nutrient elements released by volcanic ash promote the growth of marine organisms,especially the bloom of algae.After that,the nutrient concentration in seawater recovers to the original level,and the oil content of algal bodies starts to accumulate in large quantities under the condition of nitrogen deficiency,phosphorus deficiency and silicon limitation.The biomass and oil yield of algae were significantly increased,which laid a material foundation for the generation of hydrocarbon into oil from the parent material.Therefore,high-quality source rocks may develop during the volcanic-hydrothermal period（stage）.