Response Mechanism Of Soil-Vegetation System To High Concentration CO₂ Leakage And Spectral Monitoring Technology

The technology of carbon capture and storage?CCS?is one of the most effective methods to decrease global carbon dioxide emissions.However,the security of carbon dioxide geological storage has been the key point and difficult point of this technology.Once stored carbon dioxide leaks,it enters the atmosphere and soil in the form of gas or soda,which would influence soil biological system,vegetation and change ecosystem balance.In severe cases,it can bring pressure to the survival of human beings and livestock.In this study,the characteristics of soil vegetation system were observed in situ,based on the natural CO₂ leakage field of Sanhe towns in Ping'an District Haidong city Qinghai province,reveal the changes of soil characteristics and soil reflectance,reveal the changes of plant ecophysiological characteristics,establish mathematical model based on responding of soil-plant system and changes of hyper spectral features,put forward the method to detecting leakage of CO₂ during CCS,proposed the monitoring system by combining indexes obtained from high altitude,surface ground,biology and groundwater.The results as follows:?1?CO₂ leakage will significantly affect the atmospheric CO₂ concentration at the point of leakage.CO₂ concentration up to 489476-641 ppm above eruption point at 5cm.At 70 cm high,CO₂ concentration amount to 5010-429 ppm,which concentration has potentially harmful to the surrounding biology However,CO₂ concentration significantly reduced when height higher than 140 cm and the minimum value is consistent with the natural atmospheric carbon dioxide concentration.The results of different directions of CO₂ concentration showed that,wind direction is the main factor affecting the CO₂ concentration.Under the main wind direction,the CO₂ concentration is between 2300-400 ppm and the non-main wind direction is between 1550-400 ppm.The eruption of CO₂ gas was analyzed by carbon isotope technique.The results showed that the carbon isotope values are 0.04±0.36‰,which far below the carbon isotopic composition of CO₂ in the natural atmosphere.Combined with the existing research results,we can conclude that the eruption of CO₂ mainly comes from the earth crust.?2?Affected by erupted spring erupt intermittent CO₂,5 meters range of soil surface covered by flaky calcium layer.The soil is very tight and the soil color is lighter with yellowish brown.In 10 meters range,the impact of intermittent CO₂ eruption weakened.Soil surface layer is a granular cover and soil compactness decreased.Soil color is dark and grayish brown.Changes in soil structure affect soil penetration and retention of water.Generally,Soil moisture content increased and then decreased with depth.However,due to the role of calcium layer barrier,the variation of water content in the soil layers of the near eruption spring was significant,while the water content of the layers of the soil far from the eruption spring is gentler.?3?In a certain range,the higher the water content of the soil,the lower the spectral reflectance;the higher the soil color,the higher the spectral reflectance;the higher degree of coverage of soil,the lower the spectral reflectance.The soil reflectance spectra showed strong absorption peaks at 580 nm and 680 nm under CO₂ stress.Through data conversion of the soil reflectance spectrum and then data differential processing,especially first-order differential method as one of the ideal treatment,significantly enhanced the absorption peak.?4?The reflection spectrum feature analysis for soybean leaf stressed by CO₂ leakage has shown that,the absorption depth,normalized reflection at absorption valley,normalized reflection at green peak,red edge position,red shoulder position,absorption width and degree of symmetry of spectral characteristic parameters for soybean leaf during the mature period have a definite relation with the change of CO₂ leakage stress and have no definite numerical relationship with the absorption valley position and green peak position.?5?By measuring the hyperspectral reflectance and chlorophyll content in soybean and potato leaves under the stress of CO₂ leakage as well as the continuum removal disposal and derivative spectrum calculation for hyperspectral data within the wavelength range of 400⁸00nm,10 spectral feature parameters could be achieved.The correlation analysis of high spectrum and change characteristics of chlorophyll content in soybean and potato leaves based on analysis of physical significance for above parameters is thus conducted.The result has shown that,under the stress of CO₂ leakage,the chlorophyll content of soybean change,absorption valley position,normalized reflectance at the green peak position and red edge position are closely related and in this way,the chlorophyll content equation: Y=-19575+ 11.9X1-45.1X2+17.6X3 is obtained.And that under the CO₂ stress,chlorophyll content of potato correlation to characteristic parameters which is normalized reflectance at max absorption position,red edge,and absorption width.Chlorophyll content retrieval equation is obtained: Y=-2260.315+1769.767X1 +0.068X2+12.366X3.The result of this paper has very important meaning and application values for CO₂ geological storage monitoring and evaluating land-surface ecology under CO₂ stress and monitoring the leakage spots by using remote sensing technique.?6?In order to obtain the best red edge position algorithm,six red edge position extraction methods,which are red edge position maximum first derivative,with Lagrange,with line extrapolate method,with four-point inter,with Gaussian and with polynomial fitting,were compared for soybean and tomato leaf under higher CO₂ stress.The results show that the different algorithms of red edge position are significantly linear correlation with chlorophyll content of soybean and tomato leaf.However,largest first derivative and Lagrange are the optimal extract methods to calculate red edge position for soybean and tomato leaf under CO₂ stress.Moreover,the maximum first derivative method is more simple and stability.The results imply that red edge position changes can reflect plant chlorophyll content and can be used to monitoring CO₂ leakage during CCS project using aboveground plant remote sensing data.?7?Six different methods were used to extract the red edge position of soybean and potato leaves under CO₂ leakage stress.The results showed that the red edge position extract by the maximum first order derivative method and the Lagrangian interpolation method had the highest correlation with the chlorophyll content,while the four-point interpolation has the lowest correlation.However,the red edge position extract by the inverted-Gaussian fitting method and linear four-point interpolation method had the highest correlation with the chlorophyll content,while the polynomial fitting method has the lowest correlation.?8?Established a safety monitoring system for carbon dioxide geological storage by integrated remote sensing-vegetation-soil-groundwater data.For carbon capture storage,from multi-scale,multi-angle to ensure security storage,we combined multiple indicators,and the most important indexes are surface displacement characteristics,soil and vegetation spectral changes,changes of physiological and ecological characteristics of vegetation,soil microbiological,animal and physical and chemical properties and chemical characteristics of groundwater.