The Impacts Of Leaked Carbon Dioxide From Underground On Soil—plants System

Currently, geological carbon sequestration is recognized as one of the effective measures to rapidly decrease the level of atmospheric CO₂ in a short term. However, the supercritical CO₂ that are storaged in the underground could be affected by various factors, leading to the CO₂ leakage. This will have a great threat to the ecological environment of the nearby storage sites and even a larger region. Especially, since the soil is a main medium to exchange the matters and energy, the quality of its physical and chemical properties can directly indicate the merits of the groundwater’s quality, microbial diversity and the growth traits of the surface plants etc. Therefore, it is very essential to explore the influence of the leakage of CO₂ on soil properties. This experimental study aimed to explore the reflection on the changes of soil’s chemical parameters that are related to the soil feitility and part of physical properties, then analyze the effects of soil—plants system after different concentrations of CO₂ deliberate invasion. The results have some certain reference to further study the changes of the soil’ environment after the high concentrations of the leakage of CO₂, This may be useful to provide a theoretical basis and practical support for the safety of geological CO₂ storage.The experiment artificially simulated the leakage of CO₂ from the underground via the preset concentrations of CO₂ being continuously injected from the bottom of the testing area of greenhouse and underground’ barrels. Monitoring of the changes in soil pH, total organic carbon, nitrogen, phosphorus, potassium, water-soluble salts and the growth traits of plants were then conducted. In another trial, simulating the extraordinary pressure of CO₂ leakage to the impermeable layer of clay was carried out and monitoring the changes of clay’s temperature, moisture content, negative pressure, pH was then conducted. The main conclusions derived from these trials are obtained as follows:（1） When the concentrations of CO₂ leakage are, respectively, 2%, 4%, and 8%, the pH of the test area of the greenhouse shows a continuous increase with the increase of CO₂. The maximum is about 9.34. Unlike the pH, Ca2+, Mg2+ is decreased with the increased CO₂. Compared with the control, the organic carbon in the soil that croped the soybean, radish, wheat and pea, respectively, was ascended by 1.56%-43.75%. Nutrients, like nitrogen, phosphorus and potassium, are declined. In the soils that croped the radish and pea, the total nitrogen near the rhizosphere was, respectively, reduced by 11.98% and 10.25% in the case of 8% CO₂ injection. Similarly, in the soil near the rhizosphere of wheat and pea, the nitrate was reduced by 94.65% and 76.68%, respectively, in 8% CO₂ injection. Total phosphorus, available phosphorus, total potassium and available potassium show a downward trend with the increasing concentration of CO₂. However, the growth of radish and pea seemed promoted under this concentration of CO₂ injection.（2） When the concentrations of CO₂ leakage are, respectively, 5%, 10%, and 15%, the pH of the soil in the greenhouse was increaded with the increase of CO₂, reaching the maximum of 9.11, while Ca2+ showed a significant decline. Compared with the control, total organic carbon under 5% and 15% conditions was reduced by 10.38% and 16.51%, respectively. With regard to the soil nutrients, total nitrogen, nitrate in the 15% condition are reduced by 17.5% and 87.01%, respectively, while the available phosphorus and potassium in 5% condition are significantly decreased by 15.18%, 16.06%. Total phosphorus and potassium also have a slight increase under the high concentrations of CO₂ invasion. Under this concentration range, the leaf number of pea and ryegrass is decreased and the leaves turned to yellow.（3） When 5%, 10%, 15% concentrations of CO₂ was injected to the outdoor underground’ barrel for 2 years, the soil’s total organic carbon, levels of nitrogen, phosphorus and potassium are all showed the same trends. The content in the upper layer of the barrel was significantly higher than the bottom layer’s regardless the concentration of CO₂. The pH seemed no obvious change in height. With the increase of CO₂, total nitrogen has a slight reduction at the top and bottom of the barrel while available potassium has a minimum value in the case of 10% CO₂ injection. Available phosphorus is declined at the bottom of the barrel. Under the testing CO₂ concentration, plants that croped in the vadose zone of the barrel was responded, the yellow leaf of the corn is gradually increased while the height of wheat is declined.（4） After the extraordinary pressure of CO₂ was invaded to the clay, temperature in different heights appeared no clearly change and moisture content was declined. While the negative pressure is obviously increased, p H is ascended.