Simulation Experiment Research Of The Impact Of CO₂Leakage From Geological Storage On Maize And Alfalfa

Carbon Capture and Storage （CCS） is considered an emerging technology that potentially reducesemission massively, which was explicitly listed as one of the major practices for future global carbonreduction together with CDM （Clean Development Mechanism） at the Durban Conference on ClimateChange （South Africa, December2011）. However, there is a risk of leakage with CCS projects. In theevent of leakage, the contribution by CCS to climate change mitigation would be discounted, andecology environment might be noticeably disrupted. Therefore, a quantitative assessment of impacts byleaked geologically stored CO₂on plants to determine their tolerable thresholds and find out theprinciples and processes is of great importance to the assessment of CCS risks, development of emissionreduction policies, guidance to public awareness as well as monitoring and avoidance of any accidentalleakage in the production practice.In order to understand what impacts such leakage might be brought about to maize and alfalfa interms of growth and development and soil, a particular study was made, in which a platform wererestructured to simulate the stored and leaked CO₂. In the initial stage of growth, pure CO₂gas wascontinuously injected into the root zones of maize in seven different fluxes between0and8000g/（m²·d）and alfalfa in five different fluxes between0and2000g/（m²·d）. The changes of several importantparameters of maize and alfalfa were observed and recorded so as to evaluate impacts of undergroundstored CO₂leaking on the two plants, and then to establish the tolerable threshold value. The mainconclusions are as follows:1. Maize and alfalfa were adversely affected by geologically stored CO₂leaking at lower rootzones over fluxes of500g/（m²·d）. Seedling of maize was severely hampered. The two plants wereinhibited in height. The leaf number and area of maize decreased. The photosynthesis of maize wassubstantially hindered. The dry matter of the two plants accumulated above and below ground dropssignificantly. In general, maize and alfalfa grew worse and were inhibited significantly earlier whenCO₂leaking flux increased.2. The soil of maize and alfalfa were also adversely affected by geologically stored CO₂leaking.The soil acidified. The O₂concentration at a soil layer of10-20cm and30-40cm below the maize andalfalfa fields dropped. Moreover, the relationship between the soil O₂concentration and the CO₂injection flux was expressed reliably as a linear equation. The fluxes of CO₂, CH₄and N₂O all showed alinear tendency to rise when CO₂leaking flux increased. The impact on soil became serious when CO₂leaking flux increased.3. When sequestrated CO₂leaked, the dicotyledonous alfalfa was more affected than themonocotyledonous maize due to the fact that the former was more sensitive and less tolerant than thelatter. Accordingly, it may be recommended that farmers in sequestration sites choose to grow monocotsas far as possible in order to reduce effects of stored CO₂leaking.4. When the flux of leaked CO₂meeted500g/（m²·d）, the two plants were not noticeably affected in growth and development. When it meeted2000g/（m²·d）, they approached zero （0） in all theirphysiological indexes quickly. When it meeted a interval of500-2000g/（m²·d）, the two plants wereinhibited significantly or very significantly, that is, the flux of500g/（m²·d） might be the threshold formaize and alfalfa to tolerate leaked CO₂.5. The adverse impacts of leaked CO₂to maize and alfalfa are felt through the replacement of soilCO₂with exogenous O₂and the reduction of O₂concentration at root zones to inhibit root respiration,reducing soil pH and plant energy sources, inhibiting the absorption of root water and mineral nutrients,and impeding leaf photosynthesis.The impact study about CO₂leakage from geological storage on ecological environment is limitedin the world and blank in China. The result of study is still have a certain degree of uncertainty. It ishoped to strengthen research in multi-type crops, soil physicochemical properties, and crop genetics andbreeding so as to obtain a more convincing conclusion.