Investigating the potential of enhanced weathering as a carbon dioxide removal technique using a range of materials applied to agricultural soil

使用一系列应用于农业土壤的材料来研究增强风化作为二氧化碳去除技术的潜力

• 批准号: 1928849
• 金额: --
• 依托单位: University of Oxford
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-1928849
• 关键词: Investigating; potential; enhanced; weathering; carbon

Weathering of silicate minerals is a natural method of carbon sequestration; helping to regulate the global C cycle and atmospheric CO2 on geological timescales. The application of silicate minerals to agricultural soils has been suggested as a method to enhance natural silicate weathering rates and increase C drawdown; thereby reducing atmospheric pCO2. The potential for "enhanced weathering" succeeding as a CO2 removal technique is poorly understood due to conflicting estimates for mineral dissolution rate. Laboratory studies estimate dissolution rates to be an order of magnitude faster than field studies and do not consider the effect of mineral addition. Whilst field studies capture the complex array of processes interacting within the soil zone, the experiments are consuming in both time and space, and so by their nature are limited. Further to this, it is difficult to isolate and assess the effect of individual processes occurring during a field study; a problem when trying to apply the findings to different locations. Soil core experiments address the limitations of laboratory and field studies, allow more experiments to run and act as a powerful compliment to field studies. In this study, soil cores will be taken from an agricultural site and monitored in a controlled laboratory environment. This will allow dissolution rates to be assessed whilst maintaining the complexity of the soil zone. To date, only a few studies have used soil core experiments to investigate the impact of silicate supply on dissolution rates. Soil core flow through experiments by Renforth et al, 2015, suggest that the experimental method described above can provide useful insights into dissolution rate. This study aims to extensively expand this early research using multiple soil cores from the same agricultural site. Different silicate minerals (olivine, wollastonite, K-feldspar, basalt, volcanic ash) will be added to each of the cores. Core experiments will be run in triplicate with a triplicate-control to assess natural variability and the chemical impact of each type of mineral addition. The soil cores will be subjected to realistic UK weather conditions for 6 months by placing them on the roof of the Earth Sciences Department, Oxford. The effect of temperature and rainfall supply on dissolution rate will be assessed by replicating the experiment in a temperature controlled laboratory. Changes in the cation concentration within weekly samples of dripwater will allow comparisons to be made between the dissolution rates of different silicates minerals. The application of enhanced weathering as a C sequestration strategy is further limited by our incomplete understanding of the pathway C follows during the weathering process. To understand the effect of enhanced weathering on C uptake, it is important to identify the extent that C remains in the soil zone, following precipitation as a pedogenic carbonate; or whether the C remains in solution, entering the freshwater and marine ecosystem as bicarbonate ions, and thus increasing ocean alkalinity. To investigate the uptake of C after the application of different silicate minerals to agricultural soil, the carbonate chemistry of the soil core will be examined before and after the experiment; and the bicarbonate concentration of dripwater leaving the soil cores will be measured at regular intervals throughout the 6-month experiment. One concern which could limit the application of enhanced weathering as a large scale CO2 removal technique is the impact increasing silicate supply has on the production of trace metals that are harmful to primary productivity and affect freshwater and ocean chemistry. However, the production of these trace metals and their resultant pathway through the terrestrial, river and marine ecosystem remains uncertain.

硅酸盐矿物的风化是碳固存的一种自然方法；有助于在地质时间尺度上调节全球碳循环和大气二氧化碳。硅酸盐矿物在农业土壤中的应用被认为是一种提高自然硅酸盐风化速率和增加碳排放的方法，从而减少大气中的二氧化碳。由于对矿物溶解速率的不同估计，人们对“强化风化”作为一种二氧化碳去除技术的成功潜力知之甚少。实验室研究估计溶解速度比实地研究快一个数量级，不考虑矿物添加的影响。虽然实地研究捕捉到了土壤带内相互作用的复杂过程，但实验既耗费时间又耗费空间，因此它们的性质是有限的。此外，很难隔离和评估实地研究期间发生的个别过程的影响；当试图将发现应用于不同地点时，这是一个问题。土壤岩心实验解决了实验室和实地研究的局限性，允许进行更多的实验，并作为实地研究的有力补充。在这项研究中，土壤岩心将从一个农业场地提取，并在受控的实验室环境中进行监测。这将允许在保持土壤区的复杂性的同时评估溶解速率。到目前为止，只有少数研究使用土芯实验来调查硅酸盐供应对溶解速度的影响。Renforth等人2015年的实验表明，上述实验方法可以为溶解速率提供有用的见解。这项研究的目的是利用同一农业场地的多个土芯来广泛扩展这一早期研究。不同的硅酸盐矿物(橄榄石、硅灰石、钾长石、玄武岩、火山灰)将被添加到每个岩芯中。核心实验将进行一式三份，并进行三份对照，以评估自然变异性和每种矿物添加的化学影响。通过将土芯放置在牛津地球科学部的屋顶上，这些土芯将在英国现实的天气条件下持续6个月。温度和降雨量对溶出率的影响将通过在温度控制的实验室中重复实验来评估。每周滴水样品中阳离子浓度的变化将使人们能够比较不同硅酸盐矿物的溶解速度。由于我们对风化过程中C途径的不完全理解，加强风化作为碳封存策略的应用受到进一步的限制。为了了解加强风化对碳吸收的影响，重要的是要确定在降水后，碳作为成壤碳酸盐留在土壤带中的程度；或者碳是否留在溶液中，以重碳酸盐离子的形式进入淡水和海洋生态系统，从而增加海洋碱度。为了研究不同硅酸盐矿物应用于农业土壤后对C的吸收情况，将在试验前后检测土芯的碳酸盐化学，并在整个为期6个月的试验中定期测量滴水离开土芯的碳酸氢盐浓度。一个可能限制作为大规模二氧化碳去除技术的强化风化的应用的担忧是，增加的硅酸盐供应对痕量金属的生产产生影响，这些金属对初级生产力有害，并影响淡水和海洋化学。然而，这些痕量金属的产生及其通过陆地、河流和海洋生态系统的途径仍然不确定。