Modelling DOC production, transport and retention in forest soils, exploiting recent 14C enrichment at Oak Ridge, USA

植物凋落物中的碳融入森林土壤，以及它在不同土层（土层）中停留的时间，是全球碳循环的重要因素，因此也是气候变化的速度和程度的重要因素。在许多土壤中，溶解有机碳（DOC）在蒸发水中的向下运动是碳转移到深层土壤的主要方式，在那里可以发生长期的碳储存。此外，DOC是土壤中金属、营养盐和有机污染物的重要转运体，也是从土壤到水体的重要转运体。DyDOC是一个基于过程的模型，旨在模拟土壤碳循环，包括DOC的生成和传输。该项目的目的是通过校准一个独特的数据集，正在收集的大气CO2的局部富集，因此森林植被，由于释放的碳-14从焚化炉靠近美国田纳西州的橡树岭保留地，以改善模型。数据收集是由美国同事在一个名为EBIS（富集背景同位素研究）的项目中进行的。碳-14是一种天然放射性同位素，以其在“碳定年”中的应用而闻名，用于年龄在100到数万年之间的样品。然而，它可以用于生态系统研究碳循环的第二种方式是通过人类活动富集大气中的CO2。直到最近，这只是指“炸弹碳”，即20世纪中期大气层武器试验造成的浓缩，大约使全球14 C水平翻了一番。“炸弹标记”的碳可以在不同的土壤池中追踪，通过使用适当的模型，可以推断出其结合和损失的速度。这已用于在欧洲的研究中心校准DyDOC。但现在，1999年橡树岭焚化炉排放的碳-14产生了进一步的本地化标签，由于当地科学家迅速采取行动，在EBIS中建立了监测计划和实验研究，因此可以获得更详细的同位素数据用于建模。这里提出的工作是利用EBIS数据来校准DyDOC更广泛，更精确地比否则是可能的。该项目的工作将首先包括整理EBIS关于土壤碳14 C的数据、不同土壤池中的碳量和DOC浓度，以及其他表征橡树岭森林的当地数据（土壤深度、降雨量、温度、凋落物等）。然后，我们将运行模型，调整其参数，以尽可能接近测量值。将进行额外的模型运行，以查看输出对参数值变化的敏感程度。校准后的模型将用于预测（a）土壤碳库和DOC的碳-14标记的演变，为将来收集更多数据做好进一步测试的准备，以及（B）土壤碳循环和DOC形成和运输对外部环境因素（如温度，降雨量和凋落物输入）的依赖性。研究结果应提供有用的资料，以评估森林土壤对未来气候和其他环境条件变化的可能反应。这种“一次性”的应用程序的模型，一个独特的研究网站将提供的信息，可以用来限制的范围内的参数值允许在模型应用到其他网站，因此，最终更可靠的区域尺度的森林土壤碳行为的预测。

The incorporation of the carbon of plant litter into forest soils, and how long it spends in different soil layers (horizons), are important factors in the global carbon cycle, and therefore in the rate and extent of climate change. In many soils, downward movement of dissolved organic carbon (DOC) in percolating water is the main means by which carbon is transferred to deeper soil layers, where long-term carbon storage can occur. Moreover, DOC is an important transporter of metals, nutrients and organic contaminants in soils, and from soils to water. DyDOC is a process-based model designed to simulate the soil carbon cycle, including DOC generation and transport. This project aims to improve the model by calibrating it on a unique data set that is being collected following the localised enrichment of atmospheric CO2, and hence forest vegetation, due to the release of carbon-14 from an incinerator close to the Oak Ridge Reservation in Tennessee USA. The data collection is being carried out by American colleagues in a project called EBIS (Enriched Background Isotope Study). Carbon-14 is a natural radioactive isotope, well-known for its application in 'carbon dating', for samples of ages in the range 100 to tens of thousands of years. However, a second way in which it can be used in ecosystem research into the carbon cycle is through the enrichment of atmospheric CO2 by human activities. Until recently, this only meant 'bomb carbon', enrichment caused by atmospheric weapons testing in the middle of the 20th Century, which approximately doubled the worldwide 14C level. The 'bomb-labelled' carbon can be traced in different soil pools and, through the use of an appropriate model, its rate of incorporation and loss can be deduced. This has already been used to calibrate DyDOC at sites in Europe. But now a further localised label has been generated by the emission of carbon-14 from the incinerator at Oak Ridge during 1999, and, thanks to the swift actions of local scientists in setting up a monitoring programme and experimental studies in EBIS, much more detailed isotope data are consequently available for modelling. The work proposed here is to make use of the EBIS data to calibrate DyDOC much more extensively and precisely than would otherwise be possible. The work in the project will firstly comprise the collation of the EBIS data on soil carbon 14C, the amounts of carbon in different soil pools, and DOC concentrations, together with other local data (soil depths, rainfall, temperature, litterfall etc) characterising the Oak Ridge forests. We will then run the model, adjusting its parameters in order to match as closely as possible the measured values. Additional model runs will be done to see how sensitive the outputs are to changes in the parameter values. The calibrated model will be used to forecast (a) the evolution of the carbon-14 labelling of soil carbon pools and DOC, in readiness for further testing as more data are collected in the future, and (b) the dependence of soil carbon cycling and DOC formation and transport on external environmental factors such as temperature, rainfall and litter inputs. The results should provide useful information to assess the possible responses of forest soils to future variations in climate and other environmental conditions. This 'one-off' application of the model to a unique research site will provide information that can be used to limit the ranges of parameter values permissible in model applications to other sites, and therefore ultimately to more reliable regional-scale forecasting of forest soil carbon behaviour.