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

利用美国橡树岭最近的 14C 富集对森林土壤中 DOC 的产生、运输和保留进行建模

• 批准号: NE/D00697X/1
• 负责人: Edward Tipping
• 金额: $ 5.1万
• 依托单位: NERC CEH (Up to 30.11.2019)
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FD00697X%2F1
• 关键词: Modelling; DOC; production; transport; retention

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.

植物凋落物的碳与森林土壤的结合，以及它在不同土层（层）中停留的时间，是全球碳循环的重要因素，因此也是影响气候变化速度和程度的重要因素。在许多土壤中，渗透水中溶解有机碳（DOC）的向下运动是碳转移到深层土壤的主要手段，在那里可以发生长期的碳储存。此外，DOC是金属、养分和有机污染物在土壤中以及从土壤到水的重要转运体。DyDOC是一个基于过程的模型，旨在模拟土壤碳循环，包括DOC的产生和运输。这个项目的目的是通过校准一个独特的数据集来改进模型，该数据集是在美国田纳西州橡树岭保护区附近的一个焚化炉释放碳-14导致大气中二氧化碳和森林植被局部富集后收集的。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是一种天然的放射性同位素，以其在“碳定年”中的应用而闻名，用于测定年龄在100年至数万年之间的样品。然而，第二种将其用于生态系统碳循环研究的方法是通过人类活动对大气二氧化碳的富集。直到最近，这只意味着“核弹碳”，即20世纪中叶大气武器试验造成的浓缩，使全球碳浓度增加了大约一倍。“炸弹标记”的碳可以在不同的土壤库中被追踪到，并且通过使用适当的模型，可以推断出它的掺入率和损失率。这已经被用于校准DyDOC在欧洲的站点。但是现在，由于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，并且由于当地科学家在建立监测计划和EBIS实验研究方面的迅速行动，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数据比其他方法更广泛和更精确地校准DyDOC。该项目的工作将首先包括整理EBIS关于土壤碳14C的数据，不同土壤池中的碳量，DOC浓度，以及其他描述橡树岭森林特征的当地数据（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的变化有多敏感。校正后的模型将用于预测(a)土壤碳库和DOC的碳-14标记的演变，为未来收集更多数据的进一步测试做好准备；(b)土壤碳循环和DOC形成和运输对外部环境因素（如温度、降雨和凋落物输入）的依赖。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。这种将模型“一次性”应用于一个独特的研究地点将提供信息，可用于限制模型应用于其他地点时允许的参数值范围，从而最终实现更可靠的森林土壤碳行为区域尺度预测。