季节性冻结地区小流域水、碳、氮循环相互作用过程模型研究

Global warming and human activities have been significantly threatening the sustainability of terrestrial ecosystems, which result in decreasing productivity, increasing emissions of greenhouse gases and gaseous air pollutants and, overload of water pollutants. The CNMM-DNDC is a process-oriented model, which aims at simulating water, carbon and nitrogen cycling processes and their interaction at catchment scale. It has been validated with simultaneous observations of multiple variables of water runoff and emissions and leaching of carbon and nitrogen in a subtropical agro-forest with uplands and lowlands for production of crops and forests. In this study, we are to modify CNMM-DNDC by incorporating the scientific processes of the Northern Ecosystem Soil Temperature (NEST) model and parameterizing the biogeochemical effects of grazing into it. Our goal is to build the model’s capacity of simulating the coupled water, carbon and nitrogen cycling processes in catchments of seasonal frozen region. Then, the modified CNMM-DNDC will be tested, verified and validated against simultaneous observations in the seasonal frozen alpine ecosystems in a typical catchment of the Qinghai-Tibetan Plateau. It’s applicability will be investigated by analyzing the effects of grazing intensity on water runoff, emissions of carbon and nitrogen gases, hydrological losses of dissolved carbon and nitrogen and net primary productivity of the ecosystems. This update of the model is expected to not only provide a model tool for studying the responses of regions with seasonal frozen soil to global change and management practices, but also to broaden the model applicability.

气候变化和人类活动的双重影响严重威胁陆地生态系统功能的可持续性，使其同时出现生产力下降，碳氮温室气体和大气污染气体排放增强，以及水体碳氮污染物负荷过重等生态环境问题。动力学模型CNMM-DNDC旨在实现对流域水、碳、氮迁移转化及其相互作用的分布式长周期模拟，对亚热带小流域的模拟结果已经通过了综合观测数据的检验。本项目拟引入高寒土壤热量模型的科学过程，建立放牧影响生物地球化学过程的参数化方案，从而实现该模型模拟季节性冻结地区小流域水、碳、氮循环相互作用的能力，以解决当前模型版本在季节性冻结地区尚不适用的问题，利用青藏高原日尔郎小流域丰富的野外周年同步综合观测数据检验改进模型的模拟能力，且通过分析研究不同放牧强度情景下模型对上述小流域水、碳、氮循环过程的综合模拟结果，进一步评估和提升模型在季节性冻结地区流域生态系统水、碳、氮调控研究中的适用性。

构建适用于不同气候带的水碳氮动力学模型可以通过模拟试验定量流域生态系统水碳氮迁移和转化过程的关键物质浓度和通量，为制定和采取有效的调控措施，维护流域生态系统安全和可持续性提供科学依据。因此，本项目通过耦合高寒冻土模块进一步扩展水碳氮耦合模型CNMM-DNDC的适用性，实现其对于高寒冻土区（季节性和多年冻土）水碳氮过程的模拟。耦合的高寒冻土模块不仅实现模型对于高寒地区土壤冻融及雪层动态等过程的模拟，同时也能够有效的再现其对于亚热带地区土壤温度的模拟能力，说明耦合模块对于土壤水热过程模拟的有效性和普适性。新版本模型在日尔郎山流域的模拟测试表明，模型能够有效把握季节性冻融地区碳氮循环过程的基本特征，包括高寒草甸和林地的CH4吸收、N2O和NO排放日通量以及高寒湿地CH4排放日通量，野外观测和模型模拟共同表明季节性冻土地区碳氮周转速率较低。此外，基于情景分析，初步探讨放牧强度对高寒草甸净温室气体排放的影响。因此，本项目研究进一步扩展了模型的适用性，有效的促进其推广应用和虚拟试验研究的开展。