Analysis and online real-time integrated modelling of nitrate processes in the whole freshwater cycle

淡水中的硝酸盐污染，主要来自农业活动，仍然是一个国际问题。它威胁着英国的环境、经济和人类健康。硝酸盐浓度超过50毫克NO3每升欧盟饮用水标准，并在许多英国淡水（地下水和地表水）上升趋势。在淡水循环中，从土壤中淋出的硝酸盐（经过土壤氮(N)的转化，如硝化、反硝化和植物吸收）可以(a)快速排放到地表溪流中，或者(b)缓慢地通过非饱和带（从土层底部到地下水位）和饱和带运输，然后到达钻孔、泉水和溪流。地下水和河流的水可能通过在潜流带（河床以下和邻近的区域）中相互作用而严重影响彼此的水质。通过最近的研究，越来越清楚的是，由于硝酸盐的储存和硝酸盐在非饱和区和饱和区潜在的长时间滞后，土壤中浸出的硝酸盐可能需要几十年才能排放到淡水中。然而，在目前的硝酸盐水管理和政策制定中很少考虑到这种时间滞后，尽管由于环境和立法压力迫切需要这样做。虽然我们现在对淡水循环中每个单独组成部分的硝酸盐过程比以前有了更好的了解，但仍然不完整；需要进一步的整体研究来推进我们对相互关联的整个循环中硝酸盐过程的认识。我建议通过开发一种综合建模方法来研究硝酸盐在土壤和非饱和、饱和和潜流带中的迁移和主要N的转化。一个在线和实时建模系统的原型将被开发用于演示目的。开发这样一种综合建模方法是一项重大挑战。以前从未尝试过如此复杂的方法，涉及土壤、水文学、水文地质学、生物地球化学和景观科学的综合。然而，值得追求的是对硝酸盐在相互关联的整个淡水循环中的行为的全新见解，以及对学术界和硝酸盐水管理政策制定者的直接利益，从而间接降低由于硝酸盐水问题造成的经济成本（例如处理饮用水中硝酸盐的成本，以及硝酸盐水相关人类疾病的成本）。在本研究中开发的方法和工具可以转移到其他领域。我在伊甸谷开发了模拟径流、地下水补给、地下水和非饱和带硝酸盐运移的数值模型，将作为本研究的试验区。由于它也是NERC宏观营养循环和DEFRA示范测试集水区计划正在研究的集水区之一，该项目将对这些正在进行的计划作出宝贵的贡献。这也意味着有大量的可用数据。实时的概念（如这里所描述的）并不一定意味着一个短的建模间隔，而是一种自动建模和立即交付结果和模型的方法。在这个项目中展示的新颖的在线和实时建模方法将以一种非常具有成本效益的方式极大地促进利益相关者之间的有效沟通，并有可能通过发布实时自动更新的在线信息，增加集水区社区（包括农民和公众）对硝酸盐管理政策制定的参与。

Nitrate pollution in freshwater, which is mainly from agricultural activities, remains an international problem. It threatens environment, economics and human health in the UK. Nitrate concentrations are more than 50 mg NO3 per liter EU drinking water standard with a rising trend in many UK freshwaters (groundwater and surface water). In the freshwater cycle, nitrate leached from the soil (after soil nitrogen (N) transformations, such as nitrification, denitrification and plant uptake) can (a) quickly discharge into surface streams, or (b) slowly transport through the unsaturated zone (from the base of the soil layer to water table) and the saturated zone before reaching boreholes, springs and streams. Groundwater and stream water may heavily influence each other's qualities through the interactions between them in the hyporheic zone (a zone below and adjacent to a streambed). Through recent research, it has become increasingly clear that it could take decades for leached nitrate from the soil to discharge into freshwaters due to nitrate storage and its potentially long time lag in the unsaturated and saturated zones. However, this time lag is rarely considered in current water nitrate management and policy development, although there is an urgent need to do so because of environmental and legislative pressures. While we now have a much better, although still incomplete, understanding of nitrate processes in each separate component of the freshwater cycle than before; further holistic research is required to advance our knowledge of nitrate processes in the interconnected whole cycle. I propose to investigate the nitrate transport and major N transformations in the soil and in the unsaturated, saturated and hyporheic zones by developing an integrated modelling method. A prototype of online and real-time modelling system will be developed for demonstration purposes. The development of such an integrated modelling method is a major challenge. It has never been tried before with such level of complexity involving the integration of soil, hydrology, hydrogeology, biogeochemistry and landscape sciences. However, it is worth pursuing with the reward of entirely novel insights into the behaviour of nitrate in the interconnected whole freshwater cycle, and direct benefit to academic society and water nitrate management policy makers, thus indirectly reducing the economic costs due to water nitrate problems (e.g. costs of treating nitrate in drinking water, and water nitrate related human diseases). The methods and tools developed in this research can be transferable to other areas. The Eden Valley, where I have developed numerical models in simulating runoff, groundwater recharge, and nitrate transport in groundwater and in the unsaturated zone, will be used as a testing area in this study. As it is also one of the catchments being studied in the NERC Macronutrient Cycles, and DEFRA Demonstration Test Catchment programmes, this project will be a valuable contribution to these ongoing programmes. This also means that there is a large amount of available data. The concept of real-time (as described here) does not necessarily imply a short modelling interval, but rather a way for automatically modelling and immediately delivering results and models. The novel online and real-time modelling method to be demonstrated in this project will greatly facilitate the efficient communication between stakeholders in a very cost-effective way, and have a potential to increase the participation of the catchment's community (including farmers and the general public) in nitrate management policy development, by publishing online information updated automatically in real-time.