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

淡水中的硝酸盐污染仍然是一个国际问题，主要来自农业活动。它威胁着英国的环境、经济和人类健康。硝酸盐浓度超过欧盟饮用水标准每升50毫克，许多英国淡水(地下水和地表水)的硝酸盐浓度呈上升趋势。在淡水循环中，从土壤中淋洗的硝酸盐(在土壤氮素转化后，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(B)在到达井眼、泉水和溪流之前缓慢地通过非饱和带(从土层底部到地下水位)和饱和带。地下水和溪水之间的相互作用可能会严重影响彼此的水质，因为它们在地下水位带(位于河床下方并与河床相邻的地带)中相互作用。通过最近的研究，越来越清楚的是，由于硝酸盐的储存及其在非饱和区和饱和区的潜在长时间滞后，从土壤中淋洗的硝酸盐可能需要数十年的时间才能排放到淡水中。然而，在目前的水硝酸盐管理和政策制定中，很少考虑这一时间滞后，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每个单独组成部分中的硝酸盐过程有了比以前更好的了解，但仍然不完整；需要进行进一步的整体研究，以促进我们对相互关联的整个循环中的硝酸盐过程的了解。我建议通过发展一种综合的模拟方法来研究土壤和非饱和、饱和和半湿润带中的硝态氮运移和主要的氮素转化。为了演示目的，将开发一个在线实时建模系统的原型。开发这样一种综合建模方法是一个重大挑战。它以前从未尝试过，其复杂程度涉及土壤、水文学、水文地质学、生物地球化学和景观科学的整合。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有全新的见解，并直接惠及学术社会和水硝酸盐管理政策制定者，从而间接降低因水硝酸盐问题(例如，处理饮用水中硝酸盐的成本，以及与水硝酸盐有关的人类疾病的成本)而产生的经济成本。本研究开发的方法和工具可以移植到其他领域。我在伊甸谷开发了模拟地下水和非饱和区径流、地下水补给和硝酸盐迁移的数值模型，将作为这项研究的试验区。由于它也是NERC常量营养素循环和DEFRA示范测试集水区方案中正在研究的集水区之一，该项目将对这些正在进行的方案作出宝贵贡献。这也意味着有大量的可用数据。实时的概念(如这里所述)并不一定意味着短的建模间隔，而是一种自动建模并立即提供结果和模型的方法。该项目将展示的新的在线和实时建模方法将极大地促进利益攸关方之间以非常经济高效的方式进行有效沟通，并有可能通过实时发布自动更新的在线信息，增加流域社区(包括农民和普通公众)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.