Implications of groundwater-surface water connectivity for nitrogen transformations in the hyporheic zone

地下水-地表水连通性对潜流带氮转化的影响

基本信息

批准号：
NE/F006063/1
负责人：
Ann Louise Heathwaite
金额：
$ 49.05万
依托单位：
Lancaster University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FF006063%2F1
关键词：
Implications groundwater surface water connectivity

项目摘要

Rivers have (rather controversially) been described as 'simply outcrops of groundwater'. Many of the rivers in the UK are supplied mainly from groundwater sources, especially during the summer months when rainfall is characteristically low. The hyporheic zone is a critical interface between surface and subsurface waters in groundwater catchments. Here, the mixing of groundwater and surface water and the resulting biological and chemical reactions, may exert a lot of control on the water quality of the river and also its ecology: so much so that the hyporheic zone has been ascribed pollutant attenuating properties by some. Groundwater abstraction, effluent disposal and diffuse nutrient pressures - especially nitrogen - may all compromise the capacity of the hyporheic zone to influence the water quality of a river. Although quite a few researchers have recognised that the hyporheic zone has some special control on the river habitat, most have looked at it only from the perspective of the relationship between river water and the upper few centimetres of the sediments of the riverbed. They have ignored the fact that as well as downward flux from the river into the sediments of the riverbed there will also be upward flows from groundwater through the hyporheic zone and into the river. We are especially interested in what happens to the chemistry of groundwater as it moves through the hyporheic zone. We will look in detail at the relationship between different nitrogen species, such as nitrate and ammonium and chemical reactions known collectively as 'redox' or reduction-oxidation reactions. Redox reactions use electron acceptors other than oxygen for organic carbon oxidation as the amount of oxygen in the riverbed sediments is exhausted. These reactions and their relationship with nitrogen are important because the hyporheic zone has been proposed as a zone in which nitrogen attenuation occurs. This has led to the proposition that the movement of groundwater through this zone will reduce the concentration of nitrogen reaching the river water. In this project, we will investigate further the claim that the hyporheic zone can attenuate groundwater contaminants such as nitrate. We want to look much more carefully at the pattern of flow from groundwater through the hyporheic zone. We propose that groundwater flux is influenced by the permeability of the river bed and this is in turn influenced by the physical structure and topography of the riverbed. We believe that where the permeability of the riverbed is high and flux from groundwater towards the river is high, we will find different patterns of biogeochemical activity in the hyporheic zone compared to where the permeability is low. We like to think of the riverbed rather like a cheese grater with fast and slow flow pathways corresponding to 'holes' in the riverbed. We expect these holes to be quite dynamic as winter storms change the superficial topography of the riverbed sediments and rearrange the patterns of pool-riffle and fast-slow flow features in the underlying sediments of a river. The reason why these flow pathways are important is they may allow 'hotspots' of biogeochemical activity within the hyporheic zone that could be important controls on the ecology of groundwater-fed rivers because they either release or transform nitrogen through processes such as nitrification or denitrification. The latter converts nitrate, which can damage the ecology of a river where it is present at high concentrations, into nitrogen gas, which is harmless. If we are able to show clearly how important the hyporheic zone is in influencing the water quality in rivers that are groundwater-fed, we will be able to provide evidence that can be used to protect this zone, and can also be used in helping the UK meet the requirements of critical European legislation such as the Water Framework Directive.

河流（相当有争议）被描述为“地下水露头”。英国的许多河流主要来自地下水，尤其是在夏季降雨特征很低的情况下。低潮区是地下水集水区的表面和地下水之间的关键接口。在这里，地下水和地表水以及所得的生物学和化学反应的混合可能会对河流的水质及其生态产生很多控制：如此之多，以至于某些人已经归因于污染物衰减特性。地下水抽象，废水处置和弥漫性营养压力 - 尤其是氮气 - 可能都会损害低位区域影响河水质量的能力。尽管相当多的研究人员已经意识到，低音区域对河流栖息地有一些特殊的控制，但大多数人仅从河水与河床沉积物上几厘米的上几厘米之间的关系的角度来看。他们忽略了这样一个事实，即从河流到河床的沉积物的向下通量也将从地下水从地下水到垂下的垂直地区到河流。我们对地下水的化学经历的化学经历在低音区域移动时尤其感兴趣。我们将详细介绍不同氮种之间的关系，例如硝酸盐和铵以及统称为“氧化还原”或还原氧化反应的化学反应。氧化还原反应使用氧气以外的电子受体进行有机碳氧化，因为河床沉积物中的氧气量被耗尽。这些反应及其与氮的关系很重要，因为已经提出了低螺旋区作为发生氮衰减的区域。这导致了这样一个主张，即地下水通过该区域的运动将减少到达河水的氮浓度。在这个项目中，我们将进一步调查低孔区可以减轻硝酸盐等地下水污染物的说法。我们希望更加仔细地研究从地下水到垂直区域的流动方式。我们建议地下水通量受河床的渗透性的影响，而这反过来又受河床的物理结构和地形的影响。我们认为，在河床的渗透性高且从地下水向河流的通量很高，我们将发现低渗透性区域的生物地球化学活动的不同模式与渗透率低相比。我们喜欢想像河床，就像奶酪刨丝器一样，流动速度快，流道与河床中的“孔”相对应。我们预计，随着冬季风暴改变河床沉积物的浅色地形，并重新排列河床的图案和快速慢的流动的图案，我们希望这些孔具有动态性。这些流动路径很重要的原因是它们可能允许在低蠕虫区域内的生物地球化学活动的“热点”，这可能是对地下水喂养河流生态学的重要控制，因为它们要么通过硝化或硝化方法释放或转化氮。后者将硝酸盐转化为硝酸盐，该硝酸盐会损害以高浓度的河流的生态学，即无害的氮气。如果我们能够清楚地展示低多个区域在影响地下水喂养的河流的水质方面的重要性，那么我们将能够提供可用于保护该区域的证据，并且还可以用于帮助英国满足关键欧洲立法的要求，例如《水框架指令》。