Nutrient release from coniferous woodland stimulated by changes in forest management: A new nitrate time bomb?

尽管自1970年以来，英国的氮(N)排放量大幅减少，但最近的总氮沉降量没有变化。营养模型表明，英国大多数阔叶树和针叶树系统的氮素负荷超过了临界限值。森林生态系统是高效的大气氮素清道夫，与其他土地利用方式相比可以积累更多的氮素，特别是在林地边缘附近和发生栖息地碎片化的地方。森林研究收集的数据表明，森林土壤中积累了大量的氮和碳(C)，特别是在上层有机土壤中。在一些地点检测到N和C物种的淋溶增加。如果由于森林管理的变化，储存在森林土壤中的氮被矿化和释放，则森林土壤中储存的氮对水质构成风险。全球每年因水处理和富营养化造成的环境破坏造成的水系统氮损失损失高达数十亿英镑。尽管存在这种风险，但人们对森林管理变化对氮从森林向水生系统淋失的潜在影响知之甚少。目前的政府政策建议更多地植树造林，但也要改变更适合未来气候的树种，并将一些针叶树系统转变为本土阔叶树。此外，生产性森林与密集的森林管理过程有关，所有这些过程都会在植树之前、森林发展和收获期间扰乱土壤。病虫害引起的森林变化也可能对森林生态系统的硝酸盐输入和淋失产生深远影响。总而言之，我们期待着森林覆盖的显著变化，这可能会改变我们知之甚少的已建立的N淋失机制，从而产生一个重大的研究需求。PHD将使用监测和建模方法，在一系列尺度上量化进入水生系统的N通量。PHD将通过以下任务实现这一目标：1.对英国10个森林研究监测点测量的土壤和土壤溶液氮(总氮、硝酸盐、氨氮、溶解有机氮)的长期(&gt；15年)监测数据进行详细的定量分析。将进行额外的监测数据收集和实验室分析(土壤氮素淋溶、地下水硝酸盐浓度、孔隙水剖面)。开发概念模型和基于过程的模型，在每个地点将N淋失到水生系统，以及描述森林中N淋失的一些概括性情景，以用于大规模建模。通过利用森林研究中心和CEH的国家尺度数据集，例如生物土壤(220个地点)和土壤调查和水文地质数据，将特定地点的模型扩大到国家规模。应用已开发的模型(现场和国家尺度)来预测森林管理的变化对森林氮通量的影响，以及由此对水生系统氮浓度的影响。

Despite large UK reductions in nitrogen (N) emissions since 1970, recent total N deposition was unchanged. Nutrient models indicate that N loads in most broadleaf and conifer systems in the UK exceed critical limits. Forest ecosystems are efficient atmospheric nitrogen scavengers and can accumulate more nitrogen than other land uses, particularly near woodland edges and where habitat fragmentation has occurred. Data collected by Forest Research suggest that large amounts of nitrogen and carbon (C) have accumulated in forest soils and in particular in the upper organic soil horizons. Increased leaching of N and C species has been detected at a number of sites. Nitrogen stored in forest soils presents a risk to water quality if N stores are mineralized and released as a result of changes in forest management. Nitrogen losses to aquatic systems cost billions of pounds per year globally in water treatment and environmental damage from eutrophication. Despite this risk, the potential impact of changes in forest management on N leaching from forests to aquatic systems is poorly understood. Current government policy proposes more afforestation, but also changes to tree species which are more suitable for future climates, and converting some conifer systems to native broadleaves. In addition, productive forests are associated with intensive forest management processes which all can disturb the soils before tree planting, during forest development and harvest. Changes in forest due to pests and diseases could also have profound impact on nitrate inputs and leaching in forest ecosystems. In summary, we are expecting significant change of forest cover which is likely to alter established N leaching regimes which we know little about, thus creating a major research need.ApproachThis PhD will quantify the impacts of changes in forest management practices on nitrogen fate and transport beneath forested areas in the UK. The PhD will use monitoring and modelling approaches to quantify N fluxes to aquatic systems at a range of scales. The PhD will achieve this through the following tasks:1. Detailed quantitative analysis of long term (>15 years) monitoring data of soil and soil solution nitrogen (total, nitrate, ammonium, dissolved organic nitrogen) measured at 10 Forest Research monitoring sites across the UK. Additional monitoring data collection and lab analysis will be carried out (soil N leaching, groundwater nitrate concentrations, pore water profiles).2. Development of conceptual and process-based models of N leaching to aquatic systems parameterised at each site, and a number of generalised scenarios describing N leaching from forests, to be used in large scale modelling.3. Upscaling of site-specific models to national scale by exploiting national scale datasets from Forest Research and CEH, e.g. BioSoil (220 sites) and soil survey and hydrogeological data.4. Application of developed models (site and national scales) to predict impacts of changes in forest management on N fluxes from forests, and resultant impacts on aquatic system N concentrations.