NERC Centre for Ecology & Hydrology, Maclean Building, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8BB, UK.
Grassland, Soil and Water Research Laboratory, USDA-ARS, Temple, TX 76502, United States.
Sci Total Environ. 2018 Apr 15;621:849-862. doi: 10.1016/j.scitotenv.2017.11.128. Epub 2017 Dec 18.
This study provides a first national-scale assessment of the nutrient status of British headwater streams within the wider river network, by joint analysis of the national Countryside Survey Headwater Stream and Harmonised River Monitoring Scheme datasets. We apply a novel Nutrient Limitation Assessment methodology to explore the extent to which nutrients may potentially limit primary production in headwater streams and rivers, by coupling ternary assessment of nitrogen (N), phosphorus (P), and carbon (C) depletion, with N:P stoichiometry, and threshold P and N concentrations. P limitation was more commonly seen in the rivers, with greater prevalence of N limitation in the headwater streams. High levels of potential P and N co-limitation were found in the headwater streams, especially the Upland-Low-Alkalinity streams. This suggests that managing both P and N inputs may be needed to minimise risks of degradation of these sensitive headwater stream environments. Although localised nutrient impairment of headwater streams can occur, there were markedly lower rates of P and N impairment of headwater streams relative to downstream rivers at the national scale. Nutrient source contributions, relative to hydrological dilution, increased with catchment scale, corresponding with increases in the extent of agricultural and urban land-use. The estimated nutrient reductions needed to achieve compliance with Water Framework Directive standards, and to reach limiting concentrations, were greatest for the Lowland-High-Alkalinity rivers and streams. Preliminary assessments suggest that reducing P concentrations in the Lowland-High-Alkalinity headwater streams, and N concentrations in the Upland-Low-Alkalinity rivers, might offer greater overall benefits for water-quality remediation at the national scale, relative to the magnitude of nutrient reductions required. This approach could help inform the prioritisation of nutrient remediation, as part of a directional approach to water quality management based on closing the gaps between current and target nutrient concentrations.
本研究通过联合分析全国乡村调查源头溪流和协调河流监测计划数据集，对英国源头溪流在更广泛的河流网络中的营养状况进行了首次全国范围内的评估。我们应用一种新的营养限制评估方法，通过对氮（N）、磷（P）和碳（C）消耗的三元评估，与 N:P 化学计量比和阈值 P 和 N 浓度相结合，来探索营养物质可能限制源头溪流和河流初级生产力的程度。河流中更常见磷限制，而源头溪流中更常见氮限制。在源头溪流中发现了高浓度的潜在 P 和 N 共限制，尤其是在高地-低碱性溪流中。这表明，为了最小化这些敏感的源头溪流环境退化的风险，可能需要管理 P 和 N 的输入。尽管局部的源头溪流营养物质损害可能会发生，但相对于下游河流，源头溪流的 P 和 N 损害率在全国范围内明显较低。与水文稀释相比，养分来源的贡献随着集水区规模的增加而增加，这与农业和城市土地利用的范围增加相对应。为了达到《水框架指令》的标准并达到限制浓度，实现合规所需的营养物质减少量在低地-高碱性河流和溪流中最大。初步评估表明，相对于所需的营养物质减少量，减少低地-高碱性源头溪流中的 P 浓度，以及高地-低碱性河流中的 N 浓度，可能会在全国范围内为水质修复带来更大的整体效益。这种方法可以帮助确定营养修复的优先级，作为基于当前和目标营养浓度差距的水质管理的定向方法的一部分。
