Uncertainties in annual riverine phosphorus load estimation: Impact of load estimation methodology, sampling frequency, baseflow index and catchment population density
Uncertainties in annual riverine phosphorus load estimation: Impact of load estimation methodology, sampling frequency, baseflow index and catchment population density
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DOI：
10.1016/j.jhydrol.2006.07.006
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发表时间：
2007-01-01
影响因子：
6.4
通讯作者：
Johnes, P. J.
中科院分区：
文献类型：
--
作者：
Johnes, P. J.
为确定从陆地向河流输出养分的速率和来源而开发的模型需要对水体中存在的养分负荷进行准确评估，以便校准模型参数和结构。这些数据很少以具有代表性的规模和适当的化学形式提供，除非在研究集水区。与基于这些数据的营养负荷估计相关的观测误差导致建模和营养预算研究中的高度不确定性。在这里，17个英国研究集水区的每日配对瞬时磷和流量数据覆盖了总共39个水年（WY），用于探索与基于部分分式和不频繁采样的养分通量估计相关的观测误差的性质和程度。每天的记录被人为删除，从每个WY和流域产生7个分层采样记录、7个周记录和30个月记录。这些被用来评估采样频率对负荷估计不确定度的影响。分析强调了基于月度数据和单个P分数而不是总P的负荷估计的高度不确定性。当采样频率较低时，发现具有高基流指数和/或低人口密度的集水区在负荷估计上的RMSE低于具有低基流指数和高人口密度的集水区。集水区大小并没有被证明是重要的，尽管本研究的一个局限性是，每日记录可能无法捕捉到较小的集水区中P输出行为的全部范围，并使用华丽的水文图，导致低估了这些集水区负荷估计的不确定性。为了充分调查这一点，需要进一步分析亚日记录。本文就以不同频率采样的不同流域类型的负荷估算方法提出了建议，并介绍了这种分析可用于识别模型校准和营养预算研究的观测误差和不确定性的方法。(c) 2006 Elsevier B.V.版权所有
Models developed to identify the rates and origins of nutrient export from land to stream require an accurate assessment of the nutrient load present in the water body in order to calibrate model parameters and structure. These data are rarely available at a representative scale and in an appropriate chemical form except in research catchments. Observational errors associated with nutrient load estimates based on these data lead to a high degree of uncertainty in modelling and nutrient budgeting studies. Here, daily paired instantaneous P and flow data for 17 UK research catchments covering a total of 39 water years (WY) have been used to explore the nature and extent of the observational error associated with nutrient flux estimates based on partial fractions and infrequent sampling. The daily records were artificially decimated to create 7 stratified sampling records, 7 weekly records, and 30 monthly records from each WY and catchment. These were used to evaluate the impact of sampling frequency on load estimate uncertainty. The analysis underlines the high uncertainty of load estimates based on monthly data and individual P fractions rather than total P. Catchments with a high baseflow index and/or low population density were found to return a lower RMSE on load estimates when sampled infrequently than those with a tow baseflow index and high population density. Catchment size was not shown to be important, though a limitation of this study is that daily records may fail to capture the full range of P export behaviour in smaller catchments with flashy hydrographs, leading to an underestimate of uncertainty in Load estimates for such catchments. Further analysis of sub-daily records is needed to investigate this fully. Here, recommendations are given on load estimation methodologies for different catchment types sampled at different frequencies, and the ways in which this analysis can be used to identify observational error and uncertainty for model calibration and nutrient budgeting studies. (c) 2006 Elsevier B.V. All rights reserved.