Recovery data for surface water, groundwater and lab reagent samples analyzed by the USGS National Water Quality Laboratory schedule 2437, water years 2013-15.

Analytical recovery is the concentration of an analyte measured in a water-quality sample expressed as a percentage of the known concentration added to the sample (Mueller and others, 2015). Analytical recovery (hereafter referred to as “recovery”) can be used to understand method bias and variability and to assess the temporal changes in a method over time (Martin and others, 2009). This data set includes two tables: one table of field spike recovery data and one table of lab reagent spike recovery data. The table of field spike recovery data includes results from paired environmental and spike samples collected by the National Water Quality Program, National Water-Quality Assessment (NAWQA) Project in surface water and groundwater. These samples were collected as part of the NAWQA Project’s National Water Quality Network: Rivers and Streams assessment, Regional Stream Quality Assessment studies and in multiple groundwater networks following standard practices (Mueller and others, 1997). This table includes environmental and spike water-quality sample data stored in the USGS National Water Information System (NWIS) database (https://dx.doi.org/10.5066/F7P55KJN). Concentrations of pesticides in spike samples, while stored in the NWIS database, are not publically available. The calculation of recovery based on these field sample data is outlined in Mueller and others (2015). Lab reagent spikes are pesticide-free reagent water spiked with a known concentration of pesticide. Lab reagent spikes are prepared in the lab and their recovery can be directly measured. The table of lab reagent spike data contains quality control sample information stored in the USGS National Water Quality Laboratory (NWQL) database. Both tables include fields for data-quality indicators that are described in the data processing steps of this metadata file. These tables were developed in order to support a USGS Scientific Investigations Report with the working title “Considerations for the Preparation of Pesticide Data Analyzed with National Water Quality Laboratory Schedule 2437”. Martin, J.D., Stone, W.W, Wydoski, D.S., and Sandstrom, M.W., 2009, Adjustment of pesticide concentrations for temporal changes in analytical recovery, 1992–2006: U.S. Geological Survey Scientific Investigations Report 2009–5189, 23 p. plus appendixes. Mueller, D.K., Schertz, T.L., Martin, J.D., and Sandstrom, M.W., 2015, Design, analysis, and interpretation of field quality-control data for water-sampling projects: U.S. Geological Survey Techniques and Methods, book 4, chap. C4, 54 p., https://dx.doi.org/10.3133/tm4C4. Mueller, D.K., Martin, J.D. and Lopes, T.J., 1997, Quality-Control Design for Surface-Water Sampling in the National Water-Quality Assessment Program: U.S. Geological Survey Open-File Report 97-223, 8 p. plus appendixes.

分析回收率（Analytical recovery）是指水质样品中测得的分析物浓度，与向样品中添加的已知浓度的百分比值（Mueller等，2015）。
分析回收率（以下简称“回收率”）可用于研判分析方法的偏倚与变异性，并评估方法的时间动态变化（Martin等，2009）。
本数据集包含两张数据表：一张为野外加标回收率数据表，另一张为实验室试剂加标回收率数据表。
野外加标回收率数据表包含由美国国家水质计划、国家水质评估（NAWQA）项目在地表水与地下水中采集的配对环境样品与加标样品的检测结果。
这些样品作为NAWQA项目国家水质网络的一部分采集，涵盖河流与溪流评估、区域溪流质量评估研究，以及遵循标准规范的多个地下水网络采集的样品（Mueller等，1997）。
该数据表包含存储于美国地质调查局（USGS）国家水信息系统（NWIS）数据库中的环境与加标水质样品数据（https://dx.doi.org/10.5066/F7P55KJN）。
尽管加标样品中的农药浓度存储于NWIS数据库中，但并未对外公开。
基于这些野外样品数据的回收率计算方法详见Mueller等（2015）的研究。
实验室试剂加标样是指向不含农药的试剂水中加入已知浓度的农药制备而成的样品。
实验室试剂加标样在实验室中制备，其回收率可直接测定。
实验室试剂加标回收率数据表包含存储于美国地质调查局（USGS）国家水质实验室（NWQL）数据库中的质控样品信息。
两张数据表均包含数据质量指标字段，相关说明详见本元数据文件的数据处理步骤。
本数据集的两张数据表旨在支撑美国地质调查局（USGS）一份暂定标题为《针对采用国家水质实验室2437号计划表（National Water Quality Laboratory Schedule 2437）分析的农药数据制备的考量》的科学调查报告。

Martin, J.D.、Stone, W.W.、Wydoski, D.S. 及 Sandstrom, M.W.，2009年，《1992–2006年针对分析回收率时间变化的农药浓度调整》：美国地质调查局科学调查报告2009–5189，共23页及附录。
Mueller, D.K.、Schertz, T.L.、Martin, J.D. 及 Sandstrom, M.W.，2015年，《水质采样项目野外质控数据的设计、分析与解读》：美国地质调查局技术与方法丛书第4册，第C4章，共54页，https://dx.doi.org/10.3133/tm4C4。
Mueller, D.K.、Martin, J.D. 及 Lopes, T.J.，1997年，《国家水质评估计划中地表水采样的质控设计》：美国地质调查局公开文件报告97-223，共8页及附录。