Data quality in laboratories: methods and results for soil, foliar and water chemical analyses

Chemical analyses are an essential part of forest ecosystem monitoring activities that entail the determination of nutrient and pollutant fluxes in forest ecosystems. The value of chemical data depends to a great extent on the quality of the analytical work provided by the laboratories involved in the monitoring. To maximize the spatial and temporal comparability of monitoring data over time, every effort must be taken to ensure accuracy of the analytical measurements. This has been done in forest monitoring in Europe within the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). In this context, different expert panels and groups have developed a comprehensive Quality Assurance (QA) and Quality Control (QC) program for the participating laboratories over the past two decades. As part of this drive to improve the inter- and intracomparability of analytical data, the laboratories have participated in a number of interlaboratory calibration exercises (otherwise known as ring tests) and held extensive discussions on harmonizing and improving the use of analytical methodology and QA/QC procedures. This chapter presents an overview of the QA/QC criteria that have been devised for the relevant fields of analytical chemistry in international forest monitoring in Europe, including the analysis of atmospheric deposition, soil solution, soil, foliage, and litterfall samples. Additional information on the quality checks and reference standards used, ring tests, and QC results is also provided.