Evaluation and optimisation of estuarine sampling uncertainty

Ricardo Bettencourt da Silva, CQE-FCUL - Universidade de Lisboa, 1749-016 Lisboa, Portugal (rjsilva@fc.ul.pt)
Carlos Borges, Instituto Hidrográfico, 1200-615 Lisboa, Portugal
Carla Palma, Instituto Hidrográfico, 1200-615 Lisboa, Portugal

The assessment of long-term pollution trends of the water of a river is affected by the seasonal variation of river conditions, the heterogeneity of pollutants distribution, the representativeness of the sampling and the uncertainty of samples analysis. This work presents a methodology to estimate the uncertainty of the characterisation of a river water area that was successfully applied to monitor nutrients in Tagus river estuary.

The heterogeneity of the system was described by a 3D surface with x and y variables for samples positions and z variable for the measured nutrient concentration. The randomisation of this surface for the uncertainty of the GPS coordinates and measured concentration, using Monte Carlo simulations, allowed estimating the uncertainty from single or composite sampling. The production of composite samples from three subsamples collected at 30 m distance allows a small sampling uncertainty. The relative expanded uncertainty of nutrients concentrations ranged between 5.7% and 10%.

Short Biography of Presenting Author

Prof. Ricardo J.N. Bettencourt da Silva after working in public and private laboratories as analyst and consultant for 15 years, started a research and teaching career at the Faculty of Sciences of the University of Lisbon. His research interests are Metrology and Examinology in chemistry, the sciences of measurements and qualitative analysis in chemistry, respectively. He collaborates in teaching at Master Courses of consortiums of various Universities. Since 2002, collaborates regularly with the Portuguese Accreditation Body, as technical assessor. Ricardo is currently Secretary of CITAC (www.citac.cc), member of the executive committee of Eurachem and chair of the Eurachem working group on Qualitative Analysis (www.eurachem.org). (website: http://webpages.fc.ul.pt/~rjsilva/

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