Determination of river water composition trends with uncertainty: Seasonal variation of nutrients concentration in Tagus river estuary in the dry 2017 year

• Published in: Marine pollution bulletin Vol. 158; p. 111371
• Main Authors: Borges, Carlos, Bettencourt da Silva, Ricardo J.N., Palma, Carla
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2020; Elsevier BV
• Subjects: Algae; Composition; Composition trends; Confidence intervals; Dissolved nutrients; Dissolved oxygen; Estuaries; Estuarine dynamics; Freshwater; Heterogeneity; Inland water environment; Measurement uncertainty; Mineral nutrients; Monte Carlo simulation; Nitrogen compounds; Nitrogen dioxide; Nutrient concentrations; Nutrients; Oxides; River water; Rivers; Sampling; Seasonal variability; Seasonal variation; Seasonal variations; Silica; Silicon dioxide; Statistical methods; Tagus river; Trends; Uncertainty; Uncertainty analysis; Seasonal variability; Composition trends; Dissolved nutrients; Tagus river; Measurement uncertainty
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2020.111371

The assessment of long-term trends in river water composition is hampered by river composition heterogeneity, and sampling and sample analysis uncertainty. This work describes a novel methodology for the reliable detection of small river composition trends by taking all relevant uncertainty components into account. The methodology was applied to study the variation of nutrients concentration of Tagus river estuary in the extremely dry 2017 year. Mean nutrient concentrations were determined with an uncertainty that combines sampling and sample analysis uncertainty by the Monte Carlo Method. The nutrient concentration variation observed in two occasions is meaningful if the difference of mean concentrations is metrologically different from zero for a 95% confidence level. The observed meaningful NO2 increase, and SiO2 and NOx variations is justified by dissolved oxygen reduction, decreased freshwater input and algal productivity variations. The developed tool can be applied to the assessment of other composition trends in rivers. [Display omitted] •Methodology for distinguishing small composition trends of a large river area•Concentration variations determined with sampling and sample analysis uncertainty•Variation of nutrients concentrations in Tagus river estuary in the very dry 2017•NO2, SiO2 and NOx variations justified by physicochemical and biological processes