When accrediting an environmental monitoring programme, including sampling, storage and analyses of seawater, it is desirable to provide an estimate of the uncertainty of individual components that affect the results, The aim of this study was to clarify the significance between different contributors to the total uncertainty. The Mann-Whitney statistical test showed that the uncertainty associated with sampling conditions was significant when analysing ammonia, nitrite and phosphate, Analyses of ammonia, also showed that the fine structure 'patchiness' of the seawater, reinforced the outdoor contribution of uncertainty.