Consistency and uncertainty of UK measurements of mercury in precipitation.

A novel method to assess the uncertainty of measurement of mercury in precipitation for the UK's Heavy Metals Monitoring Network is presented. The method makes use of the fact that, because of the high risk of sample contamination, samples are taken in duplicate in order to ensure valid data is available for as many sampling periods as possible. Where both samples are valid a good opportunity is afforded to use the statistical differences in the rain volumes sampled and the mercury concentrations measured to assess the overall uncertainty of the measurement. This process has produced estimated uncertainties in good agreement with previous studies and well within the limits specified by European legislation. The work also highlighted an effective method to spot outliers in the paired samples at the data ratification stage.

High-frequency water quality time series in precipitation and streamflow: from fragmentary signals to scientific challenge.

Eighteen months of 7-hourly analyses of rainfall and stream water chemistry are presented, spanning a wide range of chemical determinands and building on over 20 years of weekly records for the moorland headwaters of the river Severn. The high-frequency time series data show that hydrochemical responses to major hydrological and biological drivers of short-term variability in rainfall and rivers are not captured by conventional low-frequency monitoring programmes. A wealth of flow related, flow independent, diurnal, seasonal and annual fluctuations indicate a cacophony of interactions within the catchment and stream. The complexity of the chemical dynamics is visually obvious, although there appears to be no clear way of translating this complexity into a simple algorithm. The work provides a proof of concept for the complex structure of catchment functioning revealed by extensive high-frequency measurements coupled with high analytical sensitivity and reproducibility. It provides new insights into hydrogeochemical functioning and a novel resource for catchment modelling.