IntroductionOver the last 20-40 years major progress has been made in characterizing the hydrochemical functioning of catchments based on extensive, high-quality monitoring programmes. These data are vital for addressing issues, such as long-term responses of streams to external pressures, to assess the environmental impact. This is critical, for example, in relation to the issue of acidic deposition ( 3818 INVITED COMMENTARYRaw data and data edited to remove likely errors are provided on the CEH Information Gateway, and it is for the user to make informed judgements concerning analysis and interpretation. For the future, a universal standard will need to be developed and applied in the context of changing methodologies, which determine detection limits and sensitivity. However, informed judgement can only come with the provision of raw data as it is impossible to go back to the original values once the data have been censored and subsequently stored. This article not only flags the database but also includes references to published work and comments on new findings. While we recognize the importance of making data as freely available as possible, this is performed in relation to the institutional copyright for the data and recognition of previously published work. These are critical performance indicators that give value and endorsement to ensure the long-term continuation of major environmental monitoring programmes. We point out the logistical challenge of bringing the information together. This is important to recognize the amount of time that may be needed. We urge ongoing and future research to put data management systems in place that are robust, requiring minimum retrospective modification to cope with the potential loss of background knowledge that may occur when staff leave or research priorities change.

This scientific briefing announces the availability of a new multi-element high-frequency water quality data set that is openly accessible to the research community. The data set comprises up to two years of seven-hourly water quality data for two streams and one rainfall site in the Upper Severn catchment at Plynlimon in mid-Wales. The measurements cover 50 analytes ranging from H + to U and spanning six orders of magnitude in concentration, including major, minor, and trace elements as well as nutrients, and they complement decades of weekly measurements of the same analytes at the Upper Severn. Together they provide a unique data set for studying both long-term trends and short-term dynamics. Archives and metadata for both the seven-hourly and weekly measurements accompany this scientific briefing as supplementary online information. The data show complex behaviour over a wide range of timescales, challenging our understanding of catchment processes and informing future modelling efforts.

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