Nutrient concentration and stable isotope data from water samples across river-lake networks in the English Lake District and Norfolk Broads, 2017-2018

Water samples were collected from well-mixed areas of streams and rivers via bridges or from river banks. Samples of lake surface water (upper 30 cm of water column) were collected from pelagic zones via boats, or from the lake shore where logistical constraints prevented the use of boats. Water samples were analysed for field parameters (pH, EC, temperature) immediately, and then processed (filtration) in the field before storage on ice prior to return to the laboratory. Samples were stored in refrigerators or frozen (for isotope analysis) prior to analysis. A range of laboratory analyses were undertaken to determine the concentration of individual nutrient fractions and stable nitrate oxygen and nitrogen isotope composition.

Field blanks, using >18.2 M Ω milliQ-grade laboratory water, were included in each sampling visit and confirmed no contamination occurred during sample collection or processing. Calibrations for nutrient concentration analyses were confirmed using externally-certified reference standards. Repeated analysis of 10% of samples, selected at random, was used to evaluate precision of the analytical approaches for nutrient concentration analyses. Raw stable isotope values were calibrated using international standards. All international standards were run in triplicate, as well as an internal nitrate standard for quality control measures. At least one environmental sample in each run was also analysed in triplicate.

Data were entered into a spreadsheet and manually checked for transcription errors.

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