DOI: 10.5285/eeffacad-1f23-456a-aac0-1bda40958f75
title: Chemical and physical data of water and its evolution over incubation experiments for three headwater streams in the Conwy catchment, North Wales (2014)

description:  These data are chemical and physical data of stream water and their evolution over incubation experiments conducted on water samples taken from three headwater streams from the Conwy catchment in North Wales. Incubations involved different treatments, controlled light exposure, sterilization, and nutrient enrichment (nitrogen and phosphorus). The measured parameters are concentrations of organic carbon, total nitrogen, and major anions and cations and parameters such as pH, electrical conductivity, and absorbance. Samples were collected on two occasions for each stream between May 2014 and September 2014. Five litres of water sample were collected on the field and brought back to the laboratory for six-day incubations. Incubation started immediately after sampling. Incubation experiments were conducted in the Centre for Ecology & Hydrology laboratory, Bangor, United Kingdom. Incubations were carried out in a Bangor University laboratory using an experimental set-up built for allowing the control of light exposure. Analyses were performed in the Centre for Ecology & Hydrology (CEH) laboratory. The different treatments involved samples being kept in the dark or exposed to controlled light; additionally between 6 to 12 light-exposed samples were poisoned with Mercury(II) chloride (HgCl2) or enriched with nutrients (Nitrogen as nitrate, Phosphorus as phosphate or both).

The data were collected to understand the fate of dissolved organic carbon in headwater streams depending on its sources, nature and on the inorganic nutrients availability in the headwater streams. 

When there was a doubt on the values, the analysis was redone, all values in the database have been validated. 

The sampling, incubations and analyses where  performed by Ophelie Fovet, L'Institut National de la Recherche Agronomique (INRA) Rennes, L'Unité mixte de Recherche Sol Agro et hydrosystèmes Spatialisation (UMR SAS), France and co-ordinated by Chris Evans, CEH Bangor, Wales, UK.  
description: Water samples were collected with a 5 litre plastic bottle, extra 500 millilitre (ml) glass bottles were sampled for pH and alkalinity measurements. In the laboratory, 12 to 16 subsamples were taken to allow for 3 to 4 treatments replicated 4 to 3 times. For each subsample, 300 ml of water was taken and placed into amber bottles in the experimental set-up. The water was circulated between the amber bottle placed in a cooling bath and the vessels located in a Sun Test Box CPS+ with a peristaltic pump. From 12 to 16  vessels were covered over for the dark treatments. In each treatment, filtered subsamples were taken every day for analytical measurement For the poisoning treatments, 0.42 milligrammes per litre (mg/L) of a 10 grammes per litre (g/L) solution of Mercury (II) chloride (HgCl2) were added to the subsample. For the nutrient enrichment treatments, 1.5 mille grammes (mg) and 0.03 mg of Phosphorus were added to the amber bottle respectively from Sodium Nitrate (NaNO3) and Monosodium phosphate (NaH2PO) respectively. Major anion and cation concentrations in milligrammes per litre (mg/L) were determined by Ion Chromatography on a Dionex DX-120 instrument. pH (in pH unit) and Gran alkalinity in micro equivalents per litre (microeq/L) were measured by titration on a Metrohm 888 Titrando. Conductivity was measured using a Jenway 4320 conductivity meter. Major anion and cation concentrations and pH analyses were performed to demonstrate that the nutrient additions did not have an unexpected effect on the water quality. A comparison on the filtered and unfiltered water samples was also carried out.

Organic and Inorganic Carbon (OC and IC) concentration in millegrammes of Carbon per litre (mg of C/L) were measured on a Thermalox TC/TN Analyser. Total carbon (TC) was determined by thermal oxidation (680 Celsius degree) with detection of CO2 by an NDIR (Non Dispersive Infra-Red) sensor. Non Purgeable Organic Carbon (NPOC, in mg of C/L) was determined as for TC but with sample preparation involving spiking samples with 1M Hydrochloric Acid (HCl) and sparging for 60 seconds  with oxygen gas to remove inorganic carbon. Total Inorganic Carbon (TIC) in mg of C/L was determined as for TC, but with at a lower furnace operating temperature of 120 degrees Celsius and with phosphoric acid added to the reactor tube as a catalyst. For the Nant y Brwyn stream (peat, low concentration of IC) OC was measured as NPOC, while for the other streams (where IC was higher), OC was measured as the difference between TC and TIC, according to previous analyses which enabled us to identify the most suitable method considering differences between sample types. Total nitrogen (TN) in milligrammes of Nitrogen per litre (mg N/L) was determined using the Thermalox analyser by thermal oxidation (680 degrees Celsius) followed by ozonation of Nitrogen (N) to Nitrogen Oxides (NOx) and fluorescence detection. 

Sample pH (in pH unit) and Gran alkalinity in micro equivalents per litre (microeq/L) were measured by titration on a Metrohm 888 Titrando. Conductivity was measured using a Jenway 4320 conductivity meter.

Absorbance was measured at wavelengths from 200 to 700 nanometres (nm) using a Spectramax M2e plate reader. An ultrapure water (Milli-Q blank) reading was taken to subtract from each sample to have the 'true' absorbance value of the samples. Values at 254 nm were used to compute the Specific Absorbance to Ultra Violet, the E2/E3 ratio was computed as the ratio between values at 250 nm and 365 nm and the humification index as the ratio between values at 465 nm and 665 nm. Particulate organic carbon (POC) was measured by measuring Particulate Organic Matter (POM) and determining mass lost upon combustion of a sample at 550 degrees Celsius. Samples were filtered through Glass microfiber filter papers that had been purged of extraneous POC before filtration by combusting them at 550 degrees Celsius for 4 hours. After the filtration, filters were dried in an oven at 105 degrees Celsius for 3.5 hours, weighed, and then placed into a muffle furnace at 550 degrees Celsius C for 3 hours and weighed again. The difference between the two weights provided the POM concentration from which POC concentration is estimated assuming that Carbon represents 50 percent of this organic matter. If sample storage was necessary before the analysis, samples were kept in the dark and at less than 5 degrees Celsius.

For all analyses, instruments were calibrated in a range of values relevant for the nature of the water samples before each analyses run. Control standards and blank controls were systematically used at a relevant regular intervals. For analyses carried on TC/TN analyser, the coefficient of variations was controlled to be lower than a few percent. When there was a doubt on the values, the analysis was redone, all values in the database have been validated. Data were downloaded from the analytical machines and imported into an Excel spreadsheet to be analysed. The final data was exported as a comma separated value file for ingestion into the Environmental Information Data Centre.