Water quality survey of streams across Wales: runoff from forested and felled catchments draining a range of soil types

Sampling sites were chosen across Wales on the basis of: 1) Each catchment had to represent single soil and tree type as well as management scheme; 2) Each catchment had a definable boundary and it contained a first order stream draining it; 3) Catchment areas had to be small (2 to 5 ha); 4) The sites had to be completely forested or completely harvested; 5) Site details had to be available including information on soil and tree types, times of tree planting and harvesting (plus tree replanting in a limited number of cases); 6) The availability of Forest Enterprise staff to collect samples. Each sampling team were provided with an appropriate variety of cleaned plastic and glass bottles to collect samples that could be processed for major, minor and trace elements etc. The sampling was triggered by an alert from CEH staff of appropriate weather conditions. These alerts were for extended dry periods, to assess baseflow chemistry, and regional storm conditions in order to sample stormflow. The samples were taken to the local Forest Enterprise office soon after collection. They were then dispatched (mainly on the day of sample collection), to the (then) CEH site at Staylittle, mid-Wales, for processing. The next working day at CEH Staylittle, pH and Gran titration assays were made. The remaining samples were filtered (0.45µM) and the filtrates were stored in the appropriate bottles for shipment to CEH Wallingford for further chemical analysis. In the case of metal analysis, the samples were acidified prior to analysis in order to eliminate storage artefacts. For pH measurements, the samples were stored filled in glass bottles with immediate analysis on opening to avoid carbon dioxide degassing that would lead to a rise in pH. At the Forest Enterprise and CEH offices the samples were stored in the dark at 4°C in order to eliminate other storage artefacts. The data presented is 'raw' and has not been edited to include less than values etc. Contained within the metadata is a file that gives all the analytical methods used, including information on detection levels etc. This allows the user to adjust the data to standard protocols for presenting an edited dataset. In addition, metadata files are provided to describe site locations (grid references) and associated information (soil types, tree species and felling dates etc.) as well as field sampling and other protocols prior to chemical analysis.