Algal primary production of Welsh upland rivers in response to organic matter addition (2013)

Dr Isabelle Durance was responsible for organising the surveys, Dr Hugh Feeley, Dr Anne-Laure Sauvadet and Marian Pye were in charge of collecting, processing and sorting the samples. The work was carried out under Diversity in Upland Rivers for Ecosystem Service Sustainability (DURESS) project (Grant reference NERC NE/J014818/1). DURESS was a project funded by the Natural Environment Research Council (NERC) Biodiversity and Ecosystem Service Sustainability (BESS) programme. | Each stream was divided into an upstream control zone and a downstream experimental zone.

Samples of algal biofilm were collected from tiles previously placed on each sampling site. Deciduous leaves were added directly to the stream and by fixing Onion bags of leaves the stream bed and bank. Algal samples were collected two occasions, January (3-16/01/2013), and March (11-14/03/2013) in all the streams in both the upstream reference zones and downstream experimental zones.

Six experimental units (algal tiles) were placed randomly in each reach of the experimental sites before and after the manipulation. Chlorophyll a accrual on tiles was used as a proxy measure of algal production and herbivory rates measured over the sampling periods (after Hladyz et al. 2011). Unglazed ceramic tiles (100 millimetres x 100 millimetres) were glued in pairs to house bricks, which were fixed to the benthos with a rebar stake placed through a hole in the brick centre.

The vertical edges of one tile on each brick were coated with a layer of petroleum jelly to deter crawling gazers, and the other tile was left as a control, to assess the strength of grazing pressure. Chlorophyll was extracted using acetone, and the concentration subsequently measured spectrophotometrically (after Layer et al. 2010). Data was entered into an Excel spreadsheet and then exported as a comma separated value file for ingestion into the Environmental Information Data Centre.