Following the success of liming in and upstream of Llyn Brianne Reservoir, Environment Agency Wales (EAW) trialled an alternative liming method, using granular limestone sand, in the Tywi and Teifi catchments between 2004 and 2007. The trials were funded through the Fishing Wales Project (European Regional Development Fund) and they demonstrated that this method could effectively reduce the impact of acid episodes during high flows. Carmarthenshire Rivers Trust (more recently West Wales Rivers Trust) then received European Fisheries Funding and Welsh Government match funding to use the limestone sand method in the Afon Doethie.

The Afon Doethie is a tributary of the Afon Tywi downstream of Llyn Brianne Reservoir. Salmon and sea trout are unable to migrate upstream of the the reservoir, so the Doethie and its main tributary, the Afon Pysgotwr, are important for fish spawning and juvenile development. These spawning and nursery grounds were, however, identified as being adversely affected by acidification towards the end of the twentieth century (Scarr et al, 2001).

Limestone sand was applied at 9 sites in the Doethie catchment by Carmarthenshire Rivers Trust from 2010, following the method of Menendez (2000). Initially, 68 tonnes of relatively coarse-grained (1-5mm) limestone sand were applied during high flow events each year, divided into 34 tonnes in both spring and autumn. The annual dose rate was doubled in 2013 and a combination of 60% fine grained (1-3mm) and 40% coarser grained (1-5mm) sand was used in an attempt to improve the efficacy of the liming (Harper, 2015). Natural Resources Wales continued the former role of EAW in supporting these limestone sand projects and carrying out surveys to assess the ecological benefits.

References

Harper, AR (2015) A long-term assessment of the impacts of liming on macro-invertebrates in the Doethie sub-catchment of the Afon Tywi, Central Wales. MSc dissertation, Swansea University

Menendez R, Clayton JL & Zurbuch PE (2000) Sand-Sized Limestone Treatment of Streams Impacted by Acid Mine Drainage. Water, Air, & Soil Pollution 124, 411-428 (2000)

Scarr, A, Edwards P & Bishop M (2001) Acid waters remediation and long-term monitoring in Wales. Environment Agency Wales R&D Technical Report P2-246