The present is the key to the past, but what does the future hold for the recovery of surface waters from acidification?

Analogue matching was used to identify close modern water quality analogues for a set of 59 acid-sensitive lakes in the Galloway region of south-west Scotland. Modern analogues were identified that closely matched the pre-disturbance conditions of these lakes using simulated water quality parameters from the MAGIC (Model of Acidification of Groundwater in Catchments) model for key years from 1860 to 2100. The lakes were matched with hydrochemical samples from a large spatial data set in the UK. For the majority of the 59 lakes, several close modern analogues were identified from the training set for specified years. The close modern analogues for the reference year (1860) were predominantly located in north-west Scotland, an area of low acid deposition and high-status water quality. A clear recovery in the regional surface water acid neutralising capacity (ANC) was simulated by MAGIC in 2015 compared to the situation in 1970 at the height of acid emissions. Predicted trends in surface water chemistry from present day to 2015 indicate some improvement in water quality with c. 23 +/- 0.97% recovery towards pre-acidification (1860) ANC for the region. Output from the MAGIC model was used with the analogue technique to investigate the combined influence of future changes in deposition and climate on biogeochemical processes and water quality at the Round Loch of Glenhead (RLGH). Our results demonstrate that pre-acidification restoration targets will not be achieved by simply reducing acid deposition, and climate change will further confound the beneficial effects of deposition reductions. Results for 2015 and beyond show that modern analogues for these periods were predominantly concentrated in North Wales, with some in north-west Scotland, Galloway and the Lake District. Evidence from model simulations and modern analogues indicate that more stringent measures to further reduce acid deposition and combat climate change in the future are necessary if the majority of lakes in the Galloway region are to be restored to their pre-acidification target chemistry. The identified analogues for selected periods may be used to study wider ecological conditions to better define reference conditions and future recovery trajectories. That modern analogues were identified for the simulated chemistry in 2100 at RLGH suggests that unprecedented chemical conditions are unlikely to be observed as a result of future climate change.