The Role of Hydromorphology in the Partial Recovery of Chemistry in Acidified and Warmed Dutch Moorland Pools.

To monitor recovery from acidification, water chemistry was sampled in 11 Dutch moorland pools from 1978 to 2018. Changes were assessed by visual inspection of time series and tested non-parametrically. As a net result of all inputs and outputs, the median sulphate and ammonium concentrations in the surface water dropped by about 90%. This was accompanied by increases in pH, acid neutralizing capacity, and dissolved organic matter, and decreased metals, particularly toxic aluminium. Decreases of ammonium and sulphate in the surface water are considerably higher than in deposition, indicating the importance of losses to sediments and the atmosphere. The changes were greatest in pools with relatively flat banks exposed to the air in extremely dry summers. After the extremely dry summer of 1976, the changes were dramatic due to acidification by oxidation of the reduced sulphur and nitrogen compounds stored in the moorland pool bottom. In later dry years, the changes in the pools with flat banks were less extreme, as the sulphur stock in the sediment was depleted by winterly discharge to groundwater. In pools with steep banks, the sulphur compounds are retained in the sediment and may cause eutrophication by the displacement of phosphorus from iron compounds. [ABSTRACT FROM AUTHOR]