Aluminium speciation in soils and surface waters under impact of acid rain
Chapter 1: The emissions, transformation and deposition of Acid Rain are outlined in this chapter as well as the interaction of acid precipitation with vegetation and the mechanisms of soil acidification. The possible pathways for the release of aluminium in soils are discussed as well as an introduction to aqueous aluminium chemistry and aluminium speciation techniques. Chapter 2: The sites descriptions of the Loch Ard, Allt a Mharcaidh and Hoylandet catchments are presented. The methods of sample collection by field instrumentation and aluminium determination in water samples are also described. Details of soil extraction techniques applied to all the horizons of the soils in the catchments are given. The concentration of available solid phase aluminium in the soils is presented. Chapter 3: The Loch Ard catchment was used for the study of aluminium speciation in soils and surface waters of acidified catchments. Two soil types under different vegetations were examined and an aluminium budget study of input, vegetation, soil and stream waters was presented. Chapter 4: Aluminium speciation in three soil types in the Allt a Mharcaidh catchment was studied. An absolute budget of Al release was not presented but variations in Al species in waters from soil and streams over the sampling period were presented. Chapter 5: Episodic events at both Hoylandet (Norway) and Loch Ard (Scotland) were studied. The event in Norway was due to spring snowmelt while the event at Loch Ard was rainstorm event. The chemical response to large fluctuations in percolating waters through soils resulting in increased stream flow as monitored over short time periods, particularly in relation to changes in aluminium species. Chpater 6: A laboratory controlled leaching experiment on an alpine podzol and peaty podzol soil from the Allt a Mharcaidh catchment was undertaken using both mineral (sulphuric) and organic (citric) acids. The purpose of the experiment was to determine the potential release of aluminium from soil horizons acidified by different acidic inputs. It also investigated the possible soil mechanisms resulting in the release of aluminium, particularly sulphate saturation and cation exchange reactions. Chapter 7: The response of stream sediment to release aluminium into waters subjected to increased acidification was studied in both laboratory and catchment-based experiments. The results indicated the valuable source of aluminium in stream beds which must be considered in determining a proper aluminium budget for a catchment study. Chapter 8: A preliminary study of the organic complexation of aluminium with naturally occurring organic acids and three different fulvic acids is presented. The study outlines the difficulty in predicting complexation particularly for fulvic acids where major molecular structural differences account for the degree of complexation. Chapter 9: Summary and conclusions.