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Title: Hydrological pathways, aluminium mobilisation and streamwater acidity in an afforested catchment in upland Wales
Author: Soulsby, C.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1991
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This thesis considers the problem of stream acidification in afforested catchments at Llyn Brianne, upland Wales. The main focus for study is the way in which hydrological pathways and soil chemical processes influence the acidity and aluminium levels in streamwaters. Within a 253ha experimental catchment, two small sub-catchments and study plots were instrumented to monitor the movement of water from the atmosphere, through the forest canopy and underlying soils, into streams. Water was sampled at various stages of its hydrological pathway to characterize its chemical composition. The study centred on the movement of water and solutes through Sitka spruce forest systems on two different soil types which cover large areas of upland Wales: cambic stagnohumic gleys and ironpan stagnopodzols. Precipitation at the study sites was acidified and enriched in mobile anions by enhanced atmospheric deposition on the forest canopy. The subsequent increased concentration and flux of anions in the two acid study soils was found to mobilize aluminium by cation exchange processes and leach aluminium and hydrogen ions from the soil zone. Buffering reactions in the soil parent materials were found to neutralize some acidity in the deeper groundwater zone. Hydrological pathways through the two soils controlled the transfer of acidity and aluminium to surface waters. At baseflows, streamwater draining from the gley soils was derived from the groundwater zone; this was well-buffered with a low aluminium content. During storm events, runoff was generated by saturated throughflow in the near-surface soil horizons; this was acidic with high aluminium concentrations. Water draining from the podzols was derived from the deeper soil horizons and shallow slope drifts. This also provided a source of acid, aluminium-rich runoff during storm periods. The implications of these results to the understanding and management of stream acidification in afforested catchments are evaluated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available