The Alberta Research Council (ARC), AMEC Earth & Environmental Limited (AGRA) and the University of Alberta were requested by the NOx-SO2 Management Working Group to provide soils and peatlands data for development of acidification critical loads maps. The specific objectives of the soils component of the receptor sensitivity mapping project were to determine critical loads of acid deposition on soils, and to provide the critical loads data in a format suitable for incorporation in a geographic information system database of receptors. The scope in terms of soil types and ecosystems comprised all upland (mineral) soils and all Organic (or peat) soils. The approach with respect to mineral soils entailed simulation of soil acidification by application of a dynamic soil acidification model to mineral soils. The model includes a module for organic material (LFH) acidification based on its buffer capacity. In the case of Organic soils, the modelling of acidification over time was based on the acid buffer capacity of peat and of peat water.
Major project components included compilation of model input data from existing sources, application of the ARC soil acidification model, sampling of soils (surface organic layers and peats), buffer capacity determination and modelling of organic soil materials, derivation of critical loads from the model results, and development of a database of soil types and their critical loads.
Soil and peatland data sources were reviewed in order to obtain data for inputs into the soil simulation model. These included the AOSERP soil survey, soil surveys of earlier oil sands projects (Syncrude, OSLO, Alsands), and more recent soil survey components of EIAs (Suncor, Syncrude/Aurora, Shell, etc.). Most of the soils data was obtained from the AOSERP soil survey as only some of the data from the earlier surveys were suitable as input data for modelling. The more recent surveys had very little data, especially with respect to cation exchange capacity and exchangeable cations that could be applied in modelling.
The soil acidification simulation model applied for deriving critical loads had been developed through various soil acidification projects at the Alberta Research Council (ARC). However, it required modification particularly in terms of adding an organic soil module to simulate buffering in the litter (LFH) layers of mineral soils. The inclusion of appropriate chemical process terms in the model was also required as it had not previously been applied to peat (organic) soils.
Application of the ARC model as a two-layer model involved sequential simulation of chemical changes first on the litter layer, and then on the 0-25 cm mineral layer. All incoming acidity (wet and dry deposition, or potential acid input) was assumed to react first with the LFH layer. The water flowing through after reacting with the LFH layer was assumed to react in the 0-25 cm layer of the mineral soil. The proportion of water passing through the 25 cm layer was assumed to carry with it an equal proportion of the reaction products from that layer. Thus, although the majority of acidification impact occurs in the upper 25 cm of mineral soil and in the litter layer, a portion of the acidification impact occurs below the 25 cm layer.The Alberta Research Council (ARC), AMEC Earth & Environmental Limited (AGRA) and the University of Alberta were requested by the NOx-SO2 Management Working Group to provide soils and peatlands data for development of acidification critical loads maps. The specific objectives of the soils component of the receptor sensitivity mapping project were to determine critical loads of acid deposition on soils, and to provide the critical loads data in a format suitable for incorporation in a geographic information system database of receptors. The scope in terms of soil types and ecosystems comprised all upland (mineral) soils and all Organic (or peat) soils. The approach with respect to mineral soils entailed simulation of soil acidification by application of a dynamic soil acidification model to mineral soils. The model includes a module for organic material (LFH) acidification based on its buffer capacity. In the case of Organic soils, the modelling of acidification over time was based on the acid buffer capacity of peat and of peat water.
Major project components included compilation of model input data from existing sources, application of the ARC soil acidification model, sampling of soils (surface organic layers and peats), buffer capacity determination and modelling of organic soil materials, derivation of critical loads from the model results, and development of a database of soil types and their critical loads.
Soil and peatland data sources were reviewed in order to obtain data for inputs into the soil simulation model. These included the AOSERP soil survey, soil surveys of earlier oil sands projects (Syncrude, OSLO, Alsands), and more recent soil survey components of EIAs (Suncor, Syncrude/Aurora, Shell, etc.). Most of the soils data was obtained from the AOSERP soil survey as only some of the data from the earlier surveys were suitable as input data for modelling. The more recent surveys had very little data, especially with respect to cation exchange capacity and exchangeable cations that could be applied in modelling.
The soil acidification simulation model applied for deriving critical loads had been developed through various soil acidification projects at the Alberta Research Council (ARC). However, it required modification particularly in terms of adding an organic soil module to simulate buffering in the litter (LFH) layers of mineral soils. The inclusion of appropriate chemical process terms in the model was also required as it had not previously been applied to peat (organic) soils.
Application of the ARC model as a two-layer model involved sequential simulation of chemical changes first on the litter layer, and then on the 0-25 cm mineral layer. All incoming acidity (wet and dry deposition, or potential acid input) was assumed to react first with the LFH layer. The water flowing through after reacting with the LFH layer was assumed to react in the 0-25 cm layer of the mineral soil. The proportion of water passing through the 25 cm layer was assumed to carry with it an equal proportion of the reaction products from that layer. Thus, although the majority of acidification impact occurs in the upper 25 cm of mineral soil and in the litter layer, a portion of the acidification impact occurs below the 25 cm layer.