Earth Sciences Report 1987-01

Soil sensitivity to acid deposition and the potential of soils and geology in Alberta to reduce the acidity of acidic inputs

Authors: Holowaychuk, N.; Fessenden, R.J.

Executive Summary

The objective of this project was to prepare maps of the province of Alberta, suitable for presentation at a scale of 1:2 000 000, showing the distribution of soils relative to their sensitivity to acid deposition and the distribution of soils and geology relative to their potential to reduce the acidity of atmospheric deposition. This project was Alberta's contribution to a Western Canada Long Range Transport of Air Pollution (LRTAP) Committee effort to prepare such maps for the four western provinces, the Yukon, and the Northwest Territories in a coordinated and collaborative fashion.

When this project was initiated, no soils base map W8S available for the province of Alberta that was suitable for interpreting Fe sensitivity of soils to acid deposition or their potential to reduce the acidity of atmospheric deposition. Descriptive information was assembled and synthesized for mineral soils and peatland systems throughout the province. Approximately 350 discrete map units were delineated; these were consolidated into 215 distinct map unit types. The quality and detail of the soils information that was available for the southern half of the province and the Peace River area, and the National Parks in the Rocky Mountains, was quite good. However, the information that was available for the far north and the northeastern areas of the province, and the eastern slopes, was more general In particular, there was a paucity of information for Organic and Organic Cryosol soils, except in a few localized areas.

The sensitivity of mineral soils to acid deposition was Interpreted according to criteria that were developed cooperatively by the western Canada participants. The sensitivity of three soil processes-sensitivity to base loss, sensitivity to acidification, and sensitivity to the solubilization of aluminum - were rated separately for each map unit. These were then combined into an overall sensitivity rating. Soils mat were considered to have low base reserves, as evidenced by low cation exchange capacity and low pH, were rated as highly sensitive to acid deposition. Those soils that were considered to have high base reserves, as evidenced by a high cation exchange capacity and high pH, were rated as being of low sensitivity to acid deposition.

A provisional set of criteria was developed for Organic and Organic Cryosol soils. Three peatland system categories were recognized: eutrophic, mesotrophic, and oligotrophic. They were defined on the basis of pH and base cation content of the organic matrix-ambient water systems. Eutrophic peatland systems, such as those with slightly acid to mildly alkaline reaction and relatively high base cation content, are considered to be of low sensitivity. Mesotrophic peatland systems, considered to be the predominant kind in Alberta, have low to intermediate pH and base cation content and are rated as being of high sensitivity. Oligotrophic peatland systems, those with the lowest pH and base cation content, are considered to be of low sensitivity because they are well buffered in the extremely to very strongly acid range by aluminum and humic acid buffering systems.

Expressed as a percentage of the total area of the province, soils of high sensitivity occupy 22.7 percent, soils of medium sensitivity occupy 30.6 percent, and soils of low sensitivity occupy 44.4 percent. The major groups of soils in the high sensitivity category are the mesotrophic peatlands and Dystric Brunisols, both of which are primarily boated in the northeastern region of the province. The major groups of soil placed in the medium sensitivity category are the various subgroups of me Gray Luvisolic great group. These soils have very extensive distribution in the central and eastern slopes regions of the province. The largest group of soils in the low sensitivity category comprises the Chernozems, located in the southern and central regions of the province.

All map units were a/so rated for their potential to reduce the acidity of atmospheric deposition. The criteria that were used for mineral soils were developed jointly by the western Canada participants and were based on criteria developed in eastern Canada. They are based on combinations of soil depth, exchangeable base content , bedrock type, parent material type, and soil drainage class. Criteria for Organic soils were not developed by the LRTAP committee. Provisional criteria were developed for Alberta and used in this project.

Expressed as a percentage of the total area of the province, soils (and associated geology) with high potential to reduce acidity occupy 64.4 percent, soils with medium potential, 21.8 percent, and soils with low potential, 11.3 percent. Most of the southern half of the province and the Peace River region are occupied by soils with a high potential to reduce acidity. Soils with medium potential are located predominantly in the north central, northeastern and eastern slopes regions, and to some extent in the Rocky Mountains. Soils with low potential are located in the far north, the northeastern regions of the province, and the northern Rocky Mountains, and are associated with oligotrophic peatland systems and coarse-textured, acid, Dystric Brunisol soils. Eutrophic peatland systems are considered to have a high potential to reduce acidity, mesotrophic peatland systems have a medium potential, and oligotrophic systems, a low potential.

Place Keywords: 72e; 72l; 72m; 73d; 73e; 73l; 73m; 74d; 74e; 74l; 74m; 82g; 82h; 82i; 82j; 82n; 82o; 82p; 83a; 83b; 83c; 83d; 83e; 83f; 83g; 83h; 83i; 83j; 83k; 83l; 83m; 83n; 83o; 83p; 84a; 84b; 84c; 84d; 84e; 84f; 84g; 84h; 84i; 84j; 84k; 84l; 84m; 84n; 84o; 84p; alberta; canada

Theme Keywords: acid input; geology; soil acidity; soil sensitivity