A previous Research Memo No. 8 discussed the distribution of humus fractions, whereas this Research Memo will discuss optical properties of humic acid (HA) fractions. Solutions of HA are more or less brown colored; a measure of their coloration is called optical density (OD), which is determined on a spectrophotometer. The values obtained are further converted to two expressions: E400 (index of color intensity of HA solution) and E4/6 (extinction ratio). The aims of this study were to assess the extent to which forest ecosystems could be recognized on the basis of optical properties and to examine relationships between these characteristics and other properties of the humus layers.
Optical properties of HA were determined from humus layers of forest ecosystems on dry, moist, wet (seepage) and very wet habitats in both dry and wet subzones of the Coastal western hemlock zone. Color intensity of HA solutions was found to increase with an increasing moisture in both subzones. In the wet subzone, however, optical properties showed relatively less variation, indicating similar conditions of humus formation. Strong color of HA solutions was attributed to the development of mature HA, which are more easily decomposable and exhibit greater microbiological activity.
Color intensity of HA solution showed some relationship to major humus forms (mor, moder and mull), but one that may be obscured by the stand tree species composition. Similar relationships were found between color intensity of HA and tree species from which litter humic acids develop. The results suggest that western redcedar and Douglas-fir have amelioration effect on humus layers in this respect.
Significant correlations were found between optical properties of HA and several chemical properties of humus layers. Their relationship to carbon/nitrogen ratio is of particular interest in that it tends to confirm earlier reported direct correlations.
It was concluded that optical properties of HA alone are not sufficient to separate between humus layers of the ecosystems studied. However, in combination with other characteristics and in relation to forest ecosystems they are useful in assessing the quality of HA and the conditions influencing their formation.
Detailed Infonnation on this subject may be obtained by writing to the Infonnation Division, B.C. Forest Service, Legislative Buildings, Victoria B.C. V8V 1X5 for Research Note No. 76 by K. Klinka and L.E. Lowe titled, "Organic Constituents of Forest Humus Layers in the Coastal Western Hemlock Biogeoclimatic Zone of British Columbia in Relation to Forest Ecosystems."
[Abstract contains full text of memo.]
BC Forest Service - Research Division. 1976. Organic constituents of forest humus layer in the Coastal western hemlock biogeoclimatic zone of British Columbia in relation to forest ecosystems. 3. Optical properties of humic acid fractions.. British Columbia Ministry of Forests, Lands, Natural Resource Operations and Rural Development. Research Memo (FLNRORD). RM9
Topic: FLNRORD Research Program
Keywords: FLNRORD, Research Memo, British Columbia
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