Characterizing organic matter and nutrient status in smelter-affected soils
Forest vegetation dieback has occurred around Flin Flon, Manitoba and Creighton, Saskatchewan since the beginning of the 20th century, when sulphide ore smelting began in the area. In order to support future revegetation strategies, evaluation of soil organic matter (SOM) quality and quantity and soil nutrient status variation in the area is necessary. This study focused on the spatial variation of SOM and soil nutrient status, particularly in relation to percentage plant (ground and woody species) cover. Soil nutrient status and other soil properties were also evaluated based on direction around the smelter. To identify spatial variation of SOM and soil nutrient properties, two 3-km transects were established North and South of the smelting stack and soil samples were collected every 100 m. To identify variation in soil nutrients and other properties based on direction around the smelter, eight 200-m by 200-m grids were established at each cardinal and ordinal direction, 3-km from the smelter. Soils were classified as mineral or organic, and percentage ground species and woody species cover was measured at each sample point. Transect samples were analyzed for SOM fractions including light fraction (LF) weight, LF and heavy faction (HF) carbon (C) and nitrogen (N) content, water extractable organic carbon (WEOC) and total dissolved nitrogen (TDN). Whole soil samples from the transects and grids were analyzed for total organic C (TOC), total N (TN) and total sulphur (TS), as well as exchangeable cations, cation exchange capacity, base saturation, pH and clay content. Transect data was analyzed with non-metric multidimensional scaling and ordination to determine significant variables related to percentage ground and woody cover and/or distance from the smelter, for mineral and organic soils separately. Differences in soil characteristics between grids were identified using Kruskal-Wallis analysis of distribution and the median test of independent samples. Results varied depending on mineral or organic soil classification. Percentage ground and woody species cover ranged from 0% to 90%. Light fraction and HF results were within a range seen in previous boreal forest studies and had median C to N of ~ 30 – 45 and ~20 - 30 for LF and HF, respectively. Low values of WEOC (mineral soil median between ~ 2 to 5 mg C kg-1 soil; organic soil median between ~ 28 to 60 mg C kg-1 soil) and TDN (mineral soil median between ~ 0.4 to 1 mg N kg-1 soil; organic soil median between ~ 4 to 9 mg N kg-1 soil) were identified. Non-metric multidimensional scaling and ordinations indicated the significant variables related to plant cover varied between mineral and organic soils. In mineral soils, cation and cation exchange variables were most significantly (P = 0.001) correlated to ordinations; however, percentage ground species and woody species cover vectors grouped with SOM quality and quantity vectors (LF-C:N, HF-C:N, LF-N and TDN) indicating SOM variables are more related to plant cover than other variables analyzed. In organic soils, trends were less obvious and may be masked by the intrinsic pedologic properties that define organic soils. Areas with low plant cover had lower SOM C:N and higher TN, likely attributed to more decomposed (recalcitrant) SOM. Total nutrient status of whole soils did not effectively explain inconsistent vegetation cover; and exchangeable cation content, cation exchange capacity and base saturation may reflect other disturbances. The soil issues hindering revegetation in the area are complex and multi-faceted; however when planning revegetation strategies in the area it is suggested using LF, WEOC and TDN SOM fractions to identify SOM quality and quantity variation.
Soil, soil organic matter, smelter, forest dieback, carbon, nitrogen, soil quality.
Master of Science (M.Sc.)