Net Nitrogen Mineralization in Natural and Drained Fen Peatlands in Alberta, Canada

Abstract

Abstract The lowering of water tables by ditching in boreal, minerotrophic peatlands modifies soil environmental factors that regulate nitrogen mineralization‐immobilization. Long‐term responses of nitrogen mineralization to drainage may vary depending on substrate pH and chemical composition. Research has shown that peat drainage and N fertilization of boreal Histosols increase growth rates of coniferous trees. This study was conducted to determine the response of N mineralization to lowering of water tables and to relate N mineralization to selected soil properties. Net N mineralization rates were determined by in situ incubation of peat samples in paired natural and drained areas of midcontinental boreal fens representing a gradient in soil pH from 4.0 to 7.2. Analysis of variance of N mineralization revealed a significant interaction between soil pH and drainage category. At pH 4.0, net N mineralization did not differ between the natural and drained areas. At the intermediate pH levels, net N mineralization in the natural areas was up to two times that of the drained areas. At pH 7.2, the N mineralization relationship between the two areas was reversed. Post‐ditching increases in peat bulk density in the sites of intermediate pH correlated with higher volumetric water content and lower concentration of inorganic N compared with the natural areas. The concentration of inorganic N decreased by about 50% with soil depth to 30 cm in both the natural and drained areas. Although small for all soils, net NO − 3 production was not influenced by the pH level or drainage category from 7 to 30 yr after ditching.