FOREST PEATLAND DRAINAGE AND SUBSIDENCE AFFECT SOIL-WATER RETENTION AND TRANSPORT-PROPERTIES IN AN ALBERTA PEATLAND

Water table level control by drainage improves forested peatland sites for tree growth, but can also result in subsidence of the peatland su rface. The purpose of this study was to investigate the effects of cha nges to peat bulk density associated with postdrainage subsidence on p eat hydrologic properties at a peatland drained for forestry in north- central Alberta, Canada. Feat hydrologic functions were deter mined by inverse techniques developed for multistep outflow experiments (MULST P). Se, cn years after drainage, mean peat bulk density (0-40-cm depth ) was 63% greater and mean soil water retention (-5 to -15000 cm press ure head) was 66% greater than pear from the nearby undrained control area. Subsidence after drainage was associated with loss of pores >600 -mu m diam. with concurrent increases in 3- to 30-mm-diam. pore-size c lasses, Mean saturated hydraulic conductivity was 1.69 and 14.46 cm h( -1), while mean unsaturated hydraulic conductivity (-5 to -15 000 rm p ressure head) was 0.014 and 0.001 cm h(-1) in peat from drained and un drained areas, respectively. Changes in water transport characteristic s and in the pool of ''plant-available'' soil water will probably be b eneficial to tree growth in the drained area.