Soil nutrient responses to increased snow pack in an alpine meadow

This study examined soil C, N, and P variation through the growing season and short-term responses of these nutrients to experimentally increased levels in snow pack in a formerly dry alpine meadow. Since 1993, a snow fence has been erected during the winter months in a dry alpine meadow at Niwot Ridge, Colorado, increasing the amount of winter snowpack. Samples were collected at regular intervals during the summer seasons of 1996 and 1997. Plot locations at three distances from the snow fence corresponded to deep, medium, and shallow winter snowdrift conditions. Soil samples were analyzed for NO₃−, NH₄+, P fractions, and total C, N, and P. Control plots were distance-matched to the treatment plots from the fence, but outside the influence of the fence.; Soil nutrient levels varied significantly through the growing season for all nutrients and nutrient fractions analyzed except the two most occluded P fractions. As expected, the plant-available nutrients had greater concentration variations and clearer growing season trends than the tighter bound nutrients. The P fractions had weak growing season trends that included a sharp increase in the more labile fractions with a corresponding sharp decrease in the more tightly bound fractions at the end of 1997. Total soil C, N, and P concentrations varied with location and exhibited a general decrease through the growing season, with C and N generally co-varying.; Only the plant-available soil nutrients of NO₃− , NH₄+, and resin P_i responded to the change in the snow regime with an increase in concentration. These nutrients had a threshold effect between the medium and shallow snow pack locations and demonstrated a stronger response to the change in snow regime earlier in the growing season. Total soil C and N concentrations decreased with shallower snowpack; however, this pattern was also present in the control samples indicating a background gradient. Changes in nutrient levels with a change in snow regime were already occurring in this formerly dry alpine meadow due to changes in plant community, temperature and moisture regime, and nutrient input with snow pack. These changes should increase and be more definite in the future.