USING CS-137 TO INVESTIGATE NET SOIL-EROSION AT 2 SOIL BENCHMARK SITES IN QUEBEC

Cs-137 in the soil was used to estimate soil erosion at two National S oil Conservation Program benchmark sites in the province of Quebec (si tes 15-QU and 16-QU). The Cs-137 baseline in an uneroded forest area w as approximately 3100 Bq m-2. The Cs-137 content at site 15-QU ranged from 1072 Bq m-2 to 6389 Bq m-2, while at site 16-QU it ranged from 66 3 Bq m-2 to 5444 Bq m-2. Computed net erosion over the past 30 yr at s ite 15-QU varied from a loss of 9.65 kg m-2 yr-1 to a gain of 10.88 kg m-2 yr-1 and at site 16-QU from a loss of 6.38 kg m-2 yr-1 to a gain of 1.73 kg m-2 yr-1. The average net erosion rates were 2.43 kg m-2 yr -1 at site 15-QU and 1.29 kg m-2 yr-1 at site 16-QU. Soil samples coll ected on a grid pattern indicated that 90% and 83% of the area at site s 15-QU and 16-QU, respectively, was subjected to net soil loss. A com parison of total Cs-137 movement from eroded areas to depositional are as showed that 24.2% of Cs-137 was lost from site 15-QU, while about 1 7.6% of Cs-137 was lost from site 16-QU. Mapping of Cs-137 content and calculated soil loss and deposition showed that soil erosion was clos ely related to topography. Under similar slope conditions, the soil er osion rates were 27-68% higher at site 15-QU than at site 16-QU. Highe r tillage frequency and use of silage com were the suggested reasons f or the higher soil erosion rates at site 15-QU compared with site 16-Q U, which had been used for hay and small grains.