Sources of uncertainty affecting soil organic carbon estimates in northern New York

Estimations of regional soil organic C (SOC) stores are sensitive to map scale effects, the geography of soil resources, and uncertainty stemming from SOC values assigned to soil series. This study assessed uncertainty associated with regional SOC estimation for the Tughill Plateau (Major Land Resource Area [MLRA 141]) of northern New York. Soil samples from 103 sites, representing 30 soil series mapped within the Tughill Plateau, were collected from the upper meter and analyzed to develop a series-specific SOC database. Four 24 km² subregions of the Plateau were identified and soil survey maps of four different scales ranging from 1:15 840 to 1:750 000 were compared. Soil survey maps were digitized, and their respective map unit compositions and areas were related to the series-specific SOC database to calculate SOC (weighted by land extent). Estimates using different survey map scales ranged from 16.6 to 17.6 kg C m^-2. Smaller-scale soil survey maps (1:250 000 and 1:750 000) produced SOC estimates that were greater significantly than the 16.7 kg C m^-2 estimated using the large-scale reference survey maps (1:15 840). Differences were caused by the process of map generalization, as soil series with lower mean SOC that occurred on the 1:15 840 survey maps were replaced by series that had higher SOC on the 1:250 000 and 1:750 000 survey maps. Although significantly different, area-weighted mean SOC estimates varied by <5%. The greatest uncertainty in regional SOC estimation originated from the variation in SOC values assigned to soil series, with coefficients of variation (CV) ranging from 3 to 87%.