<Fig. 6>
The probability maps for the increases/decreases in SOC over the three time periods were calculated based on the SGS-generated SOC realizations (Text S1 and Fig. 6). During 1980-2000, the areas with significant SOC increases were mainly distributed throughout the study area, except for several areas (green regions in Fig. 6a) scattered around Taihu Lake. However, from 2000-2015, the probabilities of SOC increase in most areas were less than 0.40, while the areas with higher probabilities (0.50-0.70) of SOC increase were mainly distributed in the western parts and the northeastern corner of the study area (Fig. 6b). Over the entire 35-year period (1980-2015), the areas with significantly increased SOC were identified in the western and northeastern parts near the Yangtze River (Fig. 6c). However, for the probability of SOC decreases (Fig. 6d-f), a high probability of SOC decreases over the period of 2000-2015 in the southeastern parts of the study area can be intuitively observed. Over the entire 35-year period (1980-2015), the areas with significantly decreased SOC appeared to be very limited and were mainly located in northwestern Kunshan city.
Based on the uncertainty intervals of the changes in SOC (Fig. 7), the average area percentages of the decreases in SOC over the periods of 1980-2000, 2000-2015, and 1980-2015 were estimated at 21%, 62%, and 40%, respectively. This global information on the area proportions of the SOC changes across the study area implied that the SOC changes went through two distinct stages: SOC increases were predominant over the first two decades (the SOC for 79% of the study area increased during 1980-2000, Fig. 7, left) while SOC decreases became predominant in the subsequent 15 years (the SOC for 62% of the study area decreased during 2000-2015, Fig. 7, middle). However, over the entire 35-year period (1980-2015), the SOC for 60% of the study area increased (Fig. 7, right), indicating an overall trend of SOC accumulation in the area.