<Fig. 4>
The spatial distribution maps of the SOC contents derived by the OK
method were presented in Fig. 4, with a kriging error range of 1.16-3.67
g kg-1, 1.11-4.41 g kg-1, and
1.57-2.29 g kg-1 for SOC1980,
SOC2000, and SOC2015, respectively
(Figure S2). Overall, the SOC distribution patterns on the three
sampling dates were similar, with high SOC contents in the southeast
(mainly surrounding Taihu Lake) and low SOC contents in other parts of
the study area. However, differences in the local details of the spatial
patterns of SOC still existed among the three sampling dates. The
high-value areas with SOC1980 exceeding 18 g
kg-1 were mainly distributed in the southeast of the
study area, while the low-value areas with SOC1980< 10 g kg-1 were scattered along the
southern side of the Yangtze River and the areas near the western
boundary of the study area. The SOC1980 in most parts of
the study area ranged from 10 to 18 g kg-1. However,
in 2000, the high-value areas with SOC > 18 g
kg-1 expanded significantly across the study area;
these areas were located throughout the whole southeastern parts of the
study area and in several small areas in Jiangyin, Yixing, and Jintan
city. The areas with moderate values of SOC2000 between
10-18 g kg-1 were observed in the northwest (Dantu,
Danyan), in the southwest (Liyang, Jintan), and near the Yangtze River
(Zhangjiagang, Taicang). In 2015, the SOC contents in most parts of the
study area varied from 10 g kg-1 to 18 g
kg-1, while the high-value areas with
SOC2015 > 18 g kg-1 were
very limited and were only distributed in Yixing and southwestern
Changshu.
3.3 Temporal changes in SOC