The study area is located south of northeast China. The study area is characterized by an
overall topography that decreases gradually from northeast to southwest and an average
ground elevation of 35–50 m. The study area is subject to a temperate monsoon climate, and
has an average annual temperature of 6.2–9.7 °C. The eastern portion of the area has a hilly
topography, while other areas are covered by Quaternary loose deposits. Quaternary deposits
gradually thicken from east to west, and the sediment particles gradually transition to coarse
sand from gravel, and then to medium and finally fine sand. Regional surface water bodies
include the Hun River, which runs through the study area from northeast to southwest, with
areas northwest and southeast of the study area containing a sewage river and sewage
irrigation channels. Land use and the sampling point distribution are shown in Fig. 1, while
Table 1 shows the fertilizer usage for the study area in 2011.