Influence of drainage amelioration on the heavy metal content of floodplain soils in the middle Amur lowland

The features of floodplain soils of small rivers depend on frequently changing environmental conditions (e.g., volatile humidity, vegetative composition, dynamics of alluvial sediment deposits and terrain features). Research on floodplain soils is important for regions characterized by agricultural land and for those with waterlogged soils in which drainage and reclamation works are conducted. For example, Leninsky District of Jewish Autonomous Oblast is characterized by farmlands, which occupy approximately 30% of the total territory. Our research aims to study the influence of amelioration on heavy metal (HM) content of floodplain soils in the middle Amur lowland. The agricultural land of Leninsky district is mainly represented by meadow clay soils formed on heavy textured parent material characterized by low-power humus horizon. The presence of slopes and alluvial clay impedes the flow of surface water and groundwater. These factors result in the retention of a significant amount of moisture in the soil. Soil water retention restricts the usage of water without requiring reclamation. This research focuses on enhanced and unenhanced polygons and reclaimed, tilled and untilled agricultural turnover in soil. We took samples from the soil surface in accordance with GOST 28168-89 in the spring and autumn of 2009-2011. The HMs Fe and Mn are typical natural pollutants in the middle Amur Lowland, whereas Ni, Cu, Pb, Zn, and Co are typical natural and anthropogenic contaminants. HMs are mobilized in the soil when extracted with 1 N hydrochloric acid. We analyzed HM contents using atomic absorption spectrometry (Thermo Electron SOLAAR 6M). Our study indicates that the accumulation of HM during the growing season depends on the land use type and weather conditions. Thus, the lowest HM concentrations were determined in reclaimed soils during their periodic flooding in spring and autumn (2009). Relative to 2009, the years with lower atmospheric moisture (2010-2011) yielded considerable amounts of HM. In 2009, the largest total contamination score in drained soil belonged to the first pollution category, i.e., the "allowable" category, and the rest of the soils belonged to the second category. We observed an increase in soil contamination, categorized as "highly dangerous", during the period of low precipitation volume (2010-2011). Thus, drainage and reclamation reduce the content of mobile forms of HM and are better used in soils with agricultural crop rotation than in unenhanced soil. The article contains 1 figure, 2 tables, 21 ref.

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