Soil moisture- and texture-dependent effects of soil deposition on evaporation and carbon emission

Abstract

Soil erosion drives water and nutrient redistribution among landscape positions and thus global biogeochemical cycles. However, large uncertainties remain in the effects of deposition after erosion on soil hydrological and nutrient turnover, hindering precise assessment of global water and nutrient budgets. Herein, we presented the results of soil evaporation and carbon (C) emission measurements in a 19-day simulated depositional experiment at standard temperature (25 °C). A homogeneous soil treatment was designed as a control to assess the effects of deposition. Three soils (Ultisol, Mollisol and Entisol) varying in texture and organic matter content were used, and two soil moisture conditions (drying and wetting) were included to examine the interactions of soil texture and moisture with deposition. Soil macropores were measured using X-ray tomography at the end of the simulation experiment to relate the soil structure to evaporation and C emission. We hypothesized that the deposition of soil after erosion will increase evaporation and C emission and that such effects are regulated by the soil texture and moisture conditions. The depositional soils had greater macropore numbers (8/cm3), macroporosity (0.61 %/cm3), connectivity density (0.91/cm3), cumulative evaporation (332.92 g) and C emission (2.46 g kg−1) than the homogeneous soils (1/cm3, 0.05 %/cm3, 0.02/cm3, 303.35 g, and 1.95 g kg−1, respectively). The effect of deposition on macropores was greater under drying condition than under wetting condition and was greater in the Mollisol than in the Ultisol and Entisol. The effects of deposition on evaporation dynamics varied with soil moisture conditions regardless of soil texture, with less effect under drying condition but increased evaporation under wetting condition. The deposition increased C emission under both drying and wetting conditions for the Ultisol and Entisol, but its impact on the Mollisol varied with the soil moisture treatment, with increased C emission under drying condition but decreased C emission under wetting condition. These results suggested that the effects of deposition are regulated by the soil texture and moisture and that the development of macropores due to shrinkage in depositional soils increased soil water loss and carbon decomposition, which might decrease C sequestration potential in deposition sites.