Effect of particle size distribution of sediments on development of polder soils in Japan

Purpose

Polder soils develop from oceanic and lacustrine sediments covered with seawater, brackish water, and freshwater after artificial drainage. Because there are several concerns regarding the agricultural use of polder soils, soil genesis and properties have been considerably surveyed, mainly focusing on problematic soils developed from fine sediments. Although sediments have a wide range of particle size distributions due to different sedimentary conditions, particle size of parent materials have not been well addressed to understand the soil developmental process. In this study, Japanese polders with different reclamation ages and sedimentary conditions were surveyed to clarify the soil formation process and factors affecting pedogenesis.

Materials and methods

Soil samples were collected from 15 soil profiles in six Japanese polders under different land use types. Sedimentary conditions of polders were evaluated from particle size distributions using the hydrodynamic classification proposed by Pejrup (The triangular diagram used for classification of estuarine sediments: a new approach. Tide-influenced Sediment Environ Facies, pp 289–300, 1988). The major soil-forming factors of polders were extracted by principal component analysis (PCA) using general soil properties.

Results and discussion

Brackish lake and inner bay polders were characterized by calm hydrodynamic conditions comprising fine particles. Two polders reclaimed from a shallow inland sea were characterized by violent hydrodynamic conditions. Sandy sediments were also characteristic of immature soils reclaimed from a freshwater lake and an estuarine tidal flat. Soils on polders developed under calm hydrodynamic conditions enabled the accumulation of high total carbon content. The soil-forming process in the brackish bay oxidized pyrite, leading to an acidic soil reaction. Conversely, soils developed from sandy sediments were characterized by low iron content. The PCA extracted two factors explained by particle size and soil reaction relating to acidification and salt leaching.

Conclusion

Polder soils can be mainly discriminated by their particle size distributions, which are characterized by hydrodynamics under the sedimentary conditions, and the polder soil development is affected by water management in land uses after artificial drainage.