The Morphology,Composition, And Formation Environment Of Soil Fe-Mn New Growth In Different Landscape Sites

The Fe-Mn new growth is an important component in soils.Its morphology,structure and composition are products of pedogenesis,and can be a reflection of soil formation time and environmental changes.Currently,there are many studies on Fe-Mn nodules and Fe-Mn films.It is believed that soil iron and manganese nodules were formed under the condition of groundwater fluctuation,mainly occurred in low plains and depressions.However,iron and manganese nodules also can be found at a stable upland in Shenyang area,and the origin has not been clearly addressed.In this paper,investigated series profiles of soil were from three different landscape sites.They are Tianzhushan and Xiushuihe in Shenyang,Shuiyuan in Yingkou.By means of soil morphology,soil geochemistry and soil mineralogy,the distribution,morphology and geochemical elements of the soil Fe-Mn new growth are studied,and its formation environment and formation mechanism are discussed.The result can provide a scientific basis for further understanding the distribution regularity,formation mechanism and environmental significance of Fe-Mn new growth in soil.Some meaningful results were listed as follows.?1?Different landscape sites have different kinds of Fe-Mn new growth.The tubular Fe-Mn new growth was found in the low-lying area of the edge of the river and lake.The water level of the area is shallow,even have the seasonal water surface,and the aquatic plants such as reed and calamus grow.With the elevation of the terrain and the change of vegetation types,there is no tubular Fe-Mn new growth,but Fe-Mn nodules appeared.Fe-Mn nodules appear at different landscape parts,such as low level land,stable upland and the slope surface between them.In low level,groundwater level is shallow,the wet vegetation is growing.The groundwater level in the slope surface and stable upland are deep,the vegetation is mainly mesophyte,and now most of them are cultivated as farmland.The results further indicate that the number of Fe-Mn nodules in soil under the landscape of stable upland is the largest,which is 42.34g/kg,followed by the foot of slope,while the number of Fe-Mn nodules in the middle part of the slope is the least,which is 13.69g/kg.?2?The order of the major element content in the soil was SiO₂>Al₂O₃>K₂O>Fe₂O₃>CaO>Na₂O>MgO>TiO₂>MnO>P₂O₅.With the increase of topography,the content of SiO₂ increased,and the content of Fe₂O₃ and Al₂O₃ decreased,There was no significant change in MnO;The total chemical composition of the tabulate Fe-Mn new growth is similar to the Fe-Mn nodules with SiO₂,Al₂O₃,and Fe₂O₃ as the major component.Minerals are mainly quartz and feldspar.Most of free iron oxide in tubulate Fe-Mn new growth was crystalline iron oxide.The content of different iron oxides in tubulate Fe-Mn new growth was greater than that in the soil.Most of manganese oxides were free manganese in tubulate Fe-Mn new growth and most of free manganese oxide was in crystalline manganese oxide.Free degree of iron was lesser than that of manganese in tubulate Fe-Mn new growth.The activity of manganese in tubulate Fe-Mn new growth was lesser than that in the soil.?3?The formation of Fe-Mn new growth in different forms is controlled by soil moisture,which can create different soils redox conditions.The groundwater level in the stable upland area of Shenyang is deep.The freezing thawing appears alternately in early spring,and results in existence of an impermeable layer in the soil,which creates an alternately oxidizing and redox environment for the formation of soil Fe-Mn nodules.In addition to the alternation of freezing thawing and thawing in early spring,the low level soil also has the effect of groundwater,which is influenced by the fluctuation of the groundwater level in different seasons.The oxidation and reduction of soil is alternately carried out,which is beneficial to the formation of Fe-Mn nodules.In low-lying landscape,the soil is waterlogging and the soil condition is waterlogging reduction.However,the oxygen secretion of aquatic plants root causes oxidative environment around the roots.A large number of iron and manganese oxides are deposited on quartz,feldspar and other minerals around the roots.After root death,the root decays and the hollow brown tubular Fe-Mn new growth is retained in the soil.The tubular Fe-Mn new growth can reflect environmental changes and can be used to interpret paleoenvironment.