Influence of Toposequence on Physical and Mineralogical Properties of Soils Developed on Basaltic Parent Material under Sub-humid Terrestrial Ecosystem
Abstract
Understanding of soil forming factors is crucial to define physical, mineralogical and morphological properties of soils. In addition to that soil formations were highly associated with slope positions which have influence on pedogenetic and weathering process of the soils. Because, topography or relief affects how water and other material are added to and removed from soils. The aim of this study is to enhance our understanding of the role toposequence in controlling chemical weathering, influence on physical and mineralogical properties in soils developed on basaltic parent material under sub-humid terrestrial ecosystem in Black Sea region of Turkey using geochemical and mineralogical data obtained from X-ray diffraction and Scanning Electron Microscope analysis. For this purpose, four representative profiles formed on different topographic positions of transect were investigated and designated according to Soil Survey Staff (2014)/IUSS Working Group WRB (2015) classification systems. The results clearly showed that topography strongly affects soil physical, mineralogical and morphological characteristics either directly or indirectly in the local region even soils formed on the same parent material with the same climatic condition. This case was also explained with chemical weathering indices (Chemical Index of Alteration and Chemical Index of Weathering) in this study.
- Introduction
Understanding of soil forming factors (e.g. parent material, climate, topography, vegetation and time) is crucial to define physical, mineralogical and morphological properties of soils. It is well known that the chemical and mineralogical composition and the physical structure of the parent material set the initial conditions of the incoming soil (Jenny 1941; Voortman 2011). Rolling topography is also another factor influence soil formation due to erosional losses, and affecting the distribution of vegetation (Florinsky & Kuryakova 1996; Sebastiá 2004), provides climatic conditions (Grzyl et al 2014; Ridolfi et al 2008). In addition, topography or relief is the most important factor for soil formation affects how water and energy were added and/or lost from soil (Dengiz & Başkan 2010). Arnold (2006) indicated that a reference relief unit was a catchment or watershed area and the analysis of lateral transfers on, in and through the soils had to be considered to understand the functioning of the landscape units. The systems could be open or close relative to the flow of water and energy. Therefore, Moore et al (1992) reported that correlations between quantified terrain attributes and measured soil attributes toposequence can be assessed.
Moreover, mineral weathering, fundamental part of pedological evaluation, also provides an essential role by transforming bedrock to weathered rock and consequently to soil that supply nutrients to ecosystems (Berner et al 1983; White & Brantley 1995; Dixon et al 2009; Lybrand & Rasmussen 2018; Tunçay et al 2019). In this case, during weathering, the elements are leached and accumulated in different ways due to several pedogenic processes that influence different elements and produce different results. These processes include dissolution of primary minerals, formation of secondary minerals, redox reactions, transportation of material and ion exchange (Middleburg et al 1988; Dengiz 2010). Therefore, it is important to understand how a soil is formed from bedrock and to examine how chemical or physical weathering influences the geochemical evolution of soils. As basalts locate a large part of the earth surface weathering, basalt formed by the solidification of molten materials that originated within the earth is important soil material global weathering and carbon cycling which covered a large part of the earth surface (Price et al 2005; Braun et al 2009; Heckman & Rasmussen 2011). When basalts weather in subhumid condition, a rapid loss of cations (Ca2+, Mg2+ , Na+ , K+ ) and relative accumulation of Si4+, Al3+ and Fe3+ that yield clay minerals develops (Eggleton et al 1987; Chorover et al 2004). Furthermore, many researchers indicated that the weathering of volcanic minerals is recognized to make a significant contribution to the global silicate cycle (Louvat & All`egre 1998; Dessert et al 2001; Kısakürek et al 2004), thus influencing carbon dioxide drawdown and climate control, since carbon dioxide is consumed particularly in Ca and Mg silicates weathering. For instance, on Deccan Traps in India, with an estimated area of 106 km2 , thought to account for 5% of the global silicate weathering flux (Gaillardet et al 1999). In total, basalt rocks may account for over 30% of the global carbon dioxide drawdown in silicate weathering (Dessert et al 2003).
There are many variables including geologic, climatic and topographic state that potentially affect chemical weathering rates in earth crust (Stallard & Edmond 1983; Grantham & Velbel 1988). Chemical weathering indices such as Chemical Index of Alteration (used for chemical weathering in sediment area) and Chemical Index of Weathering are used to define weathering profiles (Price & Verbal 2003). Changes in the weathering index with depth commonly are gradual or continuous, steady and systematic for homogeneous parent rocks (Sutton & Maynard 1992) reflecting continuous leaching of elements as weathering progresses on an initially homogenous parent material. Numerous studies have been conducted on determination the extent of weathering process, soil formation (Munroe et al 2006; Anderson et al 2007; Zhang et al 2007; Brantley 2008).
The purpose of this study is to further our understanding on the role toposequence on chemical weathering, along with its influence on physical and mineralogical properties in soils developed on basaltic parent material under sub humid terrestrial ecosystem in Black Sea region of Turkey using geochemical and mineralogical data obtained from X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) analysis.
Influence of Toposequence on Physical and Mineralogical Properties of Soils Developed on Basaltic Parent Material under Sub-humid Terrestrial Ecosystem
Tülay TUNÇAY Orhan DENGİZ Ali İMAMOĞLU
Year 2020, Volume 26, Issue 1, 104–116
