| Summary: | <p> The goal of the study is to establish the contribution of geochemical systems, from sedimentary structures of southern Moldavian<br />Plateau, in triggering and evolution of gully processes. In this purpose, a case study has been<br />carried out on Ivesti gully, in which, the textural and geochemical properties of original<br />subsurface structures had been analyzed. The site is 650 meters long and approximately 35<br />meters wide located east to Ivesti village along the DN11A road. The analyses where based<br />on 32 samples taken from along the gully and from four control section in order to ensure a<br />better cover. The contribution of geochemical processes in gully formation it refers to<br />alteration of hydrophisycal and mechanical properties of subsurface deposits, when a<br />salinization process is taking place and those deposits contain over 10% sodium ions in<br />cationic exchange capacity. These characteristics lead to a water holding pressure in clay<br />minerals over 140 atm., which determine the beginning of deposits mobility. In this case, the<br />salinization process is not present; the soluble salts concentration is between 17 and 116<br />mg/100g soil and 205 – 217 salts mg/100g soil along median line of right bluff, downstream<br />from active gully processes. None of the control section contains deposits in saline class. The<br />general ionic formula of soluble salts contained in surface deposits is Ca-Mg-Na-K-NH4,<br />respectively SO4-HCO3-Cl-NO3 alternating with HCO3-SO4-Cl-NO3. The preliminary data<br />regarding the chemistry of sodium, potassium, chlorine, sulfates and hydrogencarbonates<br />shows that in actual deposits, the salts of these ions do not reach the values to start the<br />chemical suffusion processes. In this gully, the most important factor is the nature of the<br />bedrock - a weak cohesive material which allows breaking of the kinetic equilibrium of the<br />slopes (7,5-8°). The process is amplified by the hydrological characteristics of the region. In<br />these conditions, the viscosity of the bedrock decreases and the sand is transported exclusively<br />because of gravitational attraction. In the main section, but especially in the secondary gullies<br />located on the right side of the main section, chemical suffusion processes might be present in<br />the early stages of the gully development, because of the primary salinization of the deposits,<br />now levigated. Also, between other factors that contribute on gully development, its worth to<br />be mentioned the climatic particularities of the entire area, especially precipitation regime, the<br />land use represented by vineyard plantations and the existence of pluvial flow rills from<br />slopes, which can contribute to evolution of actual active processes.</p>
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