The hydrological cycle in the ravine oak forests of steppe Prydniprovia

Abstract

The characteristic of the hydrological cycle in the ravine oak forest is given in the work. In its preparation, we proceeded from assumption about the participation of groundwater in water feeding of wood vegetation. To confirm or refute this the term average groundwater depth, the changes in its long-term, seasonal and intraday level dynamics were analyzed. The intra-annual structure of the groundwater regime was established, while in the structure the three specific periods were identified – winter-spring recovery, spring-autumn recession and autumn recovery. It was established that the duration of the hydrological year between the beginning of winter-spring recovery and the ending of autumn recovery was about 11.5 months.  Most often, the hydrological year flows between January and December of neighboring hydrological years. The groundwater depth during the observation period ranged from 7.65 to 10.08 m from the surface. The amplitude of level changes between seasons was 0.57–1.59 m. The speed of rise and fall level was set, while the instability of characterized indicators was observed, that is closely related to the temperature of atmospheric air of the previous period. The annual dynamics of groundwater level is compensatory in nature, in which the spring-autumn recession is compensated autumn and winter-spring recovery. From the position of winter minimum level and the deviation of the average annual rainfall norms, it was found that the course of the annual changes level has a close correlation with the amount of precipitation. Intraday dynamics of level conditions during the vegetation period has stepwise, descending character, which means that there is no direct connection of groundwater with woody vegetation. It was found that at the absence of available groundwater, the incoming part of the water balance was determined by the vegetation period precipitation and the moisture contained in the soil at the beginning of the vegetation period. The amount of precipitation of the vegetation period, excluding precipitation detained by the cover and litter, during the observation period was over 292 mm. Dynamics of soil moisture  in 1.5 meters layer showed that the most dynamic changes in moisture took place in the upper meter of soil. During the non-growing period in the 1.5 meters layer up to 252 mm of moisture is accumulated. The total amount of rainfall and soil moisture in the 1.5 meters layer of soil at the beginning of vegetative period averages 542 mm, 46 % of which is soil moisture, and the remaining 54 % is the precipitation moisture. The average annual evapotranspiration coefficient is calculated from the ratio of the amount of soil moisture at the beginning of the vegetative period and all vegetative period precipitation to evapotranspiration of appropriate period of time. In this approach the figure for ravined oak forests is 0.78, 0.63 – for steppe plots of virgin land. The general moisture conditions prevailing here are local, are formed under the influence of geomorphological features on the background of climatic conditions and are responsible to the intrazonal type.