The influence of extreme meteorological phenomena on soil water regime of lowlands Institute of Hydrology - Slovak Academy of Sciences Bratislava, Slovak Republic Vlasta Štekauerová - Viliam Nagy Obervellach, 2007

Introduction

The amount of water in soil represents a water resource for the land biosphere. This resource is closely related to the hydrological cycle on the Earth, and is under a constant influence of the slow global changes and the anthropogenic activities. For evaluation of the water storage in the soil aeration zone, there exists an objective method – the direct monitoring. Data on the water content in vertical of the unsaturated soil zone are acquired through this monitoring. Soil water storage dynamics represents an indicator of the natural environment, which helps to monitor the impact of human activities and of the slow changes of a global character. Extrapolation of time course of the water storage indicates the trends for future.

In some regions of Slovakia ever more some extreme events occur: 1.extreme flashy rainfall amounts 2.longer periods with minimum or even no rainfall extreme local flood no endurable drying up of the soils if it becomes fully developed, in many cases it ends as an irreversible process

The soil water regime describes the integral changes of water content in the unsaturated soil zone during a certain period. Long term monitoring of the water regime gives the possibility for classifying the soil types, and for fulfilling expectations of various research subjects, such as ecology, hydrology or agronomy. Soil water regime determines soil productive ability and depends on water inflow and outflow into or out of unsaturated soil zone. Soil water regime Unsaturated soil zone is one of the most important and complicate part evaluated water movement in hydrologic cycle

Soil surface Groungwater level The lower boundary is usually delimited by groundwater table The water supply in the unsaturated soil zone is directly influenced by a water transfer through its upper and lower boundary The upper boundary reacts directly on meteorological and climate conditions

In case of the water regime evaluation it is important to take into consideration the available amount of water from the soil for the plant in different ecosystems. Hydrolimit is the soil water content, reached under a certain condition  the value of the hydrolimit is different for plant species and varieties  hydrolimits are useful to calculate the water balance in a soil profile  or instance, to define the quantity of water available for or used by the plants FC Field capacity PDA Point of decreased availability WP Wilting point

To estimate evolution of water storage in localities near Danube in Slovak region impacted by Gabcíkovo power station 1 - agricultural cultivated localities with different influence of groundwater table - Báč and Čilížska Radvaň during 1999 – agricultural cultivated locality Báč and forest ecosystem Bodíky without influence of groundwater table during 1999 and The aim of presentation

Localities of the study area  Regions around the Danube - Žitný ostrov (Rye Island) are bordered by a natural water way called Little Danube.  The region is crossed by channels that regulate the groundwater level.  Along the river Danube the heterogeneity describes best the soils of the area which leads to heavily layered soil profiles.  Some parts of the region are under intensive agricultural use and some parts are covered by a forest ecosystem.

agricurtural cultivated soil forest ecosystem

The soil profiles are mutually very similar in Báč and Bodíky. The texture of the soil surface is mainly loam and it gradually turns to sandy-loam and sand downwards. The sand is passing into a gravelly subsoil in the deeper layers. The sand layer begins approximately at a depth of 120 cm in Bodíky and at cm in Báč. The soil profile in Báč is considerably more layered than in Bodíky. The levels of the groundwater tables are fluctuating only in the gravel subsoil in both localities and are therefore not influencing the water regime of the 0– 60 cm soil layers. The soil profile of Čilížska Radvaň is distinct than of Bač (the soil profiles in these both localities are agricultural cultivated). There is a clay-loam passing into loam, sand and gravel in the depth of 150 cm under soil surface and soil water regime is influenced by groundwater table during whole year.

Daily precipitation during years 1999 – 2004 measured by meteorological station Gabčíkovo (the data were obtained from Slovak Hydrometeorological Institute).

Average daily air temperature measured at the meteorological station in Gabčíkovo during years 1999 – 2004 (the data were obtained from Slovak Hydrometeorological Institute).

Method  Soil water contents were measured from the soil surface to the groundwater level at 10 cm intervals by neutron probe every two weeks (month in winter ).  Water storages of soil layers were calculated from the soil water contents monitored by the neutron probe.  Drying branches of the soil water retention curves were measured on the soil samples under laboratory conditions by overpressure apparatus (The soil Moisture Equipment, Santa Barbara)  They were approximated using the relation of van Genuchten.  The approximated soil water retention curves were used for establishing the hydrolimits as FC, PDA and WP.

Results and discusion

Agricultural cultivated localities with different influence of groundwater table - Báč and Čilížska Radvaň during 1999 – 2004

Time course of groundwater levels in localities Cilizska Radvan and Bac from 1999 to 2004

The course of soil water storages in the soil layer 0-30cm, 0-60cm and 0-80cm during years

The course of soil water storages in the soil layer 0-30cm, 0-60cm, and 0-80cm in Bac during years 1999 and 2003

The course of soil water storages in the soil layer 0-30cm, 0-60cm, and 0-80cm in Čilížska Radvaň during years 1999 and 2003

Agricultural cultivated locality Báč and forest ecosystem Bodíky without influence of groundwater table during 1999 and 2004

0 – 30 cm WP – wilting point Báč Bodíky

30 – 60 cm WP – wilting point Báč Bodíky

0 – 30 cm FC – field capacity PDA – point of decreased availability WP – wilting point Báč Bodíky 1999, 2000

30 – 60cm Báč Bodíky 1999, 2000 FC – field capacity PDA – point of decreased availability WP – wilting point

Conclusions

Soil water regime determines soil productive ability and depends on water inflow and outflow into or out of unsaturated soil zone. Unsaturated soil zone is one of the most important and complicate part evaluated water movement in hydrologic cycle. In case of the water regime evaluation it is important to take into consideration the available amount of water from the soil for the plant in different ecosystems and to estimate it by hydrolimits. During these six years were registered more of extreme meteorological events in region near Gabčíkovo in Slovakia.

From the tilled localities soil profile in Báč was not influenced by groundwater level or soil profile in Čiližská Radvaň was influenced by it. Soil profile in Čiližská Radvaň is better storage by water than soil profile in Báč. Soil profiles in Báč (tilled) and in Bodíky (forest ecosystem) were not influenced by groundwater level. The year 2000 was considerably dryer and warmer during vegetation period than Both localities responded on this phenomenon. The water storages of studied soil layers were lower in year 2000 than in The water storages in the root zone decreased in It could be concluded that the forest ecosystem is less susceptible to decrease in the integral water contents in the root zone as the tilled soil.

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