There were no changes registered in methodology of the soil moisture monitoring in the year 2008. The Slovak side measures the soil moisture by a neutron probe up to a prescribed depth or to the depth of the ground water level. The Hungarian side measures the soil moisture with a capacity probe to the depth of 2 m. The soil moisture on both sides is expressed by the total soil moisture content in volume percentage recorded in 10 cm depth intervals for each measurement during the year. Measurements on the Slovak side were performed on 12 forest monitoring areas, on 5 biological monitoring areas and on 3 agricultural areas – Tab. 5-1. Measurements on the Hungarian side were performed on 6 forest monitoring areas and 8 agricultural areas – Tab. 5-2. The situation of observation objects is shown on Fig. 5-1.

Table 5-1: List of monitoring stations on the Slovak side

 Table 5-2: List of monitoring stations on the Hungarian side

* - new monitoring sites

5.2. Data presentation methods 

The soil moisture is presented in figures showing the average soil moisture content in volume percentage for the depth interval from 0 to 100 cm and from 110 to 200 cm. A small difference can occur in the Hungarian data, where the value for a depth interval under 110 cm can represent the average value from less than 10 measured values. On colour figures the soil moisture time distribution for the whole measured depth is presented at selected sampling sites. The graphical presentation of the whole set of measured data is given in the Slovak and Hungarian National Annual Reports. 

5.3. Evaluation of results on the Hungarian side 

In 2008 there were 15 soil moisture measurements done on the Hungarian side. Measurements continued at forestry monitoring sites in the floodplain area and at agricultural monitoring sites in the flood-protected area. Three monitoring sites at forest stands were abandoned, and three new monitoring sites on agricultural area was introduced into the data exchange in 2008 (Fig. 5-1). The moisture conditions of soils are essentially influenced by the rainfall conditions, by the soil layer thickness and its composition, as well as by the ground water level position.

The reason of slightly lower soil moisture content at the beginning of the vegetation period was the lack of precipitation in the winter period. However, higher water levels in November and December 2007 moisturized well the lower part of soil profiles, which created a good base. The higher amount of precipitation at the beginning of March partially replenished the moisture content in the upper layers as well. During April the soil moisture content was balanced, only at sites where the groundwater level decreased below the soil profile some decease of soil moisture content was registered as well. In May the soil moisture content decreased. During the rest of the vegetation period the soil moisture content of upper soil layers remained balanced thanks to more frequent and higher amount of precipitation. Decrease of the soil moisture content started at the end of August and lasted till end of the year. Significant decrease, especially in the depth interval from 0 to 1 m, was registered at the end of May, when the lowest values of soil moisture content were registered in the upper layer. Thanks to precipitation during June the soil moisture content increased and on most of observation site the highest soil moisture content were recorded, but at the end of June it decreased again. From the beginning of August the soil moisture content decreased and the decrease lasted till the end of October, when the lowest values of soil moisture content were registered in the layer between 1 and 2 m depth. At the end of the year only slight increase of soil moisture values was recorded. Generally it can be stated that the average soil moisture in 2008 was similar or slightly higher in comparison with the previous year.

The soil moisture on forestry monitoring sites

In general, the soil moisture content at all forestry monitoring areas was slightly higher in comparison with the previous year. This is valid for minimal and average soil moisture contents in the layer to one-meter depth. In case of maximal values lower values were recorded at monitoring sites T17, T18 and T20. At the beginning of the vegetation period the soil moisture content reached similar or higher values than in the previous year. Minimal values in the layer to one-meter depth were recorded during May, while the minimal values in the layer below one-meter depth occurred at the beginning of October. Maximal average soil moisture values in the layers up to 1-meter depth were recorded at the end of July. The ground water level all over the year moisturised the soil layers on monitoring site T15 (Fig. 5-3), on monitoring sites T16 and T18 it moisturized during increased discharges into the river branch system during May (Fig. 5-2, Fig. 5-4). Soil layers at monitoring site T17 and T19 were moisturized from the ground water level only in August. 

Table 5-3:  The minimal and maximal average soil moisture contents at forestry monitoring sites

The soil moisture on agricultural monitoring sites on the flood protected side

The soil moisture contents at monitoring sites T02, T04, T06 and T12 were mostly dependent on precipitation and weather condition. The ground water level influenced of the soil profile at monitoring site T10 and partially at monitoring sites T02, T04 and T12. The soil moisture content at monitoring site T06 in the year 2008 was influenced only by precipitation. The soil moisture values up to 1 m depth reached high values at the beginning of the year, but the highest values mostly occurred at the end of June and beginning of July. Average soil moisture values at the beginning of the year were mostly higher then the soil moisture values in the previous year. Minimal soil moisture values in both depth intervals were registered at the end of the year. The maximal average values in the soil layers below 1 m depth occurred at the end of June and beginning of July as in the upper layer. Minimal soil moisture values in the depth below 1 m depth were registered at the beginning of the year, but similar values were registered at the end of the year as well. The minimal, average and maximal values were in mostly higher in comparison with the previous year.

Monitoring sites T10 and T12 represent agricultural areas in the Middle and Lower Szigetköz. Both monitoring sites have a thick covering layer and throughout the vegetation period the ground water level moisturised the bottom part of soil layers.

Table 5-4:  The minimal and maximal average soil moisture contents at agricultural monitoring sites

 

5.4. Evaluation of results on the Slovak side 

Monitoring sites on the Slovak side are situated in the inundation area and flood-protected agricultural area (Fig. 5-1).

The soil moisture development at monitoring sites situated in the agricultural area (sites No. 2716, 2717, 2718) is stable during the whole observation period. No significant change can be observed in the soil moisture content and the position and fluctuation of ground water levels (Fig. 5-5). In the year 2008 the ground water level at monitoring site No. 2716 fluctuated in depths of 3-4 m, at site No. 2717 in depths of 2.5-3.4 m and at site No. 2718 in depths of 2.2-3 m.

The fluctuation of soil moisture content in the depth interval from 0 to 1 m entirely depends on climatic conditions and it was so in the year 2008 as well. In the depth from 1 to 2 m, the soil moisture fluctuation is partly influenced by the ground water level, at monitoring area No. 2716 occasionally. The average soil moisture content in the depth up to 1 m in the year 2008 fluctuated in the range from 8 to 22 % at monitoring site No. 2716, in the range from 25 to 35 % at monitoring site No. 2717 and in the range from 25 to 36 % at monitoring site No. 2718. Comparing these values with the previous year it can be stated that the soil moisture content in 2007 was slightly lower, especially in the layer up to 1 m depth. The soil moisture content was supplied during the winter period and especially during rainfalls in March. In April the soil moisture content started to decrease and the minimal values occurred from May to September. Slight recharge occurred during July, when the precipitation amount significantly exceeded the long-term average value. Maximal values were registered in January 2008, while the minimum values occurred from June to October. In the depth between 1 and 2 m, the soil moisture content mainly varied from 16 to 22 % at monitoring site No. 2716, in the range from 31 to 38 % at monitoring site No. 2717 and in the range from 13 to 28 % at monitoring site No. 2718. Contrary to the upper layer the minimum values were recorded from September till end of the year 2008. The maximal values were registered in April and May, when the increased amount of water was discharged into the inundation area. 

Table 5-5:  The minimal and maximal average soil moisture contents at agricultural monitoring sites

The soil moisture in the inundation area, along with the ground water level and precipitation, is highly dependent on natural or artificial floods. In the hydrological year 2008 no natural flood occurred. The highest discharge wave reached 4780 m³s^-1, which means that the inundation area was flooded only partially, mainly in the lower part. The soil moisture content at the beginning of the year was rather high. In the depth interval from 0 to 1 m thanks to the recharge from ground water level in November and December 2007 and thanks to high precipitation amount in the second half of January and in the first half of March the soil moisture content on most of the observed sites reached maximum average value. At some observed sites (monitoring areas No. 2706, 2755, 2758, 2760, 3804 and 3805) high values were recorded in June and July as well, during higher discharges in the Danube. The lowest values in the layer down to 1 m depth were mostly recorded in September and October. The lowest values in the depth interval from 1 to 2 m were registered almost exclusively at the end of the year, in October and November or December. The maximal values, depending on the position of the monitoring site, occurred during the increased discharge into the river branch system in May and June, or during discharge waves on the Danube in July and August. Due to low water level in the Danube during last months of the year the soil moisture content at the end of the year was significantly lower in comparison with the starting content at the beginning of the year. Concerning the minimal and the maximal values it can be generally stated that values were slightly higher in comparison with the previous year at almost every monitoring site in both depth interval.

The thickness of soil profile at monitoring sites No. 2703, 2764, 2763, 2762 and 2761 in the upper part of the inundation area is low, similarly to the Hungarian side. The ground water level at these places fluctuates in the gravel layer only. In 2008 the ground water level on area No. 2703 fluctuated from 3.8 to 5 m, on the areas No. 2764, 2763, 2762 and 2761 changed from 1.2-5.0 m. Layers to 1 m depth were highly dependent on climatic conditions, however the increased discharge in the Danube in August had a great influence as well (Fig. 5-7). Layers below 1 m depth were strongly influenced also by the ground water at the time of increased discharge into the river branch system in May-June. Maximal average soil moisture contents occurred during first months of the year. Minimal values occurred during autumn (mostly September and October).

The thickness of the soil profile in the middle part of the inundation area is higher. In general the ground water regime in this region is influenced by the water supply of the river branch system, introduced in May 1993. Moreover, the natural or artificial floods have significant influence on the ground water level. The ground water level in 2008 fluctuated above the boundary between the soil profile and gravel layers - monitoring sites No. 2704, 2705, 2758, 2759, 2760 (Fig. 5-6a, Fig. 5-6b, Fig. 5-8) and supplied the soils with water during first half of the year. The maximal values of average soil moisture content in the layer to 1 m depth were reached in March and July 2008, minimal values occurred mostly in September 2008. In the layer below 1 m depth the maximal values occurred in June and July; the minimal values at the end of the year 2008.

Table 5-6:  The minimal and maximal average soil moisture contents at forestry monitoring sites

In the lower part of the inundation area, downstream of the confluence of the river branch system and the Danube (monitoring sites No. 2706, 2756, 2755), the ground water level usually fluctuates around the boundary between the soil profile and the gravel layer. Since the discharges in the Danube in the year 2008 were rather low the groundwater level moisturised only the deeper part of the soil profile. Monitoring sites were not flooded. Due to riverbed erosion the ground water level fluctuated in the depth below 1 and 2.5 m. The soil moisture in the upper layer in 2008 was exclusively dependent on precipitation. Significant refill occurred in March, partially during June and July as well, however since August continuous decrease of soil moisture was characteristic till the end of the year. The minimum and maximum values were related to the minimum and maximum ground water levels respectively. Minimal average values of soil moisture in layers up to 1 m depth occurred in September and October, in the layer below 1 m depth in November and December. The maximal average values of soil moisture were reached after the discharge waves in March and August (Fig. 5-9a, Fig. 5-9b).

The soil moisture contents at monitoring sites No. 2707, 3804, 3805, located in the inundation below the confluence of the tailrace canal and the Danube old riverbed, are highly influenced by the flow rate regime in the Danube. The maximum values in 2008, in the depths up to 1 m and between 1 and 2 m, occurred in March, June and August, while the minimum values occurred at the end of the year (October-December). The ground water level at monitoring sites No. 2707, 3804 and 3805 fluctuated in the depth 1.2-4.5 m. The riverbed erosion negatively influences these monitoring areas. During low flow rates in the Danube the ground water level does not supply the soil profiles sufficiently.