Impact of Hydroelectric Power Station "Iron Gate I" Backwater on Soil Wetness and Tree Diameter Increment in Flood Plain Forests on the Example of Profile ''Mlaca''

Marko Urosevic1, Renata Puzovic1, Milutin Stefanovic1, Aleksandar Drobnjak1

 

1 Institute for the Development of Water Resources Jaroslav Cerni, Jaroslava Černog 80, 11226 Pinosava-Belgrade, Serbia; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

Abstract

After the construction of the "Iron Gate" Hydroelectric Power Station (HPPIG), a great man made lake has been formed in the Danube and its tributaries. Areas between the river and the protection embankments along the flow of the Danube and its tributaries are floodplain forests called "foreland" and are usually covered with woods, mostly poplar and willow trees. The influence of the HPPIG backwater in period from 2014 to 2016 on soil moisture and growth of poplar Populus euramericana I-214 plantations in the vegetation period on the profile "Mlaca" is presented in this paper. The research shows that impact of the HPPIG backwater had caused serious deterioration of natural conditions in the foreland.

Keywords: backwater impact, flood plain forest, soil moisture, tree diameter increment.

Introduction

 

Large areas between the river and the protection embankments along the flow of the Danube and its tributaries the Sava, Tisza, Tamis and V. Morava, are referred to as "the foreland" and are usually covered with woods, mostly poplar and willow trees (Gavrilović Z. et al., 2010). The natural composition of tree species in floodplain forests along the Danube has been artificially changed during the last decades by the planting of non-native tree species, mainly establishing plantations of hybrid poplars (Marek S.).

Research work and studies on the impact of backwater on ecosystem changes along the Danube River and on the survival of forests in the flood plain forests – foreland, resulting from the construction of Hydroelectric Power Station ''Iron Gate I"(HPPIG), it is important to preserve the protective and economic functions of these forests.

Observations and research work, which had started in 1979 and lasted until 1990, are of great significance when reviewing the complex issues, as well as resolving the basic issues related to establishing the criteria for survival and cultivation of forests and forest cultures influenced by the "Iron Gate I" Hydroelectric Power Station (HPPIG).

This is the reason why observations and research work were reinstated in 2002, on two old and two new sites:

  • Danube River- profile Sibnica km 1158+000
  • Tamis River - profile Mlaca km 5+220
  • Danube River - profile Ivanovo km 1138 + 000
  • Danube River - profile Kovin km 1108 + 150

This paper will present the research findings of the influence of the ''Iron Gate I" Hydroelectric Power Station (HPPIG) backwater, on soil wetness and growth, and development of poplar Populus euramericana I-214 plantations on the "Mlaca" profile, during the three-year period of 2014-2016.

All observations and research works were carried out during the vegetation period (from April to October), except for the hydrological observations, which were carried out throughout the year.

 

The "Mlaca" Profile

The Mlaca profile is located on the left bank of the Tamis River, 5 + 220 km from the Danube, in a long narrow meander (Figure 1). Its meander is characterized by almost uniform relief shapes with relatively small deviations.

 

fig01
Figure 1: Profile "Mlaca" location.

 

The created micro relief has a decisive influence on the flow regime and groundwater regime, i.e., on the overall ecological conditions of the habitat. Due to the differences in the soil moisture regime, conditioned by the micro relief, the different habitats occur, from the lowest wetlands to the forests. Different plant communities, which are reduced to small areas, indicate habitat conditions, mainly the conditions of the land and the water regime in it. Most of the area on the "Mlaca" profile is covered with poplar cultures, and significantly less under autochthonous vegetation.

On the "Mlaca" profile there are two profiles which are being observed - profile P1 and profile P2 (Figure 2). Poplar trees on both profiles are of the same age (14 years) and planting density is 5 x 5 m.

 

fig02
Figure 2: Orto-photo image of the "Mlaca" profile with locations of observed profiles.

 

fig03
Figure 3: Poplar trees on profile P 1 (left) and profile P 2 (right).

 

tab01

 

Methodology

Research of the influence of the "Irong Gate I" Hydroelectric Power Station (HPPIG) backwater, on soil wettnes and the growth and development of poplar Populus euramericana I-214 plantations on the "Mlaca" profile included field work, laboratory measurements and software data processing.

Field work, on profiles P1 and P2, involved the opening of deep hydropodological profiles of up to 200 cm in a well for the purpose of determining the granulometric composition of the soil and taking soil samples to study the dynamics of capillary moisture in the soil., measurements of poplar tree diameters at breast height and the height of the poplar trees.

Granulometric composition is determined by combined piphet method, which involves the use of soil sieving and the piphet method (Tanja A., et al., 2009.).

 

Dynamics of Capillary Moisture in the Soil

Observations of moisture in the soil took place by method of soil sampling every 15 days at depths from 0,1; 0,3; 0,5; 1,0; 1,5 to 2 m or to the appearance of groundwater. Samples were taken in a disturbed form, during the vegetation period from April to October, using a hand drill, after which they were stored in small aluminum containers (Figure 4).

 

fig04
Figure 4: Aluminum containers for storing soil samples (left), manual drill for taking soil samples (right).

 

In laboratory conditions, we measured the content of hygroscopic moisture in the soil samples. First we measured the mass of the containers with the soil samples, the second step was to dry the samples in the electric kiln at 105°C to a constant weight. After that, the containers were washed and dried to measure the mass of the empty containers.

The difference in mass of the sample before and after drying it, is the loss of hygroscopic moisture. The calculation of the hygroscopic moisture content is based on the following formula (Tanja A., et al., 2009):

 

for01          (1)

 

Whig - hygroscopic moisture content

Mp - weight of the empty container with lid

Mpw - weight of the container with soil sample before drying

Mps - weight of the container with soil sample after drying

fig05
Figure 5: Electric kiln for drying soil samples.

 

Tree Diameter Increment

Tree diameter increment on the "Mlaca" profile was measured on thirty poplar trees Populus euramericana I-214, per profile. Measurements included measuring the breast diameters and heights. The observed poplar trees were marked with regular numbers (Figure 6).

 

fig06
Figure 6: Marked poplar trees (left), tree diameter measuring (right).

 

The formula for determining the volume of the observed trees is (Mirković D., 1993):

V = G · H · F (m3)          (2)

V - average volume of the observed trees

G - average diameter of the poplar trees per profile

H - height

F - volume coefficient

The sum of the circular cross-section (G) of the trees is obtained by measuring the diameters of all trees and the distribution of trees by thickness. The mean value of the height of the trees is obtained on the basis of height measurements on a few trees. The volume coefficient is obtained on the basis of measured data from representative trees.

Average increment volume (Mirković D., 1993):

for02

v1 - average volume for 2016

v2 - average volume for 2014

n - observation period (3 years, n=3).

 

Results

The presented data and results refer to the monitoring period from 2014 to 2016, during the vegetation period from April to October.

 

Granulometric Composition

The pedological profile P 1, is open on the rythic vertisol, according to the texture composition it is sandy clay along the entire profile (Table 2).

The pedological profile P 2, is open on the rythic vertisol, according to the texture composition it is loam along the entire profile, and in a layer of 1.6 - 1.8 m clayey loam (Table 3).

 

tab02

 

tab03

 

Hydrological Observations and Analyses

In order to give the most realistic presentation of the impact of the HPPIG backwater on "Mlaca" profile, comparative representations of the Danube water level and the duration of flooding in the vegetation and non-vegetation period were presented.

In 2014, at the beginning of the vegetation period (April), compared to the annual average water level for the 1973-2016 period, is characterized by extremely dry conditions in relation to the perennial average. The beginning of the vegetation period in 2015 was within the average level, but in 2016 it was below average. During the summer months of 2016, the levels were above the annual average, while in 2014 and 2015 they were below the average. The end of the vegetation period is characterized by levels that are within the average for 2015 and 2016, while in 2014 levels are well above the average (September, October).

In Figure 8, Flood duration data in the vegetation period are shown as averages for the 1973-2016 period and individually for the analyzed period from 2014 to 2016.

 

fig07
Figure 7: Comparison of annual average Danube water levels for the 1973-2016 period, and Danube water levels for the analyzed periods of 2014, 2015 and 2016.

 

fig08
Figure 8: Level duration curves for the vegetation period (April to October) for the "Mlaca" profile.

 

In accordance with the level duration curve for the average level between 1973-2016, it has been defined that the boundary elevations on the "Mlaca" profile are as follows:

  • 71,30 mnm - level duration for poplar wood 55 days (which meets the conditions for poplar tree survival)
  • 71,01 mnm - level duration for willow wood 85 days (which meets the conditions for willow tree survival)

Values below these established boundaries negatively influence the growth of these forests. Accordingly, it can be concluded that the hydrological conditions for the 2014-2016 monitoring period had deteriorated in comparison to the perennial average.

 

Duration of Floods During the Vegetation and Non-Vegetation Period in the "Mlaca" Profile

During the research period, flood duration data in the "Mlaca" profile were systematically registered and recorded.

 

fig09
Figure 9: Observed flood duration in the "Mlaca" profile in 2014, 2015 and 2016.

 

Figure 9 shows the duration of the flood in the "Mlaca" profile per month. Red indicates the period when the profile was not flooded, while blue indicates the period during which the profile was flooded.

The hydrological situation in 2014 was similar in both profiles. From the end of April until mid-June, as well as the first half of August and September, the profiles were under water. During 2015, the hydrological situation on both profiles was significantly different compared to 2014. In the first quarter of the year, the profiles were influenced by flood waters, and from the second half of June, both profiles were outside the influence of the flood waters. The hydrological situation in 2016 on both profiles was similar, during February and March the profiles were under the influence of flood waters. After that, three short flooding periods were recorded, in mid-May, in June and in November.

 

Dynamics of Capillary Moisture in the Soil


fig10
Figure 10: Dynamics of capillary moisture in the soil for "Mlaca" profiles P 1 and P 2, for 2014, 2015 and 2016, during the vegetation period from April to October.


During 2014 the observed profiles were flooded for most of the vegetation period and the moisture content in the soil had increased. Conditions of maximum saturation without soil aeration resulted in negative conditions for the development of vegetation.

For 2015, it can be concluded that the second half of the vegetation period is characterized by insufficient humidity conditions, while the beginning of the vegetation period is characterized by optimum to insufficient moisture conditions.

During 2016, the moisture content in the soil was similar in the both profiles. At the beginning of the vegetation period the moisture content in the soil was insufficient, and the middle of the vegetation period was characterized by an increased moisture content in the soil. The end of the vegetation period is characterized by insufficient moisture content in the soil.

 

Tree Diameter Increment

The first profile area is about 270 m from the Tamis river bank at an altitude of 71.17 m, and the second profile area is about 130 m from the Tamis river bank at an altitude of 71.36 m.

 

tab04

 

Figure 11 and 12 represent average diameter growth curves for profiles P1 and P2.

 

fig11
Figure 11: Average diameter growth curves for profile P 1.

 

fig12
Figure 12: Average diameter growth curves for profile P 2.

 

Figure 13 and 14 represent average increment volume curves for profiles P1 and P2.

 

fig13
Figure 13: Average increment volume curve for profile P 1.

 

fig14
Figure 14: Average increment volume curve for profile P 2.

 

In the observed period size of increment volume increase are very low, which could be attributed to deteriorated habitat conditions, primarily hydrological conditions. It is certain that high levels of Danube backwater in the spring and first summer days, when the vegetation is most intensive, exert a negative impact on biomass production. Also, long periods of flooding on these profiles effects soil conditions, which adversely affect the root system, reduce aeration, and cause other negative effects on the soil.

 

Conclusion

Habitats for growth and development of forest species on the investigated profiles are quite different. This difference is mainly influenced by an unequal height position, i.e. elevation, which in this case, and given the Danube backwater level and the level of groundwater, has a strong impact.

Groundwater, together with surface waters, has a decisive influence on the soil moistening regime. Influence of Groundwater is conditioned by stratigraphic composition of hydrogeological and soil profiles, their filtration characteristics and capillary capacity. In this sense, the presence of sandy layers and the presence of layers of clayey composition are of great importance. The main influence of surface waters is to provide additional moisture in soil by flooding.

Research conducted on the impacts of the ''Iron Gate I" Hydroelectric Power Station (HPPIG) backwater on soil wettnes and growth and development of poplar Populus euramericana I-214 plantations on the "Mlaca" profile, allowed us to define conditions, above all hydrological conditions, which are necessary for the normal development of forests, primarily Populus euramericana I-214 in the flood plain forests - foreland.

In order to determine more precisely, what period of the year and how much the Danube level and groundwater levels, effect the vegetation in these forests, it is necessary to monitor the capillary moisture and increment volume increase in the vegetation period using the most modern instruments and more frequent follow-up. There is also a need for greater multidisciplinary cooperation in these research efforts.

 

References

Gavrilović Zoran, Jurišić Sonja, Puzović Renata, Impact of HEPP "DJERDAP I" Backwater on Foreland Forests and revitalization, Institute for the Development of Water Resources "Jaroslav Černi", First Serbian Forestry Congress - Future with Forests, Belgrade, 2010.

Marek Sádovský, Perspectives for Danube floodplain forests, DANUBEPARKS project – The Danube River Network of Protected Areas - Development and Implementation of Transnational Strategies for the Conservation of the Natural Heritage at the Danube River (SEE/A/064/2.3/X), WP4 Floodplain Management and Habitat Network, 4.2 Guidelines for Riparian Woodland Management and Sustainable Forestry.

Mirković D., Banković S. (1993). Dendrometrija (in Serbian), Univerzitet u Beogradu, Šumarski fakultet (in Serbian)

Program 6. - Osmatranje, merenje i analiza uticaja uspora Dunava na priobalje izazvanih eksploatacijom HE Đerdap 1, u 2014. godini - osmatranje, merenje i analiza uticaja uspora Dunava na šume u forlandima - izveštaj za 2014. godinu (in Serbian)

Program 6. - Osmatranje, merenje i analiza uticaja uspora Dunava na priobalje izazvanih eksploatacijom HE Đerdap 1, u 2015. godini - osmatranje, merenje i analiza uticaja uspora Dunava na šume u forlandima - izveštaj za 2015. godinu (in Serbian)

Program 6. - Osmatranje, merenje i analiza uticaja uspora Dunava na priobalje izazvanih eksploatacijom HE Đerdap 1, u 2016. godini - osmatranje, merenje i analiza uticaja uspora Dunava na šume u forlandima - izveštaj za 2016. godinu (in Serbian)

Tanja Arizanovic-Eminovic, Dragisa Stevic, Snezana Radonjic-Dmitrovic, Practicum for analysis of physical and chemical soil properties, Institute for the Development of Water resources "Jaroslav Cerni", Belgrade, 2009.