Original scientific paper
The Impact of Technical and Biological Measures on Soil and Erosion Dynamics in the Research Site of Abrami
Nikola Pernar
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za uzgajanje i ekologiju šuma, Svetošimunska 25 p. p. 422, 10002 Zagreb, HRVATSKA
Danko Holjević
; Građevinski fakultet Sveučilišta u Zagrebu, Fra Andrije Kačića Miošića 26, 10000 Zagreb, HRVATSKA
Darko Bakšić
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za uzgajanje i ekologiju šuma, Svetošimunska 25 p. p. 422, 10002 Zagreb, HRVATSKA
Josip Petraš
; Građevinski fakultet Sveučilišta u Zagrebu, Fra Andrije Kačića Miošića 26, 10000 Zagreb, HRVATSKA
Ivan Perković
; Šumarski fakultet Sveučilišta u Zagrebu, Zavod za uzgajanje i ekologiju šuma, Svetošimunska 25 p. p. 422, 10002 Zagreb, HRVATSKA
Abstract
Soil erosion is one of the most devastating soil degradation processes. In temperate climate regions, soil erosion rarely assumes excessive proportions. In the management of forest soil, the potential erosion threat drastically increases with an increase in climate aridity. Water erosion is particularly favored by parent materials of low water permeability and by soils derived from such materials. In theMediterranean and sub-Mediterranean area of Croatia, these are primarily flysch, marl and Werfen schists. These materials show good physical weathering properties, thus providing a rich source of erosion material.As a rule, the soil formed from such parentmaterial is of silty-clayey to clayey texture, and has a relatively low infiltration capacity. The soil unprotected by vegetation (burned sites) manifests particularly devastating forms of water-induced erosion. In the past 50 years, flysch terrains of Istria have been subjected to a series of technical, biological and biological- technical treatments aimed at preventing water erosion and recovering the eroded soils. An experimental (research) site was set up in Abrami near Buzet for the purpose of monitoring erosion processes and rehabilitation effects of different biological-technical and biological methods of eroded area recovery. The effects of the treatments on soil properties in the research site are in the form of progressive pedogenetic processes. Asynergy of the effects of recovery methods and different natural conditions (relief, vegetation) in the experimental site is particularly well reflected in erosion indicators, such as the production of erosion sediment (erosion production), and to a lesser extent, the surface flow index. For this reason, research in this work focuses primarily on soil properties and erosion production dynamics. From the geological-lithological aspect, the research site of Abrami is made up of Eocene flysch composed of alternate layers of light grey marl and dark lime sandstone, i.e. thinner or thicker interbeds of sandy limestone. The climate is sub-Mediterranean. The mean annual temperature is 12 °C and the mean annual precipitation is 975 mm. The natural potential vegetation in the localities is represented by the community of hop hornbeam and autumn moor grass. Established in 1956 on the slope exposed to highly pronounced erosion processes, the research site has an area of 23.46 ha.Aseries of technical and biological erosion recovery measures had been undertaken in the site by 1963 for the purpose of investigating their applicability in practice. Technical activities included the construction of step-like terraces, of the bench terrace type (»gradoni«), and contour rustic walls. Avariety of plant material was planted and seeds of different plant species were sown in the area (Table 1). Several control plots were also established in parts of the Abrami site, where either no treatment was applied or the seedlings were planted into the planting holes. Six plots intended for the measurement of erosion sediment production were established in 1969, followed by research into the quantitative erosion indicators, which started in 1970 (Table 1). After an interruption in 1977, measurements were resumed in 1997 and 1998 (two plots) and in 1999 (three plots). Erosion indicators have continuously been measured since 2000; however, measurements in plot I (plot I was omitted from this research due to its specific features) have been performed by means of terrestrial photogrammetry. The seventh plot was established in 2004, and has been the subject of measurements since 2005. This work encompasses measurement data from 2005, 2006 and 2007. The research includes plots II, III, IV,V, aswell asVI and VII. The soil and organic residues were sampled in the immediate surroundings of the erosion-measuring plots. Next to the plots in which no technical recovery measures were undertaken, a pedological profile was opened and the soil was sampled by horizons. Some smaller plots of 50 x 50 cm were used to sample the forest floor in 3 points next to the plots (near the top, in the middle of the slope and near the bottom). Undisturbed soil from the depth of 0-5 cm was cylinder-sampled in these smaller plots. The soil profiles next to the terraced plots were not sampled. The forest floor was sampled in small 50 x 50 cm plots, particularly those established on the slopes and on the top of the bench terraces. After the removal of the forest floor, the soil in the small plots was sampled with a probe (disturbed soil) to a 10 cmdepth, and with a cylinder (undisturbed soil) to a 5 cmdepth. The granulometric soil composition was determined according to HRN ISO 11277:2004, the pH according to HRN ISO 10390:2005, the CaCO3 content according to HRN ISO 10693:2004, organic carbon (TOC) according to HRN ISO 10694:2004, porosity according to HR ISO 11508 and 11272 2004, water retention capacity according to HRN ISO 11461:2001, air capacity according to HRN ISO 11580 and 11272:2004, and soil water permeability according to HRN ISO 17312:2005. Measurements of erosion parameters were based on the cumulative measurement of runoff and erosion sediment for each particular rain event (in some cases several rain events were measured cumulatively). Water with eroded particles was determined in the field by measuring water levels in retention basins and/or tubs. The total quantity of erosion sediment in the collected waterwas determined according to theHRNISO 4365 standard. Rain events were registered in the site itself with a pluviograph within the meteorological station of Abrami. In converting the erosion production mass into volume, the average erosion sediment density was assumed to be 1.2 Mg m-3. Statistical analyses (descriptive statistics, correlations, t-test) were performed with STATISTICA 7.1 software. Research into soil physiography in the site did not show any significant differences between the samples, regardless of sampling depths (the pHinwater suspension is between 7.7 and 7.9),which indicates long-term erosion impacts, that is, the homogeneity of the material. The soil in plot II does not have a developed humus-accumulative horizon. It is a strongly skeletal eutric regosol with a discontinued layer of the forest floor (the layer contains 1,531 kg ha–1 of dry organic matter). The soil in the surface 0.5 cmismoderately porous (48.4%), with moderatewater capacity (37%) and low water permeability (Table 2). In plots II and III (one immediately next to the other) the soil is eutric cambisol, with a depth of č90 cm. The depth of the humus-accumulative horizon is only 2 – 4 cm,which reflects the erosion impact in the past. The slightly-to-moderately porous soil has relatively low water permeability (Table 2). In plot V the soil is eroded eutric cambisol with a discontinued A-horizon. This is shallower and texturally lighter soil than the soil in plots III andVII. In terms of granulometric composition, the soil is silty loam.Water permeability is very fast in the surface 5 cm. In plots IV and VI, the soil in the surface 10 cm is of silty-clayey texture, both on the slopes and the terraces. On the terraces of these plots the soil ismore compacted and the forest floor accumulation is higher, but water permeability is lower than on the slopes of the bench terraces. The annual precipitation amount ranged from 908 mm in 2005, over 979 mm in 2006, to 1.167 mm in 2007. During 2005, the least precipitation occurred in the first annual quarter (<100 mm), while in the other 3 quarters the amount of precipitation was very similar. During 2006 and 2007, precipitation amounts by quarters were almost identical: most rainfall occurred in the 1st, followed by the 3rd quarter, and the least occurred in the 4th quarter (Fig. 5). Measurements of surface runoff and erosion production show that the most severe erosion occurred in plot II (Fig. 5). In the early 1970s, the annual erosion production in this plot amounted to over 500 m3 km-2, while during the three-year measurement period it came to between 47.9 and 65.3 m3 km-2.More than half of the erosion production took place in the 3rd annual quarter. Of other plots, distinct production is manifested by plot V and plot VII (Fig. 5 and 6). In the three remaining plots, the annual erosion production is considerably lower and does not exceed 0.5 m3 km-2. There is no significant difference in the dynamics of annual production, except that erosion extremes occurred in plot IV in 2007, which coincides with the extremes in plots II and V. The lowest surface runoff coefficient was identified in plot III and the highest in plot II. Themean annual runoff coefficient in plot II ranges between 0.052 and 0.076, and the maximal comes to as much as 0.397. This suggests a very low infiltration capacity of precipitation water. Namely, in this plot the soil is shallow regosol of silty texture (72% of silt) and of very poor water permeability capacity (k=0.04m/day). Erosion production in plots IV andVI is very low (Fig. 5).Overall biomass production in plot VI is lower than in plot IV, while the quantity of forest floor is similar to that in plot II. On the other hand, better developed trees of black pine and a very dense layer of ground vegetation in plot IV are responsible for higher leaf litter quantities: 3,312 kg ha-1 on the slopes of the bench terraces and 4,144 kg ha-1 on the terraces. It was found that erosion production was lower in the plots with higher organic matter content (in the forest floor and the mineral part of the soil). All these point to a series of mutual impacts, which synergistically determine the rate and intensity of erosion in these plots. This is explained by lower erosion sediment production in Plot IV in comparison with plots V and VI, although the terrain in plot IV has a much steeper slope. On the other hand, it is evident that, compared to plot V in which only biological recovery measures were applied, the application of technical recovery measures in plots IV and VI resulted in a much earlier reduction of erosion intensities. According to the results of research, the application of biological-technical recovery measures increases soil permeability and the soil organic matter content in proportion to the steepness of the terrain. The steeper the terrain, the higher the content is. In this climatic region, the most erodible period occurs in the 3rd quarter of the year. Erosion production in the terrain recovered with biological-technical measures is very low, regardless of the distribution and intensity of precipitation; on the other hand, biological recovery itself, without any technical measures, results in much weaker erosion control.
Keywords
erosion; soil erodibility; soil water permeability; erosion production
Hrčak ID:
68069
URI
Publication date:
8.4.2011.
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