Ľubomír Lichner

PLANTS AND BIOLOGICAL SOIL CRUST INFLUENCE THE HYDROPHYSICAL PARAMETERS AND WATER FLOW IN AN AEOLIAN SANDY SOIL

This study tested the hypothesis that the changes in hydrophysical parameters and heterogeneity of water flow in an aeolian sandy soil have the same trend as the process of succession. Three sub-sites were demarcated at the area of about 50 m x 50 m. The first sub-site was located at the pine-forest glade covered with a biological soil crust and represented the initial stage of succession. The second sub-site was located at the grassland and represented more advanced stage of succession. The third sub-site was located at the pine forest with 30-year old Scots pines and represented advanced stage (close to climax) of succession. The sandy soil at the surface was compared to the soil at the pine-forest glade at 50 cm depth, which served as a control because it had a similar texture but limited impact of vegetation or organic matter. It was found that any type of vegetation cover studied had a strong influence on hydrophysical parameters and heterogeneity of water flow in an aeolian sandy soil during hot and dry spells. The changes in some hydrophysical parameters (WDPT, R, k(-2 cm), Sw(-2 cm), ECS and DPF) and heterogeneity of water flow in an aeolian sandy soil had the same trend as the process of succession, but it was not so in the case of Ksand Se(-2 cm), probably due to the higher content of smaller soil particles in grassland soil in comparison with that content at other sub-sites. Both the persistence and index of water repellency of pure sand differed significantly from those of grassland, glade and forest soils. The highest repellency parameter values in forest soil resulted in the lowest value of both the water sorptivity and hydraulic conductivity in this soil in comparison with other soils studied. The highest value of ethanol sorptivity and the lowest value of saturated hydraulic conductivity in the grassland soil in comparison with other soils studied were due to the higher content of fine-grained (silt and clay) particles in the grassland soil. The effective cross section and the degree of preferential flow of pure sand differed significantly from those of grassland, glade and forest soils. The change in soil hydrophysical parameters due to soil water repellency resulted in preferential flow in the grassland, glade and forest soils, while the wetting front in pure sand area exhibited a form typical of that for stable flow. The latter shape of the wetting front can be expected in the studied soils in spring, when soil water repellency is alleviated substantially. The columnar shape of the wetting front, which can be met during heavy rains following long dry and hot spells, was attributed to redistribution of applied water on the surface to a series of micro-catchments, which acted as runon and runoff zones. V príspevku sa testovala hypotéza, že zmeny hydrofyzikálnych parametrov a heterogenita prúdenia vody v piesočnatej pôde majú rovnaký trend ako proces sukcesie. Na ploche asi 50 m x 50 m sa vytýčili tri parcely. Prvá parcela sa nachádzala na čistine pokrytej biologickým pôdnym pokryvom a reprezentovala počiatočné štádium sukcesie. Druhá parcela sa nachádzala na zatrávnenej ploche a reprezentovala rozvinutejšie štádium sukcesie. Tretia parcela sa nachádzala v borovicovom lese a reprezentovala rozvinuté štádium sukcesie (blízke ku klimaxovej vegetácii). Piesočnatá pôda na povrchu parciel sa porovnávala s pôdou z čistiny v hĺbke 50 cm, ktorá slúžila ako kontrola, pretože mala skoro rovnakú textúru, avšak veľmi malý vplyv vegetácie alebo organickej hmoty. Zistili sme, že akýkoľvek typ študovaného vegetačného pokryvu mal veľký vplyv na hydrofyzikálne parametre a heterogenitu prúdenia vody v piesočnatej pôde počas horúcich a suchých období. Zmeny niektorých hydrofyzikálnych parametrov (WDPT, R, k(-2 cm), Sw(-2 cm), ECS a DPF) a heterogenity prúdenia vody v piesočnatej pôde mali rovnaký trend ako proces sukcesie, neplatilo to však v prípade Ksa Se(-2 cm), pravdepodobne v dôsledku vyššieho obsahu malých pôdnych častíc v pôde s trávnatým pokryvom v porovnaní s inými parcelami. Stálosť aj index vodoodpudivosti čistého piesku sa štatisticky významne líšili od hodnôt týchto parametrov v pôde pod trávou, biologickým pôdnym pokryvom a borovicami. Najvyššie hodnoty parametrov vodoodpudivosti v tráve pod borovicami mali za následok najnižšie hodnoty sorptivity pre vodu a hydraulickej vodivosti v tejto pôde v porovnaní s ostatnými študovanými pôdami. Najvyššie hodnoty sorptivity pre etanol a najnižšie hodnoty nasýtenej hydraulickej vodivosti v pôde pod trávou v porovnaní s inými pôdami boli pravdepodobne spôsobené vyšším obsahom malých pôdnych častíc v tejto pôde. Efektívny prierez (ECS) a stupeň preferovaného prúdenia (DPF) čistého piesku sa štatisticky významne líšili od hodnôt týchto parametrov v pôde pod trávou, biologickým pôdnym pokryvom a borovicami. Zmeny hydrofyzikálnych parametrov pôdy v dôsledku jej vodoodpudivosti mala za následok preferované prúdenie v pôde pod trávou, biologickým pôdnym pokryvom a borovicami, zatiaľ čo čelo omáčania v čistom piesku malo tvar typický pre stabilné prúdenie. Takýto tvar čela omáčania možno vo všetkých študovaných pôdach očakávať na jar, keď je vodoodpudivosť pôdy podstatne znížená v dôsledku jej zvýšenej vlhkosti. Čelo omáčania v tvare prstov, ktoré možno očakávať počas prívalových dažďov nasledujúcich po dlhých suchých a horúcich obdobiach, možno pričítať redistribúcii vody na povrchu pôdy do viacerých mikropovodí, ktoré sa správali ako vtokové a odtokové oblasti.

Estimating hydraulic conductivity of a sandy soil under different plant covers using minidisk infiltrometer and a dye tracer experiment.

The objective of this study was to estimate the hydraulic conductivity of sandy soil under different plant cover at the locality Mláky II at Sekule (southwest Slovakia). Two sites were demarcated at the locality, with mainly moss species at glade site, and pine forest at forest site. The estimation of unsaturated hydraulic conductivity was conducted by (a) minidisk infiltrometer and (b) the analysis of a dye tracer total resident concentration. The latter approach assumed the applicability of the stochastic—convective flow theory in the sandy soil. In the dye tracer experiment, two plots (1 × 1 m each) were established in both sites, and 100 mm of dye tracer (Brilliant Blue FCF) solution was applied on the soil surface. Similar results were obtained in both plots, with more than 70 % area of horizons stained in the depth of 30–50 cm. In some cases, the predicted and measured hydraulic conductivity were found within an order of magnitude, thus revealing similar impact of different plant cover on hydraulic properties of sandy soil studied. In contrast to sandy soils used for agriculture, the influence of the plant/surface humus and topsoil interface extended in the form of a highly heterogeneous matrix flow to the depth of 50–60 cm, where it was dampened by horizontal layering.

Pines influence hydrophysical parameters and water flow in a sandy soil

Pines, used for sand dune stabilization, can influence the hydrophysical parameters and water flow in an aeolian sandy soil considerably, mainly due to soil water repellency. Two sites, separated by distance of about 20 m, formed the basis of our study. A control soil (“Pure sand“) with limited impact of vegetation or organic matter was formed at 50 cm depth beneath a forest glade area. This was compared to a “Forest soil” in a 30-year old Scots pine (Pinus sylvestris) forest. Most of the hydrophysical parameters were substantially different between the two soil surfaces. The forest soil was substantially more water repellent and had two-times the degree of preferential flow compared to pure sand. Water and ethanol sorptivities, hydraulic conductivity, and saturated hydraulic conductivity were 1%, 84%, 2% and 26% those of the pure sand, respectively. The change in soil hydrophysical parameters due to soil water repellency resulted in preferential flow in the forest soil, emerging during a simulated heavy rain following a long hot, dry period. The wetting front established in pure sand exhibited a form typical of that for stable flow. Such a shape of the wetting front can be expected in the forest soil in spring, when soil water repellency is alleviated substantially.

The impact of heating on the hydraulic properties of soils sampled under different plant cover.

The impact of heating on the peristence of water repellency, saturated hydraulic conductivity, and water retention characteristics was examined on soils from both forest and meadow sites in southwest Slovakia shortly after a wet spell. The top 5 cm of meadow soils had an initial water drop penetration time WDPT at 20°C of 457 s, whereas WDPT in the pine forest was 315 s for the top 5 cm and 982 s if only the top 1 cm was measured. Heating soils at selected temperatures of 50, 100, 150, 200, 250 and 300°C caused a marked drop in water drop penetration time WDPT from the initial value at 20°C. However, samples collected in different years and following an imposed cycle of wetting and drying showed much different trends, with WDPT sometimes initially increasing with temperature, followed by a drop after 200–300°C. The impact of heating temperature on the saturated hydraulic conductivity of soil was small. It was found for both the drying and wetting branches of soil water retention curves that an increase in soil water repellency resulted in a drop in soil water content at the same matric potential. The persistence of soil water repellency was strongly influenced by both the sampling site and time of sampling, as it was characterized by the results of WDPT tests.

Plant transpiration and net entropy exchange on the Earth’s surface in a Czech watershed

The influence of plant transpiration on the entropy exchange was quantified as associated with the degradation of solar energy on the Earth’s surface covered by plants. Two surfaces were studied: (1) productive surface — plant transpiration taken as equal to the potential one, (2) non-productive surface — plant transpiration taken as equal to zero. The entropy exchanges associated with the absorption of solar radiation and with the conversion of absorbed solar radiation into the sensible heat and latent heat were taken into account. These processes were examined in the experimental watershed Liz (828–1074 m a.s.l.) located in the Bohemian Forest (Czech Republic). We found that in the growing season 1992 the net entropy exchange in humid hydrologic period (the Earth’s surface is productive) was considerably higher than in the arid one (the Earth’s surface was productive in 39% of days, and non-productive in 61% of days). Considering that the biotic effect on the Earth’s functioning can be measured with the help of the net entropy exchange, we can assume that the theory that biotic activities — represented by plant transpiration here — are the cause of the self-organizing processes in Earth’s environment is proved in the watershed scale.

Ponded infiltration into soil with biopores — field experiment and modeling

Preferential movement of water in macropores plays an important role when the process of ponded infiltration in natural porous systems is studied. For example, the detailed knowledge of water flow through macropores is of a major importance when predicting runoff responses to rainfall events. The main objectives of this study are to detect preferential movement of water in Chernozem soil and to employ numerical modeling to describe the variably saturated flow during a field ponded infiltration experiment. The infiltration experiment was performed at the Macov experimental station (Calcari-Haplic Chernozem in Danubian Lowland, Slovakia). The experiment involved single ring ponded infiltration. At the quasi steady state phase of the experiment dye tracer was added to the infiltrating water. Then the soil profile was excavated and the penetration pattern of the applied tracer was recorded. The abundance of biopores as a product of fauna and flora was found. To quantify the preferential flow effects during the infiltration experiment, three-dimensional axisymmetric simulations were carried out by a two-dimensional dual-continuum numerical model. The water flow simulations based on measured hydraulic characteristics without consideration of preferential flow effects failed to describe the infiltration experiment adequately. The 3D axisymmetric simulation based on dual-permeability approach provided relatively realistic space-time distribution of soil water pressure below the infiltration ring.

Ongoing succession of biological soil crusts increases water repellency — a case study on Arenosols in Sekule, Slovakia

After soil surface disturbances biological soil crusts (BSC) cover rapidly the topmost soil millimeters. Depending on BSC age, development of soil water repellency, water infiltration and soil surface stability are influenced by this thin surface sealing. Within this study disturbed, early- mid- and late successional stages of BSC development were examined along a recovery transect. The results show an increase in water repellency and a decrease in water sorptivity and conductivity with ongoing BSC succession. Penetration resistance data shows very stable thin surface protection by cyanobacteria in early successional BSC that is non-repellent. Later successional stages show increased water repellency and lower water conductivity. We conclude that BSC development induces changes in surface structure and wettability. The soil surface wettability is strongly linked to the BSC community composition.

Spatial variability of hydrophysical properties of fallow sandy soils

Abstract Spatial heterogeneity of soil hydrophysical properties was estimated in 2 fallow sandy soils at Csólyospálos and Örbottyán, Hungary. Significant differences in small particle (= silt + clay) content (5.0% vs. 13.7%), organic matter content (1.62% vs. 0.91%), and CaCO3 content (3.1% vs. 5.1%) measured at Csólyospálos and Örbottyán, respectively, resulted in a higher persistence of water repellency in the Csólyospálos soil. It also resulted in a significantly higher water sorptivity and hydraulic conductivity of the Örbottyán soil. The spatial heterogeneity of soil hydrophysical properties was significant reaching 3 orders of magnitude differences due to the variances of soil properties. The water repellency cessation time was inversely related to the hydraulic conductivity and water sorptivity at Csólyospálos site.

A new method for estimating soil water repellency index

Abstract The soil water repellency index, R, is calculated from the ethanol sorptivity, Se, and water sorptivity, Sw, using an equation: R = 1.95 Se/Sw. In the older method, Se and Sw were measured in pairwise arrangements to reduce the influence of spatial heterogeneity of soil properties, and one value of R only was calculated from one pair of Se and Sw measurements. The new method to estimate R takes into account all the measured values of water and ethanol sorptivity, i.e., m × n values of R are to be calculated from m values of Sw and n values of Se. The results of the t-test revealed that there is not a statistically significant difference between the means of both samples at the 95.0% confidence level for all four studied soils. It was found using the F-test that there is not a statistically significant difference between the variances of samples estimated by the older and new methods at the 95.0% confidence level for all but one (grassland soil) studied soils. Comparison of R values taken in sandy soil under different vegetation cover in Sekule, southwest Slovakia, revealed that the average values of R estimated using the new method increased with vegetation succession, i.e., Pure sand < Glade soil < Grassland soil < Pine-forest soil, while the me|an values of R, estimated using the older method changed in the order: Pure sand < Grassland soil < Glade soil < Pine-forest soil. It seems that an increase in the number of R values processed can result in the more reliable mean values of R at the sites with high spatial heterogeneity of soil properties.

Effects of vegetation at different succession stages on soil properties and water flow in sandy soil

Abstract The effects of vegetation at different succession stages on soil properties and water flow were assessed in sandy soil at 3 experimental sites near Sekule village (southwest Slovakia). Site S1 was a pioneer site dominated by mosses, site S2 was an early successional stage with a thin stand of grasses, and site S3 was an early successional stage (more advanced compared to the previous), richer in species, with a denser stand of grasses. It was found that vegetation at different succession stages affected soil properties and water flow in sandy soil, but the order of changes in some soil properties and water penetration depths were different from the order of succession stages.