Miroslav Tesař

Field measurement of soil water repellency and its impact on water flow under different vegetation

Numerous recent laboratory studies have shown that vegetation can influence soil water flow by inducing very low levels of water repellency. In this study we extended on this previous research by developing a field-based test using a miniature infiltrometer to assess low levels of water repellency from physically based measurements of liquid flow in soil. The field-based test was verified through a simple laboratory experiment and then applied to determine the impact of vegetation and antecedent soil water content. The soil hydraulic properties determined were hydraulic conductivity, sorptivity, as well as the persistence and index of water repellency. Tests were conducted following a dry spell and wet spell on (1) forest soil (0 cm depth), (2) glade soil (0 cm depth) and (3) glade soil (50 cm depth). It was found that both the persistence and index of water repellency, R, decreased in the order as follows: forest soil > glade soil (0 cm) > glade soil (50 cm) for both dry and wet spell. The range of values of R was 0.28 (wettable) to 360 (highly water repellent), which affected hydraulic conductivity kr(−2 cm). R increased and hence kr(−2 cm) decreased in the order: forest soil < glade soil (0 cm) < glade soil (50 cm) for both the dry and wet spell. There were clear interactions between vegetation and changes to water flow caused by presence of repellency.

Influence of vegetation cover on thermal regime of mountainous catchments

Air temperature at heights of 5 and 200 cm above soil surface, as well as soil temperature at depths of 15, 30 and 60 cm were studied in the cold climatic zone at three localities (catchments) under different plant cover during the growing season of 2002. The catchments Kout (dead forest), Doupě (clearing) and Stolec (mature spruce forest) are situated in the National Park of the Šumava Mts. (Czech Republic) in elevation of 1105–1330 m a.s.l., in which Kout and Doupě form some small “islands” inside an extensive spruce forest. Plant transpiration was not limited by water shortage in all the three localities. It was found that both soil and air temperatures were influenced with plant cover. In hot and dry days, the extremes in daily and night air temperatures were a function of transpiring vegetation height, with higher daily maximum and lower night minimum for smaller vegetation. For the whole growing season (from 29 July to 10 October 2002), the mean values of air temperature were independent upon the plant cover, but the magnitude of the dispersion variance followed the sequence in ascending order: mature forest-clearing-dead forest.

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.

Rainfall interception and spatial variability of throughfall in spruce stand

Abstract The interception was recognized as an important part of the catchment water balance in temperate climate. The mountainous forest ecosystem at experimental headwater catchment Liz has been subject of long-term monitoring. Unique dataset in terms of time resolution serves to determine canopy storage capacity and free throughfall. Spatial variability of throughfall was studied using one weighing and five tipping bucket rain gauges. The basic characteristics of forest affecting interception process were determined for the Norway spruce stand at the experimental area - the leaf area index was 5.66 - 6.00 m2 m-2, the basal area was 55.7 m2 ha-1, and the crown closure above individual rain gauges was between 19 and 95%. The total interception loss in both growing seasons analyzed was 34.5%. The mean value of the interception capacity determined was about 2 mm. Throughfall exhibited high variability from place to place and it was strongly affected by character of rainfall. On the other hand, spatial pattern of throughfall in average showed low variability.

Root Function: In Situ Studies Through Sap Flow Research

Sap flow measured by the Heat Field Deformation technique, HFD, is sensitive to flow responses to small changes in water potential gradients within the tree hydraulic systems. When these changes occur abruptly, under experimental treatments (severing, localized irrigation, heavy loading), sap flow movement can be used as a marker to study root functionality, for example root ability to redistribute water and withstand heavy machinery pressure. Experiments also showed that a compensation mechanism may operate in trees, with a temporary increase in the absorbed water due to a preferential use of one part of the root system when another part is damaged or when a water source is lost. Long-term measurements of root sap flow allow distinguishing between water uptake from shallow and deep rooted trees, at different exposures at a forest edge and from healthy and infected trees. Root sap flow can be used as an indicator of tree stress or of the prevailing mechanisms used by trees to survive drought, under irrigation or rain-fed conditions.

Forest vegetation affecting the deposition of atmospheric elements to soils

Atmospheric inputs of elements/ions into the soil through bulk precipitation and throughfall (precipitation below tree canopies) were monitored monthly at two forested catchments (Lesni Potok and Liz) in central and southwestern Bohemia, respectively. The annual deposition fluxes (expressed in μg/mg m−2 yr−1) of Al, As, Ba, Be, Ca, Cd, Cl−, F−, Fe, K, Mg, Mn, Ntot, Na, Ni, Pb, Rb, SO42−, Sr and Zn between 1997 and 2005 were calculated from their concentrations in monthly collected samples of both precipitation types. The flux of H+ was calculated from the monthly pH values as well. The more pristine character of the Liz catchment was manifested in lower inputs of anions of strong inorganic acids (mostly of anthropogenic origin) and of H+ in spite of higher precipitation amounts at the site. The comparison of fluxes in bulk precipitation (BP) and throughfall (TH) has shown significantly higher values for Rb, K, Mg, Mn, F−, Ca, SO42−, Sr, Ba and Cl− in the latter flux. It is declared that high fluxes of these elements/ions in TH significantly affect the forest soil water chemistry and that the forest vegetation significantly contributes to the mobilization of several elements in soil and to their redistribution throughout the soil profile.

Role of vegetation in the variability of water regimes in the Šumava Mts forest

Deviations between observed and simulated discharge in the basins along the borders of the Czech Republic with Austria and Germany provide outputs which enable to follow changes in runoff. The three basins range in area from 100 to 200 km2 and the experimental basin Liz with an area of 0.99 km2. The selected experimental catchments are situated in or close to the National Park of the Šumava Mts. This region is described also in Tesař et al. (2006). Results indicate that changes in runoff appear to be related to damages in forest cover caused by wind disasters and insects damages.Daily time series used for simulations are approximately 40 years long and 20 years in the experimental basin. Two different models of the rainfall — runoff process have been used for simulations and the outputs provide comparable results. The models are the conceptual model Sacramento (Burnash, 1995) and the model BROOK’90 (Federer, 1993). The second model distinguishes the details concerning evapotranspiration, including transpiration, rain and snow interception and snow and soil evaporation.The indicated runoff changes seem to be rather complex. After deforestation the volume of runoff generally increases and peak flows of floods are higher, but low flow in rainless periods show complicated courses.

Seasonal snow accumulation in the mid-latitude forested catchment

The study deals with the snow cover characteristics (snow depth — SD and snow water equivalent — SWE) concerning the mid-latitude forested catchment. Namely, the influence of the forest canopy (Picea abies (L.) Karst. and Fagus sylvatica L.) and altitude (ranging from 835 m a.s.l. to 1118 m a.s.l.) was investigated. Forest cover was proved to have a significant influence on the snow cover accumulation, reducing SWE by 50 % on average, compared to open sites. The elevation gradient concerning SWE ranged from 30 to 40 mm and from 5 to 20 mm per 100 m in open and forested sites, respectively. Its magnitude was found to be temporarily variable and positively related to the total seasonal snowfall amount. The SWE/SD variability among measurement sites (with different altitude) was higher in open sites compared to forested ones. The catchment SWE/SD variability increases significantly in the snowmelt period (March–April) both in open and forested locations. The differences among snow interception losses, concerning various elevations and the forest canopy, were not statistically significant.

Influence of vegetation cover on air and soil temperatures in the Šumava Mts. (Czech Republic)

Air temperature at heights of 5 and 200 cm above soil surface, and soil temperature at depths of 15, 30 and 60 cm, were measured in the cold climatic zone at three localities (catchments) under different plant cover during the growing seasons 2002-2007. The catchments Kout (dead forest), Doupě (clearing) and Stolec (mature spruce forest) are situated in the National Park of the Sumava Mts. (Czech Republic) at an elevation of 1105-1330 m a. s. 1. This region is part of the metamorphic complex – Moldanubicum. It is formed mainly by metamorphosed rocks (paragneiss with smaller anomalies). The three catchments have very similar natural conditions, but differ significantly in vegetation cover. The catchments are covered with acid brown soil developed on paragneiss. The clearing and dead forest catchments both exist as small islands inside an extensive spruce forest. The following conclusions were obtained from the interpretation of measured data: (1) The air temperature of the catchment covered by the dead forest had a greater daily fluctuation compared to the stands covered by clearing or mature forest. (2) The air temperature of catchments covered by mature forest had the smallest daily fluctuations. (3) The more extreme air temperatures in the dead forest caused the systematic raising of the soil temperature at a depth of 15 cm compared to soil in the clearing and mature forest. These conclusions are valid for a cold climatic zone during a vegetation season in which plant transpiration plays a governing role in solar energy dissipation.

Recovery from acidification alters concentrations and fluxes of solutes from Czech catchments

Changes in atmospheric deposition, stream water chemistry, and solute fluxes were assessed across 15 small forested catchments. Dramatic changes in atmospheric deposition have occurred over the last three decades, including a 70% reduction in sulphur (S) deposition. These changes in atmospheric inputs have been associated with expected changes in levels of acidity, sulphate and base cations in streams. Soil retention of S appeared to partially explain rates of chemical recovery. In addition to these changes in acid–base chemistry we also observed unexpected changes in nitrogen (N) biogeochemistry and nutrient stoichiometry of stream water, including decreased stream N concentrations. Among all catchments the average flux of dissolved inorganic nitrogen (DIN) was best predicted by average runoff, soil chemistry (forest floor C/N) and levels of acid deposition (both S and N). The rate of change in stream DIN flux, however, was much more closely correlated with reductions in rates of S deposition rather than those of DIN. Unlike DIN fluxes, the average concentrations as well as the rates of decline in streamwater nitrate (NO3) concentration over time were tightly linked to stream dissolved organic carbon/dissolved organic nitrogen ratios DOC/DON and DON/TP rather than catchment characteristics. Declines in phosphorus adsorption with increasing soil pH appear to contribute to the relationship between C, N, and P in our study catchments. Our observations suggest that catchment P availability and its alteration due to environmental changes (e.g. acidification) might have profound effects on N cycling and catchment N retention that have been largely unrecognized.