Intensity and Persistence of Soil Water Repellency in Pine Forest Soil in a Temperate Continental Climate under Drought Conditions

Edyta Hewelke,Ewa Górska,Dariusz Gozdowski,Marek Kondras,Lidia Oktaba,Izabella Olejniczak

doi:10.3390/w10091121

Abstract

Although soil water repellency (SWR) has been reported under different soils, climates, and vegetation types of the world, especially in forest land and following wildfires, the understanding of this variable continues to be rather limited. This study presented the characterization of SWR from wild fire measurements in a Scots pine Peucedano-Pinetum forest in the Kampinos National Park (central Poland), which is characterized by a temperate continental climate. The main objectives were: [i] To evaluate the potential occurrence, intensity, and persistence of soil water repellency in the surface layers of podzolized rusty soils during a dry summer; [ii] to determine whether a wildfire increased SWR, compared to the unburnt condition of soil; and [iii] to identify changes in hydrophobicity 13 months after a fire. The Water Drop Penetration Time (WDPT) test was used to assess persistence and intensity of soil SWR. Hydrophobicity is a natural phenomenon during periods of drought in temperate continental climates. The extreme class of SWR was observed in surface layers of up to 20 cm. A higher hydrophobicity was noted in the older habitats of the Peucedano-Pinetum forest. Maximum WDPT values (10,800 s) were found for an older ecosystem cover, during a dry summer. SWR in fire-affected soils is dependent on the intensity of the fire, as well as displaying spatial and seasonal variability. Thirteen months after a fire, the highest variability in the occurrence of non-wettability, was recorded in the surface layers of areas affected by a weak fire. A positive relationship between soil pH and WDPT values was determined to a 20 cm depth. Prolonged dry periods resulting from global climate change, may enhance the effects of increasing SWR; it therefore seems reasonable for future research on biosphere–climate interactions, to take the presence of hydrophobicity into account.

Highlights

Increases in the frequency and intensity of droughts are predicted to greatly affect the carbon and water cycles of the terrestrial biosphere [1], with harsh consequences to the functions and services supplied by forests [2,3,4]
Granged et al [36] concluded that soil water repellency (SWR) was usually higher at the soil surface, where the presence of hydrophobic substances is common after low-intensity burning, and decreased with depth; they did not show significant differences between soils which had not been burnt for a long time, and unburnt soils under pines
With regard to our observations, SWR is a natural phenomenon, which occurs in a temperate continental climate in a Brunic Arenosol forest, during dry summer periods

Summary

Introduction

Increases in the frequency and intensity of droughts are predicted to greatly affect the carbon and water cycles of the terrestrial biosphere [1], with harsh consequences to the functions and services supplied by forests [2,3,4]. In Reference to Goebel et al [6], low soil moisture content, in combination with high temperatures, can increase soil water repellency (SWR). Soil water repellency affects hydrological and ecological soil functions [7]. SWR indirectly affects soil CO2 efflux, by exerting an influence on soil moisture distribution [13,14]

Methods

Discussion

Conclusion