Elsevier

Science of The Total Environment

Volume 408, Issue 24, 15 November 2010, Pages 6172-6178
Science of The Total Environment

Response of soil microbial communities to fire and fire-fighting chemicals

https://doi.org/10.1016/j.scitotenv.2010.09.011Get rights and content

Abstract

Worldwide, fire-fighting chemicals are rapidly gaining acceptance as an effective and efficient tool in wildfires control and in prescribed burns for habitat management. However, despite its widespread use as water additives to control and/or slow the spread of fire, information concerning the impact of these compounds on soil ecosystems is scarce. In the present work we examine, under field conditions, the response of the microbial communities to three different fire-chemicals at normal doses of application. The study was performed with a Humic Cambisol over granite under heath, located in the temperate humid zone (Galicia, NW Spain) with the following treatments: unburned soil (US) and burned soil added with water alone (BS) or mixed with the foaming agent Auxquímica RFC-88 at 1% (BS + Fo), Firesorb at 1.5% (BS + Fi) and FR Cross ammonium polyphosphate at 20% (BS + Ap). The microbial mass (microbial C), activity (β-glucosidase, urease) and community structure [phospholipids fatty acids (PLFA) pattern] were measured on soil samples collected at different sampling times during a 5 year period after a prescribed fire. The results showed a negative short-term effect of the fire on the microbial properties. The microbial biomass and activity levels tended to recover with time; however, changes in the microbial community structure (PLFA pattern) were still detected 5 years after the prescribed fire. Compared to the burned soil added with water, the ammonium polyphosphate and the Firesorb treatments were the fire-fighting chemicals that showed a higher influence on the microbial communities over the whole study period. Our data indicated the usefulness of the PLFAs analysis to detect the long-term impact of both fire and fire-fighting chemicals on the soil microbial communities and hence on the soil quality of forest ecosystems.

Introduction

Wildfires are the major disturbance in forest ecosystems mainly due to vegetation destruction and soil degradation, causing very serious ecological, economical and social problems around the world, particularly in Mediterranean landscapes of European countries (Moreno et al., 1998, Ekinci and Kavdir, 2005, Carballas et al., 2009). The growing concern about this topic has stimulated numerous studies showing that fires induce important changes in physical, chemical and biochemical properties, the impact being determined by fire regimen factors (intensity, duration and recurrence) as well as by local conditions such as vegetation composition, topography or regional climate (Raison, 1979, Chandler et al., 1983, Carballas et al., 1994, Debano et al., 1998, Neary et al., 1999, Johnson and Curtis, 2001, González-Pérez et al., 2004, Certini, 2005, Carballas et al., 2009, Mataix-Solera et al., 2009). In the future, warmer and drier conditions associated with Global Change are expected to increase the area affected by fire (Flannigan et al., 2000); consequently the improvement of wildfire fighting techniques is a global concern.

A variety of chemicals have been increasing its use worldwide to assist in the strategic containment of fires. By definition a fire-fighting chemical is an agent that, either alone or mixed with water, delays or even stops the combustion of a given fuel (Adams and Simmons, 1999). These substances, classified as short-term retardants (those that do not reduce the combustion after evaporation of the water from the fuel) and long-term retardants (those that form a long-term combustion barrier after evaporation of the water), are generally composed of fertilizer salts with a thickening agent or a mixture of surfactants, foams stabilisers and wetting agents or a mixture of surfactants, foams stabilisers, wetting agents and solvents. Most research on these compounds have been traditionally focussed on the evaluation of their effectiveness in aiding fire-fighting and relatively little information is available on the potential environmental effects, including impacts on soils (Giménez et al., 2004). These fire-fighting chemicals are used extensively in natural areas with high environmental value, and available data suggest that there is a significant potential for damage to terrestrial vegetation and to aquatic ecosystems from some of these compounds (Adams and Simmons, 1999, Little and Calfee, 2002, Luna et al., 2007). There is a need to quantify the impact of fire-fighting chemicals on native vegetation and verify their effects on soil properties.

Soil microorganisms are the main agents responsible for long-term sustainability of soil ecosystems since they control the breakdown of organic matter and, hence, the net fluxes and amounts of soil carbon and nutrients through decomposition, mineralization, and immobilization processes (Nannipieri et al., 2003). Changes in several aspects of soil microorganisms (number, mass, activity and diversity) caused by natural or human activities may disrupt the functioning of the soil–plant system and lead to soil degradation; thus, microbial parameters can be used as bioindicators of soil quality changes induced by different soil disturbances (Pankhurst et al., 1997). More than 2000 t of fire retardants are used each year to combat fires in the Mediterranean zones (Luna et al., 2007); there is, therefore, a concern about the effect of fire-fighting chemicals on soil microbial communities in order to preserve soil health. Microbial community-based measurements can be potentially useful for detecting changes in soil quality due to the application of fire-fighting chemicals and therefore to evaluate the environmental compatibility of these compounds. However, despite the common use of fire retardants, surprisingly there is no information on their effects on the microbial soil community. Recent studies performed in the temperate humid zone (NW Iberian Peninsula) have shown that under laboratory conditions microorganisms of both unheated and heated soil samples can potentially be affected at short-term by a fire retardant difficult to biodegrade such as an acrylic-based polymer (Basanta et al., 2002, Basanta et al., 2003, Díaz-Raviña et al., 2006). The data indicated that the fire-fighting chemical at field doses reduced significantly N mineralization and slightly modified microbial biomass and soil enzymatic activities; likewise, microbial community structure, determined by means of the phospholipids fatty acid analyses (PLFA pattern), was affected by the fire-fighting chemical addition. It should be noticed, however, that the microbial changes induced by the fire retardant were less marked than those provoked by the soil heating at 350 °C.

The main hypothesis underlying the present work is that the fire-fighting chemicals at field doses can induce long-term changes in soil microbial communities and hence in soil functioning and quality, in which case they should be used with caution. Therefore, the aim of this study was to examine, under field conditions, the short-, medium- and long-term impact of three fire-fighting chemicals, representative of the compounds often used to combat fires in Mediterranean countries (foaming agent RFC-88 from Auxquímica; terpolymer Firesorb from Stockhausen; and ammonium polyphosphate FR from Cross), at normal application doses on the microbial communities (mass, activity and community structure) of forest ecosystems of the NW Iberian Peninsula.

Section snippets

Experimental design

Soil samples were taken from an experimental field, with UTM coordinates 29 T 05182–46509, located at Alto da Pedrada (Tomiño, Galicia, NW Spain) at an altitude of 455 m a.s.l. The soil, developed over a parent material of paragneises and with a slope of 18–19%, has a vegetation cover dominated by Ulex, Chamaespartium and Erica 50–60 cm height and showed sandy texture, acidic pH and relatively high organic matter (SOM) and C/N ratio values. After a prescribed fire (with the fire extinguished but

Results and discussion

The evolution of the soil enzyme activities in the 0–2 cm layer of all soil treatments along 60 months after the prescribed fire is shown in Fig. 1. The results clearly indicate that the prescribed fire caused an initial decrease in the two soil enzymes studied since values in the burnt soils were 35–46% (urease) and 73–86% (glucosidase) of those in the unburnt soil. This agreed with previous results obtained in other Galician forest soils both heated under laboratory conditions and affected by a

Conclusion

Considering the results overall, we can state the importance of the prescribed fires as a perturbation agent in the dynamics of the forest ecosystems located in the Atlantic humid temperate zone (Galicia, NW Spain), particularly in several aspects of the soil microbial communities such as mass, activity and microbial structure composition. The microbial parameters measured showed a different sensitivity to detect the fire and fire-fighting chemical impacts. Short- and medium-term effects of the

Acknowledgements

This study was supported by the Consellería de Educación y Ordenación Universitaria de la Xunta de Galicia (08MRU002400PR) and by the Ministerio de Ciencia e Innovación (AGL2008-02823), Spain.

References (40)

  • D.G. Neary et al.

    Fire effects on belowground sustainability: a review and synthesis

    Forest Ecol Manag

    (1999)
  • F. Ponder et al.

    Microbial properties and litter and soil nutrients after two prescribed fires in developing savannas in an upland Missouri Ozark Forest

    Forest Ecol Manag

    (2009)
  • A. Saá et al.

    Changes in P fraction distribution and phosphomonoesterasa activity immediately following forest fires

    Soil Biol Biochem

    (1993)
  • E.D. Vance et al.

    An extraction method for measuring soil microbial biomass C

    Soil Biol Biochem

    (1987)
  • R. Adams et al.

    Ecological effects of fire fighting foams and retardants: a summary

    Aust Forestry

    (1999)
  • D. Badía et al.

    Effect of simulated fire on organic matter and selected microbiological properties of two contrasting soils

    Arid Land Res Manag

    (2003)
  • M.R. Basanta et al.

    Microbial biomass and metabolic activity in a forest soil treated with an acrylamide copolímero

    Agrochimica

    (2003)
  • M.R. Basanta et al.

    Biochemical properties of forest soils as affected by a fire retardant

    Biol Fertil Soils

    (2002)
  • M.R. Basanta et al.

    Field data of microbiol response to a fire retardant

    Agrochimica

    (2004)
  • M. Carballas et al.

    Organic matter, nitrogen, phosphorus and microbial population evolution in forest humiferous acid soils after wildfires

  • Cited by (42)

    • Short-term effects of post-fire soil mulching with wheat straw and wood chips on the enzymatic activities in a Mediterranean pine forest

      2023, Science of the Total Environment
      Citation Excerpt :

      The enzymatic activities in the unburned soils measured six months after mulching were generally greater compared to the burned sites, and this is expected (Lucas-Borja et al., 2021). The latter authors stated that the lower enzymatic activity in burned soils is a clear effect of wildfire, which, due to the high soil temperature, destroys a large amount of the enzymes (Barreiro et al., 2010). Moreover, again Lucas-Borja et al. (2021) attributed these differences to the nutrient cycling, climate regulation, waste decomposition, wood production, and water regulation functions, which were lower in the soils subject to wildfire.

    View all citing articles on Scopus
    View full text