RESUMO
Climate change coupled with inappropriate burning practices has increased large-scale wildfires in Brazilian tropical savannahs (Cerrado). Considering that the effects of ash from wildfires on water parameters are scarcely known in tropical savannahs, this study investigated the chemical changes caused by ash in the soft water, commonly used for bioassays. To this end, ash samples were collected immediately following a fire in a Cerrado area (Federal District, Brazil) and put into water (1:10 ash:soft-water m/v) to check physical parameters under laboratory conditions. Major water-extractable elements (K+, SO42-, Ca2+, PO43-, Na+, Mg2+) from ash strongly altered water quality parameters: elevated total dissolved solids and conductivity levels as well as an increase in pH and decrease in dissolved oxygen concentration were reported over the course of the experiment (15 days) compared to control conditions. Our results point out relevant solubilized compounds from ashes which may potentially impact water quality in post-fire scenarios.
Assuntos
Incêndios , Poluentes Químicos da Água , Incêndios Florestais , Laboratórios , Poluentes Químicos da Água/análise , Qualidade da ÁguaRESUMO
Wildfire is very common in Brazilian savannas, and its effects on water, soil and aquatic/soil organisms are poorly understood. In this study, we observed the effects of fire, especially of ashes, on surface soil and subsurface water in a typical Brazilian savanna (Cerrado sensu strictu) for one year. Soil analyses (pH, organic matter content, potential acidity, K, Ca, Mg and P) and subsurface water analyses (NO3-, PO43- Mg2+, Ca2+ and K+) were assessed. We evaluated the ecotoxicological effects of ashes on three different endpoints and species, in fish Danio rerio (embryonic development), aquatic snail Biomphalaria glabrata (reproduction) and a soil species Enchytraeus sp. (reproduction). We found a higher amount of exchangeable cations and organic matter content in short-term fire effects on soil, but the higher availability of nutrients did not affect the soil pH in field plots. The effects of ashes on soil and subsurface water did not persist for one-year post-fire, except for organic matter content in burned areas. No toxic effects were observed on hatching success and incidences of developmental abnormalities in D. rerio embryos. However, ash input had adverse effects on reproduction in snails and enchytraeids. We reported a statistically significant decrease in snail eggs exposed to the 50g.L-1 and 100g.L-1 of ashes after four weeks (p<0.05, Dunnett's test and Tukey test). Enchytraeus sp. reproduction was negatively influenced by the natural soil, which presents high acidity, and also when exposed directly to the ashes from burned area, suggesting that pH and other ash compounds may limit the growth of enchytraeids. More studies in burned areas are strongly encouraged, addressing the potential important routes of exposure to ashes in order to understand the impact of intense fires on soil and aquatic biota in tropical savannas.
Assuntos
Biota , Pradaria , Solo/química , Água/química , Incêndios Florestais , Animais , Brasil , EcotoxicologiaRESUMO
In a global scenario of climate change, several studies have predicted an increase in fires in different parts of the world. With the occurrence of rains following the fires in the Brazilian savanna (Cerrado biome), the compounds present in ashes may enter aquatic environments and cause adverse effects to these ecosystems. In this context, this study evaluated the potential toxicity of ashes from two areas of Cerrado and an area of pasture, through ecotoxicological bioassays and using three aquatic species from distinct trophic levels, which were exposed to different dilutions of ashes: the microcrustacean Ceriodaphnia dubia, the fish Danio rerio and the mollusc Biomphalaria glabrata. The ashes from the three sampled areas showed higher concentrations of some elements in relation to the soil samples (B, Ca, K, Mg, Mn, P, S, Si, Sr, Zn), but only a small quantity of these compounds was solubilised. Our data showed that all ash samples caused acute toxicity to C. dubia (48hs-LC50 = 13.4 g L-1; 48hs-LC50 = 6.33 g L-1; 48hs-LC50 = 9.73 g L-1 respectively for transition area, pasture, typical cerrado areas), while in relation to D. rerio and B. glabrata, no acute toxicity was observed when they were exposed to ashes from native Cerrado vegetation and pasture areas. Ashes from a transition area showed toxicity for D. rerio (48hs-LC50 = 25.0 g L-1); possibly, this was due to the combination of multiple preponderant inorganic elements of ashes with other organic compounds not analysed, such as polycyclic aromatic hydrocarbons (PAHs). In summary, these results suggest that wildfires may pose risks to zooplankton communities and emphasize the need for more studies to better understand the complexity of the ecological effects of fire on aquatic ecosystems.