Forms of Phosphorus in Sediments Eroded from Burnt Soils
1994
Saá, A. | Trasar-Cepeda, M. C. | Soto, B. | Gil-Sotres, F. | Díaz-Fierros, F.
Wildland fires can increase erosion and nutrient loss in runoff by loss of vegetative cover and changes in soil structure and chemical composition. Thus, we investigated the effect of vegetation burning intensity on the loss of particulate P forms in eroded sediments by using a sequential fractionation method that distinguishes organic and inorganic P forms of different lability. Moderate burns, while not affecting P form distribution in the soil, led to high levels of inorganic P (largely Bic-Pi, NaOH-Pi, and HCl-P) in eroded sediments, with phosphorus enrichment ratios ranging from 3.36 to 5.04. Severe burns modified P form distribution in the soil, and led to the almost complete disappearance of extractable organic P from the soil. Phosphorus form distribution in sediments eroded from the severely burnt plot was similar to that in the surface layer of the soil of that plot (0–2.5 cm). Within 10 mo of burning, and independently of burn intensity, sediments eroded from both the moderately and severely burnt plots had the same P form content and distribution as sediments eroded from control plots. As a consequence of burning, the annual total P losses due to removal of particulate matter in runoff increased from 1.42 kg ha⁻¹ (control plot) to 4.35 kg ha⁻¹ (moderately burnt plot) and 9.10 kg ha⁻¹ (severely burnt plot). The results of the P fractionation reveal that burning leads to a 2- to 11-fold increase in rapid-turnover inorganic and organic P contents in eroded sediments. This implies greatly increased risks of eutrophication of receiving waters.
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