The influence of forest fire on water quality of São Domingos stream (Western Region of Portugal)

Abstract

Forest fires are responsible for several environmental problems, especially for polluting watercourses. In this dissertation we intend to evaluate the changes occurring in the physical and chemical constitution of water of São Domingos stream (crossing the municipalities of Lourinhã and Peniche, Portugal), in particular pH and nutrient content variation, related to surface runoff from the burnt area of the Cezaredas plateau, where a forest fire occurred at July 19^th, 2012. Thus, water samples were collected in three points strategically chosen along this stream (one upstream of the burnt area and two downstream, one of the last being located immediately after the burnt area) from which the pH, the electrical conductivity and the concentrations of N, P, K, Na, Ca and Mg were assessed.

The data obtained in the analysis of the samples collected downstream of the burnt area show an input of nutrients in the stream water and an evidence that nutrient transportation occurs in a higher degree during the first episodes of rainfall which are also responsible for generating surface runoff. This is due to the greater availability of nutrients in these areas and the reduced soil protection, a factor that facilitates surface runoff.

The concentration of nutrients in the water collected from the São Domingos stream, after it had passed through the burnt area, was not very high. This is due to the fact that the burnt area corresponds only to a small proportion of the drained basin in study and, therefore, a dilution effect of the dragged nutrients might have probably taken place.

The analysis of the sampled waters showed a high concentration of Ca, even in those samples collected upstream of the burnt area. These results are explained by the higher availability of this natural element in the study area. On the other hand, the concentrations of P and N were very low in the waters sampled, confirming a migration of small quantities of these nutrients from the burnt areas into the water of the stream, which can be explained by the diminished availability of these elements in these areas.

The results presented in this dissertation demonstrate that the watercourses downstream of the burned areas are more vulnerable to contamination. However, the concentrations of the chemicals evaluated were very small and there is no danger to human health if these waters are consumed.

KEYWORDS: Water; Surface Water Contamination; Surface Runoff; Forest Fire; Nutrient Loss.

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Reference: 

Meneses, B.M. (2013) - Influência de um fogo florestal na qualidade da água da Ribeira de São Domingos localizada na Região Oeste de Portugal. Dissertação de Mestrado apresentada ao Instituto Superior de Agronomia, Universidade de Lisboa.