EFFECT OF FIRE ON WATER AND MAJOR NUTRIENT BUDGETS IN FOREST ECOSYSTEMS : II. NUTRIENT BALANCES, INPUT (PRECIPITATION) AND OUTPUT (DISCHARGE)

Abstract

Concentration and mass of nutrients, pH and temperature in rain and stream water were measured every ten days throughout a year (December of 1979-November of 1980) at three watersheds : strongly burnt, moderately burnt and natural forests in Etajima Island, where a fire occurred in June of 1978 and burnt 1005 ha of forest, in Hiroshima Prefecture, west Japan. Annual range of temperature in the stream water was wider in the burnt forests than in the natural forest, and pH value of the stream water in the strongly burnt forest was always recorded lowest and nearest to that of the rain water in all sites. This finding indicates the problem of reduced buffer action of pH in the watershed-ecosystem after the fire. The concentration of nutrients in the stream was increased (K, Mg and Ca) or decreased (Na) with the increase of flow rate of discharge at all the watersheds. The relation between flow rate of nutrients (qV) and discharge (Q) was approximated closely by an equation : qV=a.Q^b+1. There was little difference in the value of coefficient b among the same nutriests whether the forest was burnt or not, while the value of coefficient α increased in proportion to the intensity of damage to forest by the fire. This suggests that coefficient α is a good indicator of degradation in a watershed-ecosystem. All nutrient balances, which were calculated as the difference between input (precipitation) and output (discharge), changed to minus at the three watersheds, but net loss of nutrients (except calcium)