The Impact of Forest Fire on the Nutrient Influxes to Small Lakes in Northeastern Minnesota

Abstract

The Little Sioux fire of May 1971 burned most of the mixed coniferous—deciduous forest on the watersheds of Meander and Lamb lakes, two small, low conductivity lakes located in the Boundary Waters Canoe Area (BWCA) of northeastern Minnesota, USA. During 1972, hydrologic and chemical (Ca, Mg, K, Na, and P) budgets were determined for the terrestrial watersheds of Meander and Lamb lakes and for the lakes themselves. Budgets were also measured for Dogfish Lake, a lake physically and chemically similar to Meander Lake but whose watershed was not burned in the Little Sioux fire. These budgets show that the atmosphere supplies a significant fraction of the cations and phosphorus (Ca, 90%; Mg, 35%; K, 95%; Na, 55%; P, 95%) to the BWCA watersheds, with the remainder coming from chemical weathering. The budgets are similar to those reported for other Canadian Shield lakes and watersheds. The impact of the Little Sioux fire on nutrient fluxes was evaluated by comparing the budgets measured at Dogfish Lake with those measured at Meander Lake. This comparison showed that as a result of the burning of Meander Lake watershed, runoff increased 60% and the K and P exports increased 265% and 93%, respectively. The exports of Ca, Mg, and Na did not change significantly. The increase in runoff, probably due to the reduction in vegetative transpiration, is comparable to that measured after the 1970 Entiat fire (western Washington) and to that resulting form clear—felling experiments at Hubbard Brook (New Hampshire) and Coweeta (North Carolina). The increased nutrient losses after fire are less than those observed at Hubbard Brook and Coweeta. There was no indication of a drastic increase in nitrate export such as occurred after the Entiat fire and at Hubbard Brook. The increase in phosphorus loading of Meander Lake due to the fire was 38% (to 25 mg/m2°yr), a value that probably falls within the natural year—to—year variation in supply, and it did not represent a major impact on Meander Lake. Fire is a natural part of the BWCA forest ecosystems. The results of this study indicate that nutrient losses after the Little Sioux fire were minimal, perhaps because it was a spring fire. Fall fires may cause larger nutrient losses because more of the forest—floor material is likely to be consumed and revegetation does not begin until the following spring.

Sustaining Aquatic Ecosystems in Boreal Regions

“…Both paleoecological studies (Wright and Heinselman 1973, Ritchie and Yarranton 1978, Payette et al 1989 and long-term studies of boreal lakes and streams in remote areas (Schindler et al , 1996a(Schindler et al ,b, 1997 show that boreal terrestrial ecosystems are strongly affected by natural phenomena such as fire, windthrow, and insect outbreaks, which in turn are strongly affected by climate and weather. Lakes and streams are affected by these terrestrial disasters, as well as directly by climate and weather (Wright 1976, Schindler et al 1980, Bayley et al 1992a,b, Schindler 1998.…”

“…Burned catchments have higher streamflows and water and nutrient concentrations for several years following fire, with the greatest changes following the most severe burns (Wright 1976, Bayley et al 1992a). Yields of base cations (Ca, Mg, Na, K) increased after fire, but increases in strong acid anions (SO 4 , NO 3 , Cl) were even greater, causing a net acidifying effect on streams (Bayley et al 1992b).…”

Fire Effects on Soils in Lake States Forests: A Compilation of Published Research to Facilitate Long-Term Investigations

“…However, persistent increases in mineral soil N, P and K have been reported by repeated measurements over ten years following experimental burning in immature jack pine in the Lake States region [57]. Fire-caused increases in soil nutrients (such as inorganic N forms) may increase nutrient losses due to leaching, although studies of wildfire effects in mixed-conifer forest in the Boundary Waters Canoe Area showed that these effects also decreased with time since fire and were not large enough to cause lake eutrophication [77,80]. However, our calculations of overall mean effect size showed that fire increases soil P (total and extractable) and cations (Ca, K and Mg) and decreases soil total, inorganic, organic, and soluble N forms.…”

Synthèse des impacts écologiques des feux et des coupes forestières sur les lacs de l'écozone boréale au Québec

“…(2000), les concentrations de COD dans les « lacs de coupe » excèdent l'étendue de variation naturelle observée dans les lacs de référence lorsque le rapport de drainage est > 4 et que les coupes ont déboisé plus de 30 % de la surface du bassin versant. Une hausse de phosphore et d'azote après des feux ou des coupes de forêt (LIKENS et al, 1970 ;NICOLSON, 1975 ;BAYLEY ef al., 1992 ;MINSHALL ef al., 1997) et de COD après des coupes (PLAMONDON ef al., 1982) a souvent été rapportée dans les cours d'eau mais plus rarement dans les lacs (WRIGHT, 1976 ;RASK ef al., 1993RASK ef al., et 1998. Une reconstruction paléolimnologique des concentrations de PT, NT et COD faite dans un lac humique de l'écozone boréale de l'Abitibi (Québec) ayant subi 4 feux importants depuis 2 000 ans BP, a aussi indiqué une augmentation moyenne de 50 % des concentrations de PT après les feux mais pas changement dans les concentrations de COD (ENACHE et PRAIRIE, 2000).…”

“…Au cours des deux dernières décennies, les réponses des écosystèmes lacustres aux perturbations par l'acidification, l'eutrophisation, l'augmentation de la radiation UV et les changements du climat ont été bien étudiées (SCHINDLER, 1998). En revanche, très peu de recherche a porté attention aux effets des feux et des coupes forestières sur les écosys-tèmes lacustres (WRIGHT, 1976 ;RASKef a/., 1993RASKef a/., , 1998. Récemment, une première étude comparative à grande échelle des impacts des feux et des coupes sur la qualité des eaux et les communautés aquatiques des lacs de l'écozone boréale de l'est du Canada a été réalisée de 1996 à 1998 dans le cadre d'un projet du Réseau de centre d'excellence sur la gestion durable des forêts (RCE-GDF) (CARIGNAN et STEEDMAN, 2000).…”