This study investigated the relationship between historical fires and sediment carbon accumulation in lakes over the past three centuries in northern Wisconsin. Fires may increase nutrient availability as terrestrial vegetation is eliminated, increasing primary production in adjacent water bodies and carbon accumulation in lake sediments. However these effects could be short-lived if vegetation recovers quickly following fire. Alternatively, fires may reduce the productivity of adjacent lakes by reducing the availability of allochthonous carbon inputs in the form of terrestrial particulate organic carbon, an important subsidy to oligotrophic seepage lakes of northern Wisconsin. In an effort to better understand the relationship between historical fires on the landscape and carbon accumulation in lakes, sediment cores from three different lakes in the Northern Highlands Lake District were collected and analyzed for charcoal and carbon. Cores were extruded into half-centimeter intervals and subsamples were dated using 210Pb. Charcoal pieces in sub-samples were identified, counted and then analyzed with the program CHARSTER. Carbon content was determined by coulometry.
Results/Conclusions
Lakes in close proximity to one another showed differences in their sediment records of fire and carbon accumulation. The differences suggest that historical fires may have had local, watershed-specific effects and that sedimentation characteristics of a lake may influence its record of fire. Trends in sediment carbon accumulation also differed across lakes. One seepage lake showed higher carbon values in sediments over a period of greater fire frequency relative to an era of fire suppression while the other seepage lake showed increasing carbon and charcoal accumulation in more recent decades, in spite of fire suppression. Sediment carbon content in the drainage lake appears to be more closely coupled with fire events, declining during periods of fire and increasing following fire suppression. These differences could suggest differences in the supply of allochthonous carbon to lakes with different hydrological regimes. Drainage lakes may integrate more carbon originating from the leaf litter and forest floor, a supply that may be interrupted during fire events. Seepage lakes may integrate carbon originating higher in the canopy that may be relatively unaffected by low intensity fire events. Differences in the sediment records of the three lakes suggest strong landscape heterogeneity.
