Seasonal variation in leaf-litter breakdown in nine boreal streams: implications for assessing functional integrity

Abstract

Although leaf-litter breakdown rates have been suggested as a complementary bioassessment tool to measure stream functional integrity, surprisingly few studies have assessed how seasonal variability in decomposition might affect detection of impact. In this study, leaf-litter breakdown (Alnus glutinosa (L) Gaertner) was assessed during two seasons (spring and autumn) and over three years to determine the efficacy of this method for detecting human-induced change. The leaf-litter breakdown studies, performed in nine boreal streams in south-central Sweden along a gradient of nutrient enrichment, gave little support to the conjecture that rates of decomposition were related to nutrient enrichment. Only fine mesh bags in one season (autumn-winter 2005) showed a significant effect of impact. Seasonal differences in leaf mass loss in coarse mesh bags after 34 and 55 days of incubation and in fine mesh bags after 34 days were attributed to changes in temperature. In addition, other factors such as high water levels resulted in the loss of many litter bags confounding data interpretation.