Decomposition during autumn foliage leaf-fall in wetlands situated along a biogeochemical gradient in Pennsylvania, USA

Abstract

Autumn leaf fall represents an important allochthonous organic input to inland, aquatic ecosystems, particularly those situated in mixed hardwood forests. We evaluated factors that influence leaf decomposition in wetlands situated along a strong biogeochemical gradient spanning the ridge and valley region in the mid-Atlantic region in the United States. Leaf decomposition rates were estimated using mesh bags; at the same time, algal and invertebrate colonization on the leaf packs was measured. Leaf decomposition exhibited an exponential decline over the 35-day incubation period; rates were similar to those of previous studies (range 0.15–0.40 per day) and not significantly different (one-way ANOVA, F = 0.67, p = 0.526). Mean chlorophyll-a (mg/m2) on leaf packs increased among sampling dates and generally was 10-fold greater in the transition and valley wetlands (22.88 and 29.20 mg/m2) compared with the ridge (2.24 mg/m2) wetland (F = 14.78, p < 0.001). Invertebrate biomass on the leaf packs exhibited significant spatial variation among wetlands (one-way ANOVA, F = 32.1, df = 2, p = 0.0001). The ridge site supported significantly lower biomass compared with both transition and valley wetland sites. Shredders and collectors were dominant at the ridge site, while scrapers and predators were abundant in the transition and ridge wetlands; this provided strong evidence for the importance of algae as a food source in these benthic communities. Algal biofilm growth on leaves in these sites appears to reflect a unique trophic dynamic that may represent an important sink for recycled nutrients.