1. Impact of tree species foliage on aquatic macroinvertebrate communities. Andrew Nevin Department of Biological Sciences, York College of Pennsylvania Introduction Aquatic macroinvertebrates play an essential role in breaking down and utilizing nutrients from riparian leaf litter that enter into the streams each autumn. The fallen leaves often form natural “packs” when subjected to flow barriers such as large rocks or branches. These leaf packs provide both food and habitat for a wide variety of aquatic macroinvertebrates. Some of these organisms are primary consumers and represent a crucial link in the aquatic food web between riparian vegetation and higher trophic levels (Gregory et. al. 1991). These ecosystems are highly complex and are regulated by many factors. Some factors such as pollution, substrate composition, and riparian vegetation are all known to influence the structure and integrity of macroinvertebrate communities. Much research has been conducted in order to describe the importance of riparian vegetation in regulating abiotic stream conditions such as water temperature and stream bank erosion. However, less is known about how differences in tree species composition affect macroinvertebrate communities, specifically changes brought on by the introduction of exotic tree species. Such research is necessary to assess the impact of these conditions on natural stream communities. I conducted an artificial leaf pack experiment in two local streams in order to determine if the exotic tree species Ailanthus (Ailanthus altissima) and Norway maple (Acer platanoides) negatively affected macroinvertebrate communities when compared to native leaf litter such as boxelder (Acer negundo) and red maple (Acer rubrum). Research has shown that macroinvertebrate abundance and taxa richness are both negatively correlated with a faster decomposition rate (Bailey et. al. 2001). Since ailanthus foliage has been shown to decompose faster in aquatic systems than most native tree species, I expected macroinvertebrate diversity to be the lowest within these leaf packs (Swan and Healey 2005). Because Norway maple foliage drops after native species, I also expected lower diversity within this treatment since most macroinvertebrates would have already colonized native packs. Methods Leaves were collected from trees during the early autumn months after senescence had occurred. Four grams of leaf material were placed into each LaMotte® Leaf Pack Bag and anchored to the stream substrate. Two Stream Sites: Mill Creek and South Branch Codorus Creek Tributary (Nixon Park). * Five micro-sites for each stream. Four different foliar treatments at each site: Ailanthus, boxelder, red maple, and Norway maple. Two time intervals for retrieval for each foliar treatment: 3 weeks and 9 weeks. Norway maple leaf pack samplers were introduced to the streams at a later date to mimic the natural leaf fall of this species. Upon retrieval, macroinvertebrates were separated from the leaf material and preserved in 70% ethanol for later identification. Leaf mass was also weighed after separation to determine amount of material lost for each sample. Results  The only significant difference in macroinvertebrate community diversity between differential foliar treatments was in the Norway maple treatment after nine weeks at Nixon (see Figure 1).  The higher mean diversity in the Norway maple treatment, however, was not evident at Mill Creek. This may be a result of a lower sample size at Mill Creek due to the loss of three leaf packs in high water.  Diversity (H’) appeared to be weighted both by family richness and family evenness within the Nixon 9 week Norway maple treatment (Figures 2 and 3).  Although ailanthus treatments exhibited the lowest diversity, richness, and abundance at both sites and time intervals, the trend is not statistically significant.  Trends in macroinvertebrate assemblage structure appeared to be correlated with foliar decomposition rate (Figure 4). Discussion Ailanthus foliage supported macroinvertebrate diversity to a higher degree than was expected, despite its faster decomposition rate. Norway maple leaves also supported higher diversity than expected despite its late entry into the streams. * These findings suggest no significantly negative impact of these two exotics on macroinvertebrate diversity. * However, a larger sample size may be needed for more statistical power in analyzing these trends. Acknowledgements Acknowledgements Dr. Karl Kleiner, Research Mentor Francis Valazquez, Environmental Coordinator, Nixon Park Works Cited 1. Bailey, J.K., Schweitzer, J.A., Whitman, T.G. 2001. Salt cedar negatively affects biodiversity of aquatic macroinvertebrates. Wetlands. Vol. 21, No. 3: 443-447. 2. Gregory, S.V., Swanson, F.J., McKee, W.A., and Cummins, K.W. 1991. An ecosystem perspective of riparian zones: focus on links between land and water: Bioscience. 41 540/551. 3. Swan, C. and Healey, B. 2005. The role of native tree species on leaf breakdown dynamics of the invasive tree of heaven (Ailanthus altissima) in an urban stream. EOS Trans. AGU, 86(18), Jt. Assem. Suppl., Abstract: NB22F-03. Data Analysis  Macroinvertebrate community structure was expressed using the Shannon Diversity Index (H’).  H’ is a function of both family richness and evenness.  Family Richness = # of families.  Family Evenness = distribution of individuals among families.  Differential foliar treatment means were compared for each site and each time interval separately through one-way ANOVAs and Tukey’s post tests. Nixon Mill Creek AilanthusBoxelderR. mapleN. mapleAilanthusBoxelderR. mapleN. Maple Family 1. Chironomidae42.043.632.555.29.29.812.035.2 2. Nematomorpha2.62.81.0 1.41.01.42.6 3. Annelida0001.200019.8 4. Hydropsychidae2.81.25.51.20.40 0 5. Perlodidae3.64.09.35.600.600 6. Heptageniidae0.20.40000.200 7. Philopotamidae0.601.000.2 00 8. Elmidae00.600.2000 9. Planariidae00.61.300000 10. Tipulidae0.20.80.30.60000.2 11. Leptophlebiidae0.20000000 12. Baetidae0.20000000 13. Amphipoda00000001.2 14. Gerridae000.300000 15. Taeneopterygidae00000000 16. Isonychiidae00000000 17. Psephenidae0.200.800.4 0.20 Nixon Mill Creek AilanthusBoxelderR. mapleN. mapleAilanthusBoxelderR. mapleN. Maple Family 1. Chironomidae54.660.651.840.831.841.549.012.0 2. Nematomorpha1.21.41.00.33.23.01.60 3. Annelida00.209.82.021.312.614.0 4. Hydropsychidae2.21.63.01.50.20.30.40 5. Perlodidae0.43.01.61.80000 6. Heptageniidae0.21.21.01.50000 7. Philopotamidae00.600.800.30.40 8. Elmidae00.40.2000.300 9. Planariidae00000000 10. Tipulidae00.40.800000 11. Leptophlebiidae00.4000000 12. Baetidae00000000 13. Amphipoda00000000 14. Gerridae00000000 15. Taeneopterygidae00000000 16. Isonychiidae0000.50000 17. Psephenidae00000000 Table 1: Mean aquatic macroinvertebrate abundance per leaf pack by family after three weeks at two stream sites (n=5). Table 2: Mean aquatic macroinvertebrate abundance per leaf pack by family after nine weeks at two stream sites (n=5 except for Mill Creek Norway maple where n=2). Figure 1. Mean (± 95%CI) diversity of macroinvertebrate communities that colonized submerged leaf packs at both Nixon Park and Mill Creek after nine weeks. Means with different letters are significantly different (p<0.05, n=5 except for Mill Creek Norway maple where n=2). Figure 2. Mean (± 95%CI) family richness of macroinvertebrate communities that colonized submerged leaf packs at Nixon Park after nine weeks. Means with different letters are significantly different (p< 0.05, n=5). Figure 3. Mean (± 95%CI) family evenness of macroinvertebrate communities that colonized submerged leaf packs at Nixon Park after nine weeks. Means with different letters are significantly different (p<0.05, n=5). Figure 4. Mean (± SEM) leaf mass remaining after nine weeks in Nixon stream. All leaf packs were introduced with four grams of initial leaf material. Mean Norway maple leaf mass remaining is significantly higher than ailanthus (p<0.05, n=5).