Impact of Native Tree Species Foliage on Aquatic Invertebrate Communities

Branden Birth

Department of Biological Sciences, York College of Pennsylvania

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Table 1. Mean aquatic macroinvertebrate abundance per leaf pack by family at Richard Nixon Park (n=10 per species of foliage)

Family B. Walnut R. Oak R. Maple Tulip Poplar

1. Philopotamidae 1.0 0.3 2.0 0.7 2. Tipulidae 0.3 0.4 0.9 0.1 3. Heptageniidae (Epeorus sp.)* 0 0 0.1 0 4. Heptageniidae (Stenonema sp.)* 0 0.1 0.2 0 5. Chironomidae 23.5 64.3 28.8 42.9 6. Oligochaeta 0.3 1.2 0.4 0.5 7. Hydropsychidae (Cheumatopsyche sp.)*

1.2 2.6 0.8 0.5

8. Elmidae 0 0.1 0.2 0.1 9. Isonychiidae (Isonychia sp.)* 0 0.1 0.1 0 10. Planariidae 0 0.6 0 0.7 11. Hydrachnida 0.1 0 0 0 12. Psephenidae (Psephenus sp.)* 0 0.1 0 0

* Family and Genus were identified

Introduction

• Aquatic macroinvertebrates are very important for nutrient cycling and organic decomposition in aquatic ecosystems surrounded by riparian vegetation zones (Malmqvist 2002). Macroinvertebrates colonize fallen foliage from the riparian zones for food and shelter and help support necessary aquatic food webs.

• Research shows that the species composition of the riparian vegetation zones surrounding aquatic ecosystems play a significant role in the species composition, species richness, and abundance of inhabiting aquatic macroinvertebrates (Yanoviak 1999). Some research has been completed investigating the effects of native versus exotic tree species foliage on aquatic macroinvertebrate communities (Nevin 2005), but baseline data on the impact of native foliage species on these macroinvertebrate communities is lacking.

• Artificial leaf packs are widely used in experiments investigating relationships between tree foliage and benthic macroinvertebrates. The packs (leaves in mesh bags) allow a mass of previously collected foliage to be easily contained and attached to a stream or river substrate while also allowing natural colonization of the leaf pack by macroinvertebrates.

• During the fall of 2007, I investigated the effects of native tree species litter on macroinvertebrate diversity, family evenness, and family richness at Nixon Park in York County, PA. Studies that investigate the effects of current forest composition on macroinvertebrate diversity will provide an important baseline for future studies on changes in riparian forest stand composition.

Question Asked

1. How do differing native tree species foliage impact the diversity of colonizing aquatic macroinvertebrates?

Methods

• Leaves were collected from 4 native species after they had fallen from their respective species of tree in the beginning of October

• Some collected leaves were used to create a linear regression of dry leaf mass versus wet leaf mass

• Leaf material was placed in mesh leaf pack bags and attached to stream substrate with metal stakes

• 10 sites were chosen within the stream at Richard Nixon Park

• Each site contained 4 different foliar groups (40 total, N=10 per species): Black Walnut, Tulip Poplar, Red Maple, and Red Oak

• Samples were retrieved after 7 weeks and refrigerated in plastic jars

• Macroinvertebrates were counted and removed from leaf material and stored in 70% ethanol for later identification

• Remaining leaf material was dried and massed

Statistical Analysis Macroinvertebrate colonization of leaf pack was calculated using the Shannon Diversity Index (H’)

(H’) is influenced by family richness and family evenness

Family Richness is the total number of families

Family Evenness is the distribution of individuals among families

Foliage group means were compared at each site using one-way ANOVA and Tukey’s post tests

Results No significant difference in microinvertebrate community diversity was found when comparing foliage groups means at each site (Figure 1).

Diversity (H’) appeared to be influenced more by family evenness than family richness (Figure 2 and 3).

No significant difference was found in the total number of individuals when comparing foliage groups (Figure 4).

A significant difference was found when comparing the remaining dry leaf mass of foliage groups (Figure 5).

Figure 1. Mean (± 95% CI) diversity of macroinvertebrate communities that colonized leaf packs

after seven weeks. Means with different letters are significantly different (p<0.05,n=10 per species).

Figure 2. Mean (± 95% CI) family evenness of macroinvertebrate communities that colonized leaf packs after seven weeks. Means with different letters are significantly different (p<0.05, n=10 per species).

Figure 3. Mean (± 95% CI) family richness of macroinvertebrate communities that colonized leaf packs after seven weeks. Means with different letters are significantly different (p<0.05, n=10 per species).

Conclusions All four foliage groups equally supported macroinvertebrate diversity even though decomposition rates of foliage groups were not equal.

A slower decomposition rate of Red Oak and Red Maple foliage may suggest a chemical composition that deters against physical decomposition by macroinvertebrates

A slower decomposition rate of Red Oak and Red Maple may be a result of macroinvertebrates using these foliage species for shelter rather than a food source.

Works Cited

1. Malmqvist, B. 2002. Aquatic invertebrates in riverine landscapes. Freshwater Biology. 47:679-694.

2. Nevin, A. 2005. Impact of exotic tree species foliage on aquatic macroinvertebrate diversity in two Pennsylvania streams. Sr. Thesis Manuscript: York College of PA Biology Department.

3. Yanoviak, S.P. 1999. Effects of leaf litter species on macroinvertebrate community properties and mosquito yield in Neotropical tree hole microcosms. Oecologia. 120:147-155. Acknowledgements

Dr. Kleiner, Research Mentor

Nixon Park Staff

Figure 4. Mean (95% CI) total number of individuals for each foliage group. Means with different letters are significantly different (p<0.05,n=10 per species).

Figure 5. Mean (95% CI) mass of remaining dry leaf matter for each foliage group. Means with different letters are significantly different (p<0.05,n=10 per species).

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