|Edna B. Sussman Final Report
Support by the Edna Bailey Sussman Foundation was used to complete research on aquatic insect communities in central New York rivers during the summer of 2008. Water chestnut (Trapa natans) is a highly invasive aquatic plant originally from Eurasia. Though cultivated for food in parts of Asia and protected as an endangered species in parts of Europe, its spread into North American waterways has been synchronous with measured negative ecological effects. The plant is capable to outcompeting and displacing all native communities of aquatic plants and, once established in a waterway, it becomes difficult to eradicate. My research focuses on determining if the replacement of a native aquatic plant bed by T. natans is followed by a change in the native aquatic invertebrate community. This research is done as part of an internship with the Central New York Regional Planning and Development Board, under the direction of Mrs. Kathy Bertuch, Environmental Program Manager.
During the early summer of 2008, the Seneca and Oswego Rivers were monitored in known sites of previous water chestnut invasion sites. As the plants attained peak biomass in late July, two sites in each river were chosen as sampling sites. At each of the four sites a bed of water chestnut bed and a bed of native water lily (Family Nymphaeaceae) were chosen. Sampling for macroinvertebrates, namely insects, mulluscs and crustaceans, took place from July 31st to August 13th. The sampling method was derived from previous work done by Dr. David Strayer, who investigated macroinvertebrate communities in T. natans in the Hudson River. Using a self-constructed Downing box, six locations within or alongside each bed were sampled for macroinvertebrates, as well as the corresponding plant material. The invertebrates were sieved through a mesh filter and preserved in ethanol for identification in the laboratory located in Illick Hall on the SUNY-ESF campus. All plant material taken from the Downing box was placed in plastic bags, labeled and kept in a cooler for transport back to the SUNY-ESF campus. Along with the Downing box samples, quadrats of 20 cm by 20 cm were also collected to determine plant biomass levels at each sampling site. These plant materials were also placed in bags within coolers and transported back to the SUNY-ESF campus. Abiotic characteristics of temperature, dissolved oxygen and water depth were also recorded at each Downing box sampling site. Water chestnut is known to drastically lower dissolved oxygen within lake settings and the lowering of dissolved oxygen may have a negative effect on the macroinvertebrate population size that a water chestnut bed can support versus a native bed.
Laboratory work has been ongoing on this research project since August. All plant material was washed to remove any invertebrates and then the plants were identified down to species. The plants were then oven dried to remove all water content to make comparisons between sites and plant species possible. The forty-eight bottles (each one representing a Downing box sample) were then sorted through, with identifications completed through the order level. This first round of data has allowed some interesting patterns to emerge. Another highly invasive organism, the zebra mussel (Dreissena polymorpha) seems to prefer beds of invasive water chestnut to beds of native plants. Quadrat sampling has also shown that unlike beds of water chestnut located in lakes, beds located in rivers are rarely monospecific. Both native and invasive aquatic plant species (i.e. curly pondweed and Eurasian watermilfoil) were commonly found within beds of water chestnut.
These preliminary discoveries have laid the foundation for further work with my samples. In order to look at the configuration of invertebrate communities in these aquatic plant beds at a higher resolution, the samples are going to be re-identified, to at least the family order. Statistical tests will be used to determine if the abiotic factors differ between native beds, invasive beds, and areas of no aquatic vegetation. Statistical testing will also be used to determine if, and by how much, each invertebrate community differs from each other based on plant bed composition, plant bed biomass, river locality, temperature, dissolved oxygen, water depth, and location within or along the bed.
This is the first research that examines the effects of water chestnut on insect communities in inland rivers. The results and conclusions that will be derived from this research will aid in a variety of fields. Any change to the insect community will be felt further up the food chain, and so any future work that entails the conservation of larger organisms will need to take into account the effect that any change in plant community is having on the ecosystem. The current difficulty of eradicating this plant from central New York waterways means that this plant will play a prominent role in the ecological welfare of the watershed ecosystem, and this research can be one of the first experiments to statistically show how much of the aquatic system is being affected by this one plant. The final report on this data will be presented in my completed thesis. My thesis and any future presentations and publications derived from this research will prominently display the generosity of the Edna Bailey Sussman Foundation in supporting this research.