FROM THE DEPTHS OF GREAT POND: ANTHROPOGENIC AND NATURAL INFLUENCES ON BOTTOM SEDIMENTS AND THE IMPLICATIONS FOR LOCAL SUSTAINABILITY

Current research consists of collecting bottom sediment samples from Great Pond. Samples were analyzed to create a sediment map of the lake basin in regards to depth, grain-size distribution, organic content (%C), C:N ratios and phosphorus concentration. Great Pond has the largest surface area (3,453 ha) of the 7 lakes in the watershed. It receives most of its water from East and North Ponds via Great Meadow Stream, as well as the surrounding uplands and groundwater. Lake volume was increased by the construction of a hydroelectric dam in 1886.

To evaluate natural and anthropogenic changes in the lake environment, 67 samples were collected using an Ekman dredge. Multiple sedimentologic and geochemical proxies will be used to infer in-lake ecological responses. Grain-size will be used to determine sediment source. Grain-size analysis of the samples indicates a predominance of silt and clay-sized sediment related to the underlying glacio-marine Presumpscot Formation. Other samples, however, contain sand and pebble-sized sediments indicating a local esker and outwash sources. Total organic carbon (TOC) was used to evaluate biomass productivity, while C:N ratios was used to determine the source of organic matter in the sediment. C:N ratios from the samples range between 8 and 11, indicating a nonvascular plant (algal) origin for the organic matter in the sediment. These results will be compared with previous research on nearby East Pond sediments. The resulting sediment map will be used to determine sediment sources and areas of higher erosion. Sediments will also be analyzed for phosphorus content to determine anthropogenic impact on the system.

This research will add to the geologic knowledge base of lake sedimentation and chemistry which can be used by local conservation groups for community education and advocacy for best sustainability practices. Results will aid in the understanding of the glacial formation of the lake, distribution of sediment within, and human impact on the lake. Additionally, knowing the distribution of phosphorus within the sediments may allow development of a strategy to avoid accelerated eutrophication. The resulting map of sediment distribution and Google Earth placemarks will be housed on an appropriate website for viewing and study by stakeholders and the scientific community.