FROM THE DEPTHS OF GREAT POND (MAINE): ANTHROPOGENIC AND NATURAL INFLUENCES ON BOTTOM SEDIMENTS AND THE IMPACT ON LOCAL SUSTAINABILITY

As part of a Maine EPSCoR grant focusing on sustainability in the Belgrade Lakes watershed of central Maine, 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 discharge. Lake volume was increased by the construction of a hydroelectric dam in 1886. Results from this investigation will aid in the understanding of the glacial formation of the lake, distribution of sediment within, and human impacts. Additionally, knowing the distribution of phosphorus within the sediments may allow development of a strategy to avoid accelerated eutrophication.

To evaluate natural and anthropogenic changes in the lake environment, 67 bottom sediment 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 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 phosphorous content to determine anthropogenic impact on the system.

This research will add to the geologic knowledge base of lake sedimentation and chemistry and will provide data that can be used by local conservation groups for community education and advocacy for best sustainability practices for lake management.