GEOCHEMICAL AND MICROFOSSIL RECORD OF MASS HEMLOCK DIE-OFFS IN THE SEDIMENT OF BARTON'S COVE, WESTERN MASSACHUSETTS

In recent years, the Hemlock Woolly Adelgid (HWA), has aggressively infested the North American hemlock (Tsuga canadiensis) leading to massive die-offs that have changed woodland ecosystems. One effect has been the loading of local watersheds with dissolved organic matter and nutrients leading to eutrophication of lakes and ponds. The northeastern U.S. has seen such hemlock declines before, in a succession of events ranging from~6000 - 4800 years before present. Most studies have suggested these die offs occurred due to a series of draughts evidenced in the pollen and tree ring records. The effects of Hemlock declines are being accentuated by the rebound of earthworm populations in New England, decimated after the Wisconsin glaciation. The worms are cycling dissolved organic carbon (DOC), nitrogen and phosphorus out of soil organic matter much faster than they can be recycled into the forest biota, such that large amounts of these nutrients are flushed into nearby bodies of water, causing further eutrophication.

To examine the history of nutrient runoff, an 8-meter core was recovered from Barton’s Cove, a former plunge pool that lies 117 kilometers north of the mouth of the Connecticut River. The low-energy environment of the pool makes it an ideal sink for fine-grained sediments and the organic material that runs off from the surrounding forest. Radiocarbon dates indicate that the core contains sediments spanning the last 6194 years BP. This range includes the other major Holocene hemlock declines and massive die-offs. Organic matter content is high in these sections of the core, ranging from 40% to ~75% TOC, and the carbon isotopic values of the organic matter indicates a mainly terrestrial origin (-33.5‰ to -28‰). We will attempt to quantify the changes in nutrient loading to Barton’s Cove during the hemlock die-off by both direct measurement of total phosphorous and by Diatom analysis. The findings of this project may contribute to predicting ongoing changes due to hemlock declines and rapid soil organic mobilization by the Woolly Adelgid and earthworms, respectively.