Calculations:Sedimentation rates were calculated by:

Post-damming sediment depth * pond area / years since pond establishment

0.31m * 5900m2 / 30yr 60m3 * yr-1

Results and DiscussionThe first 11cm of the core were hydric, unconsolidated peat and muck; below this layer were 17cm of more solid peat and muck. At 28cm depth, there was a 3cm deep layer of banded, gray, mineral sediment with little organic matter, which we believe was deposited immediately after the drainage was dammed. Thereafter, wetland vegetation contributed to the accumulation of the organic sediments present in the top 28cm of the core. At the core bottom was an organic, woody-debris rich soil, which suggests trees were once present where the pond currently exists, corroborating both our interpretation of the 1942 aerial photograph and the presence of standing dead trees in the pond. These layers are represented to-scale in the image at far left.

AbstractIn this study, we estimate the volume of sediment that has accumulated in a 0.59 hectare beaver pond at the Green Mountain Audubon Center, Huntington, VT, during the past 30+ years of intermittent beaver activity. Interpretation of aerial photographs and correspondence with local landowners (LaBarr, pers. comm. 2005) corroborate our age estimates for the pond. Sediment cores from the bottom of the pond reveal discrete layers of unconsolidated peat and muck, mineral sediment, and buried forest soil, suggesting fairly abrupt changes in hydrology during periods of beaver activity, resulting in ~ 60m3/year of sediment deposition or 1800m3 total sediment deposited.

The beaver pond at the Green Mountain Audubon Center

Beaver Ponds in the Sherman Hollow Brook Watershed: Sediment Deposition and Happy Rodents

Introduction and MethodsBeavers (Castor canadensis) have long been recognized as agents of ecological change. Their dams create wetlands that are home to diverse assemblages of plants and animals. Like mill ponds, beaver ponds trap mineral and organic sediments that would otherwise be transported by the channel they dam.

To determine sedimentation rate over the past 30 years, we collected a 48 cm core from a point approximately in the center of the beaver pond at the Green Mountain Audubon Center, Huntington, VT. We photographed the core in situ (right) and later sub-sampled the core for analysis of sediment type under a dissecting microscope.

ReferencesLaBarr, Mark. October 21, 2005, personal communication.

Aerial Photograph InterpretationA 1942 aerial photograph (left, A) reveals what is currently a beaver pond/wetland complex to have once been a patchwork of field and mixed forest with no evidence of beaver activity. The 1962 aerial photograph (left, B) shows the beginnings of wetland establishment, but only minimal changes in hydrology. Recent aerial orthophotos (1999, left, C) show an 3.4 hectare beaver meadow/pond complex, including a 0.59 hectare pond. This photograph also shows considerably more tree cover than was present in 1942 and 1962 photographs, which is representative of the overall trend of agricultural abandonment in New England.

Amanda Devine1 & Andrea Pearce2

1Department of Botany University of Vermont, Burlington, Vermont, USA 2Department of Civil & Environmental Engineering University of Vermont, Burlington, Vermont, USA

AcknowledgementsThe authors thank the Green Mountain Audobon Society for granting access to the site. Equipment was generously loaned from the Department of Botany. Support and review of this work was done by fall 2005 GEO151.

A local beaver and its handiwork

Unconsolidated organic peat and muck to a depth of 11cm. Graminoid duff visible throughout.

Somewhat more compressed peat and muck to a depth of 28cm. Organic debris slightly more decomposed than in preceding layer.

Mineral layer at 28cm depth, likely deposited just post damming.

Dark, organic rich soil (possibly buried forest soil) from 30cm to the bottom of the core. Fine woody debris throughout.

48 cm core taken from approximate pond center