Characteristics of Lake Sediments of the South Bay, Andover Lake, CT. abstract by Brian McCan
Andover Lake in Tolland County, CT experienced algal blooms in 1996 and 1997, thereby dimishing the quality and temporarily reducing the recreational utility of the lake. Algal blooms are attributed to overproductivity of lacustine biota primarily due to elevated levels of phosphorous, a limiting nutrient that is introduced to lakes from both natural and anthropogenic sources. Phosphorous precipitates out from the water column and accumulates in lake-bottom sediments at concentrations far greater than in the water. As a result, it is important to determine concentrations and availability of phosphorous and other elements within lake sediments.

The quality of water in Andover Lake has been monitored since 1996, while studies analyzing lake-bottom sediments have been conducted since 2000. The research has found that water quality for the lake has improved since 1996, although elevated concentrations of phosphorous occur in lake-bottom sediments. However, in general iron is present at sufficient concentrations in lake sediments to inhibit the reintroduction of phosphorous to the water column under well-oxygenated conditions.

The present study examines sediments in the south bay of Andover Lake, a site where future dredging may become necessary. Sediment cores were collected at three sites along a transect that extends out of the bay. These cores reveal varying thicknesses of sediments that have accumulated since the lake was damned in 1927. The shallow “bay” core contains 38cm, the middle “old road” core 110cm, and the deltaic core 147cm of post-damming lake sediment. These differences in thickness are due to pre-lake conditions, and the proximity to the outflowing Erdoni Creek. Physical (moisture content, organic carbon and inorganic carbon content) and chemical (Aq, B, Be, Bi, Ga, Hq, La, Mo, Na, Sb, Sc, Tl, U, and W) analysis from the cores indicates the presence of three sedimentary units, including a lowermost pre-lake unit, a transitional unit deposited rapidly soon after damming, and an uppermost lake sediment unit. Concentrations of phosphorous and other elements are highest in modern lacustrine sediments (Unit III), but diminish dramatically at depths greater than 60cm in unit I and II. Iron concentrations are high enough to prevent phosphorous from entering the water column under oxic conditions. These findings suggest that future dredging will mix the most chemically concentrated sediment first, but due to the high iron concentrations, they will not likely introduce significant quantities of phosphorous to the lake.