Lakebed Pockmarks in Burlington Bay, Lake Champlain II. Habitat Characteristics and Biological Patterns

Abstract

Pockmarks are common features on the bottom of Lake Champlain, especially in the central part of the lake, between Burlington, Vermont and Plattsburgh, New York. Pockmarks have the potential to provide a unique bottom environment for biota because of the different water quality and habitat conditions that may exist inside and outside the pockmark. In Burlington Bay, the “General” is a large pockmark, roughly 40 meters in diameter and 4 meters in depth, located in about 28 meters of water. We collected benthic invertebrate samples inside and outside the “General” pockmark, and collected sediment, pore and overlying water for analysis. We also caged zebra mussels inside and outside the pockmark to determine whether varying water quality or food availability in the pockmark would influence these mussels.

The concentrations of Al, Fe, Ca, K, Mg, Mn, S, Si, and Zn in the overlying water were higher inside the pockmark than outside, with generally highest concentrations near the outside rim of the pockmark rather than at its deepest point. The benthic invertebrate density also varied among sites, with generally more invertebrates inside than outside the pockmark. Clinkers, the remains of coal combustion, were common in the sediment both inside and outside the pockmark. Although clinker density was highly variable, in general, fewer invertebrates were found where the density of clinkers was high. The zebra mussels inside the lip of the pockmark grew less, but had higher shell weight to body weight ratios than those outside the pockmark. This suggests that food might be limited by the water flow pattern in the pockmark, but these mussels were able to take advantage of additional calcium in that water. Mean calcium concentration outside was 14.23mg/L, while inside it was 15.14 mg/L. It also suggests that zebra mussels in the broader lake may be calcium limited.