USING ACIDITY DIFFERENCES IN NORTHERN NEW YORK RIVERS TO EXAMINE POROSITY CHANGES IN FRESHWATER CLAM SHELLS

The major rivers in St. Lawrence County, northern NY flow north and empty into the St. Lawrence River. Along their path, they flow through the Adirondack highlands and the Adirondack lowlands, regions that are mainly distinguished by their topography and the difference in the exposed bedrock. Due to the weak buffering capacity of metaigneous rocks in the southern highlands compared to the metasedimentary and sedimentary rocks of the northern lowlands, we can observe a decline in water pH towards the south. Using this cline in acidity, we are examining the impact pH has on the shell formation of the freshwater bivalve Elliptio complanata that lives in these waters.

Sixteen localities and more than 600 individuals were samples including highland samples (southern Raquette R.) and lowland samples (northern Raquette R., Oswegatchie R.). Volume and shell density parameters were measured using the buoyant weight techniques, using a density determination kit. The dry mass of the shell, saturated mass of the shell, and buoyant mass of shells were recorded. A Mann-Whitey test was used to test for significant differences between river samples.

Microdensity is similar amongst the comparison groups with southern Raquette R. being the lowest (2.68 g/cm³) followed by the northern Raquette R. (2.69 g/cm³) and the Oswegatchie R. (2.71 g/cm³). Porosity percentages show that the southern Raquette R. shells have an average porosity of 10.9%, the Oswegatchie R. 7.48 %, and northern Raquette R. 7.35%. Comparing these samples indicates that there is a significant difference between the porosity of the shells from the northern and southern Raquette R. (p=2.751e-18). Further analysis shows that the samples from the Oswegatchie R. differ significantly from the southern Raquette shells (p=9.386e-19), but are not significantly different from the northern Raquette R. (p=0.6735).

Our data shows that clam populations that live in the lowlands river sections grow shells that are less porous than specimens that live in the highlands. Since overall streambed morphologies and anthropogenic activity are comparable between the river sections, our data indicate that the pH of the water plays an important role in shell formation, causing the formation of more porous shells in more acidic environments and less porous shells in more alkaline habitats.