Trophic Conditions and Water Chemistry of Lakes on Cape Cod, Massachusetts, USA

Abstract

ABSTRACT Sixty lakes and ponds distributed throughout the Cape Cod peninsula were each sampled three times during 1996–1998 in order to determine the chemical conditions of the waterbodies. The study lakes, situated on either glacial moraine, glacial outwash plain or post-glacial sand accumulations, ranged in surface area from 3.6 ha to 301 ha and in maximum depth from 1 m to 26 m. The dominant ionic species in all lakes were Na+ and Cl−, likely due to inputs from sea spray. Conductivity and the relative charge contribution from Na+, Cl− and Mg2+ increased with distance out onto the peninsula, whereas the contribution due to Ca2+ decreased along the same distance gradient. Concentrations of Mg2+ were greater than those of Ca2+ in the study lakes, and the concentrations of the latter cation were very low compared to other areas in the northeast U.S. Except for the eutrophic lakes situated on the post-glacial sand accumulations on the outer tip of Cape Cod, the water bodies were, in general, low in total phosphorus, total nitrogen and chlorophyll-a levels, had high Secchi disk depths, and were best classified as oligotrophic. The pH and alkalinity (except for lakes situated on the post-glacial sand accumulations) declined with distance out onto the peninsula. The mean pH and alkalinity of water bodies located closest to the mainland were 6.8 and 71 μeq·L−1, respectively, but declined to only 5.3 and-7.5 μeq·L−1 on the outer Cape. Findings are compared to other studies in the northeast U.S.