Seventeen high mountain lakes in northern New Mexico were sampled to determine their present biological and chemical condition. In addition, sediment cores were collected at each of the lakes to determine trace metal concentrations, diatom assemblages, and mineralogies as a function of depth. Two of the cores were age-dated using Pb-210 chronology. Eight of the lakes exhibited low alkalinities and, therefore, low capacities for neutralization. These lakes were located in basins where the surface geology was cominated by Precambrian rocks. Atmospheric deposition appears to be contributing acid and trace metals associated with anthropogenic sources to some of the lakes. Trace metal accumulations in the upper layers of Santa Fe Lake began about 60 years ago and about 10 years ago in Truchas Lake. An acid pulse (pH 5.7) associated with snow melt was documented in Santa Fe Lake and correspond with an observed decrease of Daphnia sp. populations. Pea clam densities also appeared to be lower in the low alkalinity lakes. Sediment diatom assemblages in cores from Santa Fe Lake and Truchas Lake appear to be shifting to more acid tolerant species than in the past.

U.S. Geological Survey Grant Number 14-08-0001-G1505