A Limnological Survey of Third Sister Lake, Michigan with Historical Comparisons

Abstract

ABSTRACT Third Sister Lake in southeastern Michigan has been a focus of ecological studies since 1904. In 1999, we surveyed several physical, chemical, and biological parameters of the lake and compiled data collected by University of Michigan students since 1975. Comparison of dissolved oxygen profiles from years 1927–29, 1939–42 to recent data (1992–99) indicate a decrease in maximum oxygenation of bottom waters at fall turnover (8 mg O2·L−1 maximum 1927–29, 1939–42 vs. 4 mg O2·L−1 1980, 1992–93) and more rapid depletion of oxygen in the hypolimnion following stratification. In early studies, oxygen persisted (> 3 mg L−1) at all depths from mid-November to May (1927–29, 1939–42). There has been no evidence of spring mixing in recent years and bottom waters have become anoxic by late January. The diversity and density of offshore benthic organisms has declined from at least 12 species and an average density of 167000·m−2 in 1927 to 4–5 species at 15144 · m−2 in 1999. Overall, benthic populations shifted from the deepest portions of the lake (16–18 m benthos) to shallower depths and only Chaoborus was found at bottom contours > 10 m in 1999. Mean chloride concentration [Cl·] increased nearly 13-fold from 19 mg L−1 to 241 mg L−1 between 1981 and 1988, with 260 mg L−1 recorded in 1999. Calculations of whole-lake stability incorporating increases in [Cl·] indicate that about 60% more energy would be required to mix the lake following ice-out in 1999 compared to 1981. During the winter-spring transition, net respiration dominated under ice (4.1 g C·m−2 d−1) and immediately afterice-out(0.32 g C·m−2 d−1)in 1999. The phytoplankton community was dominated by cyanobacteria (Oscillatoria) from February to April. Under ice cover, bacterial abundance increased with depth from an average of 4.17 × 105 cells ml−1 (1–5 m) to 18.9 × 105 cells ml−1 (15 m).