The developmental history of Adirondack (N.Y.) lakes

We utilized paleoecological techniques to reconstruct long-term changes in lake-water chemistry, lake trophic state, and watershed vegetation and soils for three lakes located on an elevational gradient (661-1150 m) in the High Peaks region of the Adirondack Mountains of New York State (U.S.A.). Diatoms were used to reconstruct pH and trophic state. Sedimentary chrysophytes, chlorophylls and carotenoids supplied corroborating evidence. Pollen, plant macrofossils, and metals provided information on watershed vegetation, soils, and biogeochemical processes. All three lakes were slightly alkaline pH 7-8 and more productive in the late-glacial. They acidified and became less productive at the end of the late-glacial and in the early Holocene. pH stabilized 8000-9000 yr B.P. at the two higher sites and by 6000 yr B.P. at the lowest. An elevational gradient in pH existed throughout the Holocene. The highest site had a mean Holocene pH close to or below 5; the lowest site fluctuated around a mean of 6. The higher pH and trophic state of the late-glacial was controlled by leaching of base cations from fresh unweathered till, a process accelerated by the development of histosols in the watersheds as spruce-dominated woodlands replaced tundra. An apparent pulse of lake productivity at the late-glacial-Holocene boundary is correlated with a transient, but significant, expansion of alder (Alnus crispa) populations. The alder phase had a significant impact on watershed (and hence lake) biogeochemistry. The limnological changes of the Holocene and the differences between lakes were a function of an elevational gradient in temperature, hydrology (higher precipitation and lower evapotranspiration at higher elevation), soil thickness (thinner tills at higher elevation), soil type (histosols at higher elevation), vegetation (northern hardwoods at lower elevation, spruce-fir at higher), and different Holocene vegetational sequences in the three watersheds.