Controls on loss-on-ignition variation in cores from two shallow lakes in the northeastern United States

Loss-on-ignition analysis of Quaternary lake sediments provides an inexpensive and easy way to investigate past environmental changes. The mass loss on ignition at 550 degreesC (LOI) from lake sediment cores may vary because of temporal changes in: ( 1) sediment composition controlled by factors such as productivity, inorganic inputs, and decomposition; and ( 2) the patterns of sediment accumulation controlled by factors such as basin morphology and water level. Climatic changes can alter both. Here, modern surface samples and transects of sediment cores, collected across small (< 10 ha), shallow (< 4 m) lakes in the northeastern United States, show that LOI varies little ( 2 - 5%) across the deep portions of these small lakes at a given time. Large changes in LOI occur only at the transition into the littoral ( shallow) zone. LOI variations in sediment cores that exceed 2 - 5%, therefore, appear to represent meaningful environmental changes. However, because of the many possible controls, changes in the LOI of a single core are often hard to interpret. Multiple cores increase the interpretability. At lakes studied here, similar LOI trends among several cores confirm that some LOI changes resulted from basin-wide shifts in sediment composition. Differences among cores, however, developed during the early- and mid-Holocene and indicate that the edge of the littoral zone moved towards the centers of the lakes during two periods of low lake levels, at ca. 11 000 - 8000 and ca. 5400 - 3000 cal yr B. P. The basin-wide balance of sediment sources controlled the LOI from deep-water sediments, but sedimentation patterns, which changed as lake levels changed, were also important. LOI differences among cores may therefore help identify past lake-level changes in other lakes.